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Propeller II update - BLOG

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Comments

  • David BetzDavid Betz Posts: 14,511
    edited 2013-12-19 10:38
    pedward wrote: »
    Chip, why don't you just use an 8 bit byte for the LRU.

    When you load a cache line, shift the byte right, put the 2 bit line ID in the upper 2 bits. When you load the next line, you just pull the 2 bit ID off the bottom of the byte and use that to determine what the next cache line is.

    Init LRU to 11100100 at startup
    First load grabs 00, shifts right, pushes 00 to the top: 00111001
    Next load, so on.

    When the cogs start running instructions through the cache, the efficiency of the code will mix up the order, creating LRU instead of round-robin, but at start it will simply be round-robin.

    Also, I don't see how all tasks could want data at once, since they are staggered through the 4 stages of the pipeline. Sure, it takes 3-8 clocks to load, but the tasks will stall anyway. So, yes you can have a pile-up, and RDLONG should have priority over HUBEX, which will cause further stalls.

    This is all a better reason not to support HUBEX for more than task 0. You will have totally non-deterministic execution with 4 HUBEX tasks, because of issue order of the HUBEX loads and overriding priority for RDXXXX instructions. That means if the first instruction of a HUBEX is RDXXXX, it will stall the next HUBEX load, then if it's multiple RDXXXX instructions in a row, those other HUBEX tasks will stall indefinitely.

    If you only make 1 task HUBEX and have a 4 line cache, that will give best possible performance.

    pre-caching can make hub execution fast, but you must allow explicit memory ops to interrupt pending pre-cache requests.
    Don't you also need to keep a 13 bit tag for each line to remember what hub address it corresponds to and compare each instruction fetch address with all four of those simultaneously to determine if you have a hit on an already loaded line? And then if you do have a hit you need to delete the 2 bit tag for that line from the byte and add it to the front of the list to maintain the LRU ordering.
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 17:00
    Here is the latest instruction set reformatted...
    Postedit: Reduce screen magnification (Ctl + Scrollwheel) to view this table better! 
    ZCxS Opcode  ZC I Cond Dest      Source     Instr/00 01       10       11       Operand(s)                             Flags
--------------------------------------------------------------------------------------------------------------------------------
ZCWS 00000ff ZC I CCCC DDDDDDDDD SSSSSSSSS  RDBYTE   RDBYTEC  RDWORD   RDWORDC  D,S/PTRA/PTRB                          [WZ],[WC]
ZCWS 00001ff ZC I CCCC DDDDDDDDD SSSSSSSSS  RDLONG   RDLONGC  RDAUX    RDAUXR   D,S/PTRA/PTRB || D,S/#0..$FF/PTRX/PTRY [WZ],[WC]
ZCMS 00010ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ISOB     NOTB     CLRB     SETB     D,S/#                                  [WZ],[WC]
ZCMS 00011ff ZC I CCCC DDDDDDDDD SSSSSSSSS  SETBC    SETBNC   SETBZ    SETBNZ   D,S/#                                  [WZ],[WC]
ZCMS 00100ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ANDN     AND      OR       XOR      D,S/#                                  [WZ],[WC]
ZCMS 00101ff ZC I CCCC DDDDDDDDD SSSSSSSSS  MUXC     MUXNC    MUXZ     MUXNZ    D,S/#                                  [WZ],[WC]
ZCMS 00110ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ROR      ROL      SHR      SHL      D,S/#                                  [WZ],[WC]
ZCMS 00111ff ZC I CCCC DDDDDDDDD SSSSSSSSS  RCR      RCL      SAR      REV      D,S/#                                  [WZ],[WC]
ZCWS 01000ff ZC I CCCC DDDDDDDDD SSSSSSSSS  MOV      NOT      ABS      NEG      D,S/#                                  [WZ],[WC]
ZCWS 01001ff ZC I CCCC DDDDDDDDD SSSSSSSSS  NEGC     NEGNC    NEGZ     NEGNZ    D,S/#                                  [WZ],[WC]
ZCMS 01010ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ADD      SUB      ADDX     SUBX     D,S/#                                  [WZ],[WC]
ZCMS 01011ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ADDS     SUBS     ADDSX    SUBSX    D,S/#                                  [WZ],[WC]
ZCMS 01100ff ZC I CCCC DDDDDDDDD SSSSSSSSS  SUMC     SUMNC    SUMZ     SUMNZ    D,S/#                                  [WZ],[WC]
ZCMS 01101ff ZC I CCCC DDDDDDDDD SSSSSSSSS  MIN      MAX      MINS     MAXS     D,S/#                                  [WZ],[WC]
ZCMS 01110ff ZC I CCCC DDDDDDDDD SSSSSSSSS  ADDABS   SUBABS   INCMOD   DECMOD   D,S/#                                  [WZ],[WC]
ZCMS 01111ff ZC I CCCC DDDDDDDDD SSSSSSSSS  CMPSUB   SUBR     MUL      SCL      D,S/#                                  [WZ],[WC]
ZCWS 10000ff ZC I CCCC DDDDDDDDD SSSSSSSSS  DECOD2   DECOD3   DECOD4   DECOD5   D,S/#                                  [WZ],[WC]
Z-WS 100010f Zf I CCCC DDDDDDDDD SSSSSSSSS  ENCOD    BLMASK   ONECNT   ZERCNT   D,S/#                                  [WZ]
-CWS 1000110 fC I CCCC DDDDDDDDD SSSSSSSSS  INCPAT            DECPAT            D,S/#                                       [WC]
--WS 1000111 ff I CCCC DDDDDDDDD SSSSSSSSS  SPLITB   MERGEB   SPLITW   MERGEW   D,S/#                                  
--MS 10010nn nf I CCCC DDDDDDDDD SSSSSSSSS  GETNIB   SETNIB                     D,S/#,#0..7                            
--MS 1001100 nf I CCCC DDDDDDDDD SSSSSSSSS  GETWORD  SETWORD                    D,S/#,#0..1                            
--MS 1001101 ff I CCCC DDDDDDDDD SSSSSSSSS  STWORDS  ROLNIB   ROLBYTE  ROLWORD  D,S/#                                  
--MS 1001110 ff I CCCC DDDDDDDDD SSSSSSSSS  SETS     SETD     SETX     SETI     D,S/#                                  
-CMS 1001111 fC I CCCC DDDDDDDDD SSSSSSSSS  COGNEW            WAITCNT           D,S/#                                       [WC]
--MS 101000n nf I CCCC DDDDDDDDD SSSSSSSSS  GETBYTE  SETBYTE                    D,S/#,#0..3                            
--WS 1010010 ff I CCCC DDDDDDDDD SSSSSSSSS  STBYTES  SWBYTES  PACKRGB  UNPKRGB  D,S/#                                  
--MS 1010011 ff I CCCC DDDDDDDDD SSSSSSSSS  ADDPIX   MULPIX   BLNPIX   MIXPIX   D,S/#                                  
ZCMS 101010f ZC I CCCC DDDDDDDDD SSSSSSSSS  JMPSW    JMPSWD                     D,S/#                                  [WZ],[WC]
--MS 1010110 ff I CCCC DDDDDDDDD SSSSSSSSS  IJZ      IJZD     IJNZ     IJNZD    D,S/#                                  
--MS 1010111 ff I CCCC DDDDDDDDD SSSSSSSSS  DJZ      DJZD     DJNZ     DJNZD    D,S/#                                  
ZCRS 10110ff ZC I CCCC DDDDDDDDD SSSSSSSSS  TESTB    TESTN    TEST     CMP      D,S/#                                  [WZ],[WC]
ZCRS 10111ff ZC I CCCC DDDDDDDDD SSSSSSSSS  CMPX     CMPS     CMPSX    CMPR     D,S/#                                  [WZ],[WC]
--RS 11000nn nf I CCCC DDDDDDDDD SSSSSSSSS  COGINIT  WAITVID           WAITVID  D,S/#,#0..7 | #0..$DFF,S/# || D,S/#    
-CRS 11001fn nC I CCCC DDDDDDDDD SSSSSSSSS  WAITPEQ  WAITPNE                    D,S/#,#0..3                                 [WC]
--LS 110100f fL I CCCC DDDDDDDDD SSSSSSSSS  WRBYTE   WRWORD   WRLONG   FRAC     D/#,S/PTRA/PTRB ||| D/#,S/#            
--LS 110101f fL I CCCC DDDDDDDDD SSSSSSSSS  WRAUX    WRAUXR   SETACCA  SETACCB  D/#,S/#0..$FF/PTRX/PTRY || D/#,S/#     
--LS 110110f fL I CCCC DDDDDDDDD SSSSSSSSS  MACA     MACB     MUL32    MUL32U   D/#,S/#                                
--LS 110111f fL I CCCC DDDDDDDDD SSSSSSSSS  DIV32    DIV32U   DIV64    DIV64U   D/#,S/#                                
--LS 111000f fL I CCCC DDDDDDDDD SSSSSSSSS  SQRT64   QSINCOS  QARCTAN  QROTATE  D/#,S/#                                
--LS 111001f fL I CCCC DDDDDDDDD SSSSSSSSS  SETSERA  SETSERB  SETCTRS  SETWAVS  D/#,S/#                                
--LS 111010f fL I CCCC DDDDDDDDD SSSSSSSSS  SETFRQS  SETPHSS  ADDPHSS  SUBPHSS  D/#,S/#                                
--LS 111011f fL I CCCC DDDDDDDDD SSSSSSSSS  JP       JPD      JNP      JNPD     D/#,S/#                                
--LS 111100n nL I CCCC DDDDDDDDD SSSSSSSSS  CFGPINS                    JMPTASK  D/#,S/#,#0..2 | D/#,S/#                
--LS 111101f fL I CCCC DDDDDDDDD SSSSSSSSS  SETXFR   SETMIX   <empty>  <empty>  D/#,S/#                                
--RS 1111100 ff I CCCC DDDDDDDDD SSSSSSSSS  JZ       JZD      JNZ      JNZD     D,S/#                                  
--------------------------------------------------------------------------------------------------------------------------------
---- 1111101 ff n nnnn nnnnnnnnn nnnnnnnnn  AUGI                                #23bits                                
---- 1111101 01 0 nnnn nnnnnnnnn nnniiiiii  REPS                                #1..$10000,#1..64                      
---- 1111101 01 1 BBAA ddddddddd sssssssss  xxxINDx                             FIXINDx #d,#s | SETINDx #s | #d | #d,#
---- 1111101 10 0 CCCC ffnnnnnnn nnnnnnnnn  JMP      JMP_     JMP      JMP_     #abs | #abs | @rel | @rel              
---- 1111101 10 1 CCCC ffnnnnnnn nnnnnnnnn  JMPD     JMPD_    JMPD     JMPD_    #abs | #abs | @rel | @rel              
---- 1111101 11 0 CCCC ffnnnnnnn nnnnnnnnn  CALL     CALL_    CALL     CALL_    #abs | #abs | @rel | @rel              
---- 1111101 11 1 CCCC ffnnnnnnn nnnnnnnnn  CALLD    CALLD_   CALLD    CALLD_   #abs | #abs | @rel | @rel              
---- 1111110 00 0 CCCC ffnnnnnnn nnnnnnnnn  CALLA    CALLA_   CALLA    CALLA_   #abs | #abs | @rel | @rel              
---- 1111110 00 1 CCCC ffnnnnnnn nnnnnnnnn  CALLAD   CALLAD_  CALLAD   CALLAD_  #abs | #abs | @rel | @rel              
---- 1111110 01 0 CCCC ffnnnnnnn nnnnnnnnn  CALLB    CALLB_   CALLB    CALLB_   #abs | #abs | @rel | @rel              
---- 1111110 01 1 CCCC ffnnnnnnn nnnnnnnnn  CALLBD   CALLBD_  CALLBD   CALLBD_  #abs | #abs | @rel | @rel              
---- 1111110 10 0 CCCC ffnnnnnnn nnnnnnnnn  CALLX    CALLX_   CALLX    CALLX_   #abs | #abs | @rel | @rel              
---- 1111110 10 1 CCCC ffnnnnnnn nnnnnnnnn  CALLXD   CALLXD_  CALLXD   CALLXD_  #abs | #abs | @rel | @rel              
---- 1111110 11 0 CCCC ffnnnnnnn nnnnnnnnn  CALLY    CALLY_   CALLY    CALLY_   #abs | #abs | @rel | @rel              
---- 1111110 11 1 CCCC ffnnnnnnn nnnnnnnnn  CALLYD   CALLYD_  CALLYD   CALLYD_  #abs | #abs | @rel | @rel              
--------------------------------------------------------------------------------------------------------------------------------
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000000ff  COGID    LOCKNEW  GETPC    GETLFSR  D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000001ff  GETCNT   GETCNTX  GETACAL  GETACAH  D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000010ff  GETACBL  GETACBH  GETPTRA  GETPTRB  D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000011ff  GETPTRX  GETPTRY  SERINA   SERINB   D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000100ff  GETMULL  GETMULH  GETDIVQ  GETDIVR  D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000101ff  GETSQRT  GETQX    GETQY    GETQZ    D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000110ff  GETPHSA  GETPHZA  GETCOSA  GETSINA  D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 0000111ff  GETPHSB  GETPHZB  GETCOSB  GETSINB  D                                      [WZ],[WC]
ZCM- 1111111 ZC 0 CCCC DDDDDDDDD 0001000ff  PUSHZC   POPZC    SUBCNT   GETPIX   D                                      [WZ],[WC]
ZCM- 1111111 ZC 0 CCCC DDDDDDDDD 0001001ff  BINBCD   BCDBIN   BINGRY   GRYBIN   D                                      [WZ],[WC]
ZCM- 1111111 ZC 0 CCCC DDDDDDDDD 0001010ff  ESWAP4   ESWAP8   SEUSSF   SEUSSR   D                                      [WZ],[WC]
Z-M- 1111111 ZC 0 CCCC DDDDDDDDD 0001011ff  INCD     DECD     INCDS    DECDS    D                                      [WZ],[WC]
ZCW- 1111111 ZC 0 CCCC DDDDDDDDD 000110000  POP                                 D                                      [WZ],[WC]
--L- 1111111 00 L CCCC DDDDDDDDD 001iiiiii  REPD                                D/#1..512,#1..64                       
--L- 1111111 00 L CCCC DDDDDDDDD 0100000ff  CLKSET   COGSTOP  LOCKSET  LOCKCLR  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0100001ff  LOCKRET  RDWIDEC  RDWIDE   WRWIDE   D/# | D/PTRA/PTRB                      
ZCL- 1111111 ZC L CCCC DDDDDDDDD 0100010ff  GETP     GETNP    SEROUTA  SEROUTB  D/#                                    [WZ],[WC]
-CL- 1111111 0C L CCCC DDDDDDDDD 0100011ff  CMPCNT   WAITPX   WAITPR   WAITPF   D/#                                         [WC]
ZCL- 1111111 ZC L CCCC DDDDDDDDD 0100100ff  SETZC    SETMAP   SETXCH   SETTASK  D/#                                    [WZ],[WC]
--L- 1111111 00 L CCCC DDDDDDDDD 0100101ff  SETRACE  SARACCA  SARACCB  SARACCS  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0100110ff  SETPTRA  SETPTRB  ADDPTRA  ADDPTRB  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0100111ff  SUBPTRA  SUBPTRB  SETWIDE  SETWIDZ  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101000ff  SETPTRX  SETPTRY  ADDPTRX  ADDPTRY  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101001ff  SUBPTRX  SUBPTRY  PASSCNT  WAIT     D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101010ff  OFFP     NOTP     CLRP     SETP     D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101011ff  SETPC    SETPNC   SETPZ    SETPNZ   D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101100ff  DIV64D   SQRT32   QLOG     QEXP     D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101101ff  SETQI    SETQZ    CFGDACS  SETDACS  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101110ff  CFGDAC0  CFGDAC1  CFGDAC2  CFGDAC3  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0101111ff  SETDAC0  SETDAC1  SETDAC2  SETDAC3  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110000ff  SETCTRA  SETWAVA  SETFRQA  SETPHSA  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110001ff  ADDPHSA  SUBPHSA  SETVID   SETVIDY  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110010ff  SETCTRB  SETWAVB  SETFRQB  SETPHSB  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110011ff  ADDPHSB  SUBPHSB  SETVIDI  SETVIDQ  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110100ff  SETPIX   SETPIXZ  SETPIXU  SETPIXV  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110101ff  SETPIXA  SETPIXR  SETPIXG  SETPIXB  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110110ff  SETPORA  SETPORB  SETPORC  SETPORD  D/#                                    
--L- 1111111 00 L CCCC DDDDDDDDD 0110111ff  PUSH     <empty>  JMPREL   JMPRELD  D/# | D/# | D | D                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111010ff  JMP      JMP_     JMPD     JMPD_    D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111011ff  CALL     CALL_    CALLD    CALLD_   D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111100ff  CALLA    CALLA_   CALLAD   CALLAD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111101ff  CALLB    CALLB_   CALLBD   CALLBD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111110ff  CALLX    CALLX_   CALLXD   CALLXD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111111ff  CALLY    CALLY_   CALLYD   CALLYD_  D                                      
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000000ff  RETA     RETAD    RETB     RETBD                                           [WZ],[WC]
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000001ff  RETX     RETXD    RETY     RETYD                                           [WZ],[WC]
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000010ff  RET      RETD     POLCTRA  POLCTRB                                         [WZ],[WC]
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000011ff  POLVID   CAPCTRA  CAPCTRB  CAPCTRS                                         [WZ],[WC]
---- 1111111 00 x CCCC xxxxxxxxx 1000100ff  CACHEX   CLRACCA  CLRACCB  CLRACCS                                         
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000101ff  CHKPTRX  CHKPTRY  SYNCTRA  SYNCTRB                                         [WZ],[WC]
---- 1111111 00 x CCCC xxxxxxxxx 1000110ff  SETPIXW  <empty>  <empty>  <empty>                                         
--------------------------------------------------------------------------------------------------------------------------------
    InstructionSet_20131217a.spin
    spin
    spin
    InstructionSet_20131217a.spin
    14K
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 17:07
    QUESTION FOR EVERYONE

    Would it be too disruptive to get rid of the #address requirement for constant branches and then use @register to denote register?

    These:

    JMP #label
    JMP register

    Would become:

    JMP label
    JMP @register


    What do you think?

    It would get rid of a lot of #'s in source code and introduce an occasional @. This is more like what newcomers would expect, but it differs from Prop1.
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 17:40
    Then how would relative branches be specified?
    @n for absolute
    @+n for jump relative positive offset
    @-n for jump relative negative offset

    would work.

    Or do you mean get rid of absolute jmp's?
    cgracey wrote: »
    QUESTION FOR EVERYONE

    Would it be too disruptive to get rid of the #address requirement for constant branches and then use @register to denote register?

    These:

    JMP #label
    JMP register

    Would become:

    JMP label
    JMP @register


    What do you think?

    It would get rid of a lot of #'s in source code and introduce an occasional @. This is more like what newcomers would expect, but it differs from Prop1.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 17:43
    Bill Henning wrote: »
    Then how would relative branches be specified?
    @n for absolute
    @+n for jump relative positive offset
    @-n for jump relative negative offset

    would work.

    Or do you mean get rid of absolute jmp's?


    It's actually looking to me like absolute jumps are kind of worthless. You don't need them in the cog. And in the hub, is it realistic to know the absolute address of something that's not you? I think a register would better hold a value for such a purpose What do you think?
  • pedwardpedward Posts: 1,642
    edited 2013-12-19 17:48
    The # syntax was always and odd in my opinion.
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 18:05
    I am OK without absolute jumps; it will just take a bit more thinking for jump tables like VM opcode dispatch tables.
    cgracey wrote: »
    It's actually looking to me like absolute jumps are kind of worthless. You don't need them in the cog. And in the hub, is it realistic to know the absolute address of something that's not you? I think a register would better hold a value for such a purpose What do you think?
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 18:10
    Uh-Oh.

    Without absolute jumps, how will hubexec code call cog subroutines or jump to them?
    cgracey wrote: »
    It's actually looking to me like absolute jumps are kind of worthless. You don't need them in the cog. And in the hub, is it realistic to know the absolute address of something that's not you? I think a register would better hold a value for such a purpose What do you think?
  • bruceebrucee Posts: 239
    edited 2013-12-19 18:14
    Most other CPUs out there use relative addressing, works great for short or intermediate length jumps/calls.

    In a 32bit address space with a 32 bit instruction, you don't have many options, unless you want to give up 1/2 of the instruction set range to handle absolute jumps.

    In the case where you need an absolute jump, the mechanism is to generate a 32 bit constant, load it into a register, then branch to the register.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 18:15
    Bill Henning wrote: »
    Uh-Oh.

    Without absolute jumps, how will hubexec code call cog subroutines or jump to them?


    You're right. Wait...

    Any branch that ends in underscore is cog/hub-mode toggling. Those jumps cannot be relative, because there's no sensible relationship between cog and hub execution address. I could just have those encoded as absolutes in the assembler and have the cog hardware handle them as absolutes. That would let us consolidate with one constant address syntax, so we could get rid of #. What do you think?
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 18:16
    cgracey wrote: »
    QUESTION FOR EVERYONE

    Would it be too disruptive to get rid of the #address requirement for constant branches and then use @register to denote register?

    These:

    JMP #label
    JMP register

    Would become:

    JMP label
    JMP @register


    What do you think?

    It would get rid of a lot of #'s in source code and introduce an occasional @. This is more like what newcomers would expect, but it differs from Prop1.
    I would much prefer the @ case because it basically means indirect.

    However, compatibility is to some extent a problem. Maybe later the compilers could have a compatibility bit to switch back to the P1 style modes.

    As for relative vs absolute, this is more of a compiler issue isn't it?

    eg
    JMP label
    would be created as a relative or absolute immediate instruction by the compiler.

    But,
    JMP @register
    would the contents of the register be absolute or relative???
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 18:22
    For reference, here are all the JMP/CALL/RET instructions 
    ZCxS Opcode  ZC I Cond Dest      Source     Instr/00 01       10       11       Operand(s)                             Flags
--------------------------------------------------------------------------------------------------------------------------------
ZCMS 101010f ZC I CCCC DDDDDDDDD SSSSSSSSS  JMPSW    JMPSWD                     D,S/#                                  [WZ],[WC]
--MS 1010110 ff I CCCC DDDDDDDDD SSSSSSSSS  IJZ      IJZD     IJNZ     IJNZD    D,S/#                                  
--MS 1010111 ff I CCCC DDDDDDDDD SSSSSSSSS  DJZ      DJZD     DJNZ     DJNZD    D,S/#                                  
--LS 111011f fL I CCCC DDDDDDDDD SSSSSSSSS  JP       JPD      JNP      JNPD     D/#,S/#                                
--LS 111100n nL I CCCC DDDDDDDDD SSSSSSSSS  CFGPINS                    JMPTASK  D/#,S/#,#0..2 | D/#,S/#                
--RS 1111100 ff I CCCC DDDDDDDDD SSSSSSSSS  JZ       JZD      JNZ      JNZD     D,S/#                                  
--------------------------------------------------------------------------------------------------------------------------------
---- 1111101 ff n nnnn nnnnnnnnn nnnnnnnnn  AUGI                                #23bits                                
---- 1111101 10 0 CCCC ffnnnnnnn nnnnnnnnn  JMP      JMP_     JMP      JMP_     #abs | #abs | @rel | @rel              
---- 1111101 10 1 CCCC ffnnnnnnn nnnnnnnnn  JMPD     JMPD_    JMPD     JMPD_    #abs | #abs | @rel | @rel              
---- 1111101 11 0 CCCC ffnnnnnnn nnnnnnnnn  CALL     CALL_    CALL     CALL_    #abs | #abs | @rel | @rel              
---- 1111101 11 1 CCCC ffnnnnnnn nnnnnnnnn  CALLD    CALLD_   CALLD    CALLD_   #abs | #abs | @rel | @rel              
---- 1111110 00 0 CCCC ffnnnnnnn nnnnnnnnn  CALLA    CALLA_   CALLA    CALLA_   #abs | #abs | @rel | @rel              
---- 1111110 00 1 CCCC ffnnnnnnn nnnnnnnnn  CALLAD   CALLAD_  CALLAD   CALLAD_  #abs | #abs | @rel | @rel              
---- 1111110 01 0 CCCC ffnnnnnnn nnnnnnnnn  CALLB    CALLB_   CALLB    CALLB_   #abs | #abs | @rel | @rel              
---- 1111110 01 1 CCCC ffnnnnnnn nnnnnnnnn  CALLBD   CALLBD_  CALLBD   CALLBD_  #abs | #abs | @rel | @rel              
---- 1111110 10 0 CCCC ffnnnnnnn nnnnnnnnn  CALLX    CALLX_   CALLX    CALLX_   #abs | #abs | @rel | @rel              
---- 1111110 10 1 CCCC ffnnnnnnn nnnnnnnnn  CALLXD   CALLXD_  CALLXD   CALLXD_  #abs | #abs | @rel | @rel              
---- 1111110 11 0 CCCC ffnnnnnnn nnnnnnnnn  CALLY    CALLY_   CALLY    CALLY_   #abs | #abs | @rel | @rel              
---- 1111110 11 1 CCCC ffnnnnnnn nnnnnnnnn  CALLYD   CALLYD_  CALLYD   CALLYD_  #abs | #abs | @rel | @rel              
--------------------------------------------------------------------------------------------------------------------------------
--L- 1111111 00 L CCCC DDDDDDDDD 0110111ff  PUSH     <empty>  JMPREL   JMPRELD  D/# | D/# | D | D                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111010ff  JMP      JMP_     JMPD     JMPD_    D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111011ff  CALL     CALL_    CALLD    CALLD_   D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111100ff  CALLA    CALLA_   CALLAD   CALLAD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111101ff  CALLB    CALLB_   CALLBD   CALLBD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111110ff  CALLX    CALLX_   CALLXD   CALLXD_  D                                      
--R- 1111111 00 0 CCCC DDDDDDDDD 0111111ff  CALLY    CALLY_   CALLYD   CALLYD_  D                                      
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000000ff  RETA     RETAD    RETB     RETBD                                           [WZ],[WC]
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000001ff  RETX     RETXD    RETY     RETYD                                           [WZ],[WC]
ZC-- 1111111 ZC x CCCC xxxxxxxxx 1000010ff  RET      RETD     POLCTRA  POLCTRB                                         [WZ],[WC]
--------------------------------------------------------------------------------------------------------------------------------
  • ElectrodudeElectrodude Posts: 1,621
    edited 2013-12-19 18:28
    cgracey wrote: »
    QUESTION FOR EVERYONE

    Would it be too disruptive to get rid of the #address requirement for constant branches and then use @register to denote register?

    These:

    JMP #label
    JMP register

    Would become:

    JMP label
    JMP @register


    What do you think?

    It would get rid of a lot of #'s in source code and introduce an occasional @. This is more like what newcomers would expect, but it differs from Prop1.

    If this was only for branches, it would be unnecessarily inconsistent. If it was for everything, add @a, @b would be a headache. I like the Prop 1 method way better, even though I forget #'s all the time. How about keep it the Prop 1 way but make a compiler warning if you say jmp label, where label is initially a command and not a res or long? Maybe whether or not the compiler should emit this warning could be user configurable.

    electrodude
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 18:37
    I've been chewing on this.

    I agree that jumps between modes have to be absolute, as relative addresses do not make sense there. So you can save some instruction encodings there.

    I have niggling feeling that we would regred not having both absolute and relative within the same mode.

    I think what would work best:

    cog-cog absolute and relative addressing
    hub-hub absolute and relative addressing
    cog-hub absolute addressing only
    hub-cog absolute addressing only
    cgracey wrote: »
    You're right. Wait...

    Any branch that ends in underscore is cog/hub-mode toggling. Those jumps cannot be relative, because there's no sensible relationship between cog and hub execution address. I could just have those encoded as absolutes in the assembler and have the cog hardware handle them as absolutes. That would let us consolidate with one constant address syntax, so we could get rid of #. What do you think?
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 18:48
    There are certainly a lot of JMP/CALL instructions.

    I am not sure why toggling is required though???

    IMHO there are 2 basic cases

    JMP/CALL to Hub
    JMP/CALL to Cog

    These two cover the cases of:
    Hub JMP/CALL to Hub
    Hub JMP/CALL to Cog
    Cog JMP/CALL to Hub
    Cog JMP/CALL to Cog

    The compiler will know whether it is in hub or cog mode, and whether the call will be to hub or cog.
    So I cannot see why we need a toggle JMP/CALL.
    Am I missing something here???

    Next, there are D (delayed versions).
    And lastly, we need to see which hub and cog modes require..
    Immediate Absolute
    Immediate Relative
    Indirect Absolute (register)
    Indirect Relative (register)

    To me, it makes sense for the Indirect JMP/CALL to use "@register".

    Many, including myself, often forget the "#" for the immediate absolute. I would rather ditch it or have an option to include/warn in the compiler - I usually check my code with bst as it gives a warning - there are only 4 cases in the whole ZiCog code that actually use a register.
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 18:58
    Bill Henning wrote: »
    I've been chewing on this.

    I agree that jumps between modes have to be absolute, as relative addresses do not make sense there. So you can save some instruction encodings there.

    I have niggling feeling that we would regred not having both absolute and relative within the same mode.

    I think what would work best:

    cog-cog absolute and relative addressing
    hub-hub absolute and relative addressing
    cog-hub absolute addressing only
    hub-cog absolute addressing only

    Agreed, I cannot see the use of relative addressing for cog-hub or hub-cog mode switching. If anything is relative, then the sw would have to add the base to it, because there is not reference for the hw at runtime. Relative is only consistent within cog-cog and hub-hub.

    On the P1 we don't have relative for cog-cog, but it would be nice. At some time, it may make expanding cog beyond 512 longs possible (with some simple caveats). I would love to access AUX as extended Cog ram.

    Relative makes a lot more sense with hub mode although Chip has found 16bits of (immediate) address for absolute/relative.
    Relative facilitates relocatable code, beyond the base.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 19:02
    Cluso99 wrote: »
    I would much prefer the @ case because it basically means indirect.

    However, compatibility is to some extent a problem. Maybe later the compilers could have a compatibility bit to switch back to the P1 style modes.

    As for relative vs absolute, this is more of a compiler issue isn't it?

    eg
    JMP label
    would be created as a relative or absolute immediate instruction by the compiler.

    But,
    JMP @register
    would the contents of the register be absolute or relative???


    'JMP/CALL @register' would be absolute.
    'JMP_/CALL_ @register' would be absolute.

    'JMP/CALL label' would be relative
    'JMP_/CALL_ label' would be absolute

    So, all would be absolute except non-toggling constant branches. They would be relative.
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 19:16
    Bill,
    Thinking further...

    In hub mode...

    Relative addressing can be computed by the compiler. This makes the code relocatable. These relative addresses would be held within the JMP/CALL instructions (17 typo 16 bits). I cannot see a need to have Relative addressing held in registers - can you???

    But the original call to the module would need to be done by an Absolute JMP/CALL.
    Most likely, the Absolute address would need to be held in a register because you don't want to plug absolute addresses into instructions within hub.
    However, we will also require the JMP/CALL from hub to cog to contain the absolute cog address within the instruction, and also cog to hub.
    So it makes sense for JMP/CALLs to Hub or Cog to have absolute addresses contained within the instruction, as well as in a register.

    Does this make sense???
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 19:16
    Sorry Chip, I am getting a bit confused.
    cgracey wrote: »
    'JMP/CALL @register' would be absolute.
    'JMP_/CALL_ @register' would be absolute.

    'JMP/CALL label' would be relative
    'JMP_/CALL_ label' would be absolute

    So, all would be absolute except non-toggling constant branches. They would be relative.

    cog-cog absolute and relative addressing - I think we need both. Relative for relocatable snippets, and absolute for calling subroutine libraries, or jumping to known fixed entry points
    hub-hub absolute and relative addressing - I think we need both. Relative for relocatable snippets, and absolute for calling subroutine libraries, or jumping to known fixed entry points

    cog-hub absolute addressing only, as relative does not make sense.
    hub-cog absolute addressing only, as relative does not make sense

    I like using @absoluteaddr convention for labels, and @$1234 works for fixed absolute numbers.
    I am concerned with using 'jmp label' to indicate relative jumps, as that would normally indicate jump to content of register.

    Perhaps

    jmp/call @addr indicates a relative jmp/call to the label addr (valid for cog-cog, hub-hub)
    jmp/call #addr indicates an absolute jmp/call (consistent with P1) (valid for cog-cog, hub-hub, cog-hub, hub-cog)
    jmp/call reg indicates an indirect jmp/call to the contents of reg (valid for cog-cog, hub-hub, cog-hub, hub-cog)

    The more I think of it, the more certain I become that we should keep absolute calls/jumps for all modes.
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 19:18
    Cluso99 wrote: »
    Bill,
    Thinking further...

    In hub mode...

    Relative addressing can be computed by the compiler. This makes the code relocatable. These relative addresses would be held within the JMP/CALL instructions (17 bits). I cannot see a need to have Relative addressing held in registers - can you???

    Agreed, no need to have relative-indirect. Only 16 bits needed, as all hub instructions must be long aligned.

    This would also allow storing CAR/CDR in one long for CONS :) and manipulating them easily with GETWORD and SETWORD :):)
    Cluso99 wrote: »
    But the original call to the module would need to be done by an Absolute JMP/CALL.
    Most likely, the Absolute address would need to be held in a register because you don't want to plug absolute addresses into instructions within hub.
    However, we will also require the JMP/CALL from hub to cog to contain the absolute cog address within the instruction, and also cog to hub.
    So it makes sense for JMP/CALLs to Hub or Cog to have absolute addresses contained within the instruction, as well as in a register.

    Does this make sense???

    See my previous post (right before this one) I think I have all the usage cases, please let me know if I missed something... or if something should be added.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 19:19
    By having toggling jumps and calls, you cut the number of instructions in half.

    While in hub mode, you'll want to call to both hub and cog code. When in cog mode, you'll want to call both hub and cog code.

    Cluso99 wrote: »
    There are certainly a lot of JMP/CALL instructions.

    I am not sure why toggling is required though???

    IMHO there are 2 basic cases

    JMP/CALL to Hub
    JMP/CALL to Cog

    These two cover the cases of:
    Hub JMP/CALL to Hub
    Hub JMP/CALL to Cog
    Cog JMP/CALL to Hub
    Cog JMP/CALL to Cog

    The compiler will know whether it is in hub or cog mode, and whether the call will be to hub or cog.
    So I cannot see why we need a toggle JMP/CALL.
    Am I missing something here???

    Next, there are D (delayed versions).
    And lastly, we need to see which hub and cog modes require..
    Immediate Absolute
    Immediate Relative
    Indirect Absolute (register)
    Indirect Relative (register)

    To me, it makes sense for the Indirect JMP/CALL to use "@register".

    Many, including myself, often forget the "#" for the immediate absolute. I would rather ditch it or have an option to include/warn in the compiler - I usually check my code with bst as it gives a warning - there are only 4 cases in the whole ZiCog code that actually use a register.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 19:24
    Bill Henning wrote: »
    jmp/call @addr indicates a relative jmp/call to the label addr (valid for cog-cog, hub-hub)
    jmp/call #addr indicates an absolute jmp/call (consistent with P1) (valid for cog-cog, hub-hub, cog-hub, hub-cog)
    jmp/call reg indicates an indirect jmp/call to the contents of reg (valid for cog-cog, hub-hub, cog-hub, hub-cog)


    This is exactly how it's set up at the moment.

    I was thinking if we could come up with some set rules for constants in different circumstances, we could adopt very simple syntax.
  • David BetzDavid Betz Posts: 14,511
    edited 2013-12-19 19:26
    cgracey wrote: »
    By having toggling jumps and calls, you cut the number of instructions in half.

    While in hub mode, you'll want to call to both hub and cog code. When in cog mode, you'll want to call both hub and cog code.
    I still don't see why you couldn't have a separate hub and cog version of each jmp and call. It would be the same number of instructions as having a non-mode-changing instruction and a mode-changing-instruction.

    Instead of:

    JMP
    JMP_

    You have:

    JMP
    HJMP

    Where JMP means "jump to a COG address" and HJMP means "jump to a hub address". Seems more intuitive to me.
  • Bill HenningBill Henning Posts: 6,445
    edited 2013-12-19 19:32
    Honestly?

    I think that what we have is the simplest.

    I feel as soon as any of the current capability (except for inter-modal call/jmp) is removed, we would get bitten by the lack.

    Having subroutines at fixed location is very useful for libraries, system calls etc.

    Indirect jumps/calls are very useful for function pointers and jump tables.

    Relative jumps/calls are very useful for relocatable code.

    I think we are asking for trouble if we try to eliminate any of these (except when switching modes, relative inter-modal adresses do not make any sense)
    cgracey wrote: »
    This is exactly how it's set up at the moment.

    I was thinking if we could come up with some set rules for constants in different circumstances, we could adopt very simple syntax.
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 19:35
    cgracey wrote: »
    'JMP/CALL @register' would be absolute.
    'JMP_/CALL_ @register' would be absolute.

    'JMP/CALL label' would be relative
    'JMP_/CALL_ label' would be absolute

    So, all would be absolute except non-toggling constant branches. They would be relative.

    Chip,

    I cannot see the requirement for the toggling mode, although the hardware needs to know where the instruction pc is going. But in sw, the user doesn't want to know about this.
    dat
        COGMODE
        org   0
doloop  ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubloop   ' call hub routine
        ...
subr    ...
        RETX            ' return to caller (cog or hub)
        HUBMODE
        orgh  $4000
hubloop ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubsub    ' call hub routine
        ...
        RETY            ' return to caller (cog or hub)
hubsub  ...
        RETY            ' return to caller (cog or hub)

    In the above cases, the compiler would use the correct JMP/CALL instruction. But I don't see a toggle case, but rather the specific case of the compiler inserting either a hub or cog CALL.

    It doesn't actually save anything, but from a user perspective it sounds simpler (to me anyway). So the CALL & CALL_ become a COG CALL and a HUB CALL instead of a same cog/hub CALL and a toggle cog/hub CALL. This way, the specific CALL (say CALL (for cog) & CALLH) reset/set the hubexec mode bit in the ALU.

    Does this make sense???
  • David BetzDavid Betz Posts: 14,511
    edited 2013-12-19 19:39
    Cluso99 wrote: »
    Chip,

    I cannot see the requirement for the toggling mode, although the hardware needs to know where the instruction pc is going. But in sw, the user doesn't want to know about this.
    dat
        COGMODE
        org   0
doloop  ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubloop   ' call hub routine
        ...
subr    ...
        RETX            ' return to caller (cog or hub)
        HUBMODE
        orgh  $4000
hubloop ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubsub    ' call hub routine
        ...
        RETY            ' return to caller (cog or hub)
hubsub  ...
        RETY            ' return to caller (cog or hub)

    In the above cases, the compiler would use the correct JMP/CALL instruction. But I don't see a toggle case, but rather the specific case of the compiler inserting either a hub or cog CALL.

    It doesn't actually save anything, but from a user perspective it sounds simpler (to me anyway). So the CALL & CALL_ become a COG CALL and a HUB CALL instead of a same cog/hub CALL and a toggle cog/hub CALL. This way, the specific CALL (say CALL (for cog) & CALLH) reset/set the hubexec mode bit in the ALU.

    Does this make sense???
    I tried to suggest this a while back. I think you're saying to use that extra bit to select hub or COG addresses in the CALL and JMP instructions. The other option is what I mentioned in the post just before yours, that we just use two different opcodes. Both result in the same binary being generated where the bit that Chip is currently using to distinguish the XXX and XXX_ instructions gets used to select hub vs. COG. That seems a lot simpler to me than the toggle although there might be some hardware reason that Chip prefers the toggle.
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 19:51
    Bill Henning wrote: »
    Sorry Chip, I am getting a bit confused.



    cog-cog absolute and relative addressing - I think we need both. Relative for relocatable snippets, and absolute for calling subroutine libraries, or jumping to known fixed entry points
    hub-hub absolute and relative addressing - I think we need both. Relative for relocatable snippets, and absolute for calling subroutine libraries, or jumping to known fixed entry points

    cog-hub absolute addressing only, as relative does not make sense.
    hub-cog absolute addressing only, as relative does not make sense


    There are more cases to these... where the addresses are stored in registers or as an immediate value (in the 16 bits - was a typo before)
    I will put the cases in a table shortly.
             COG-COG      COG-HUB      HUB-COG     HUB-HUB
ABS     #IMM @REG   #IMM  @REG   #IMM  @REG   #IMM @REG
REL     #IMM @REG   ????  ????   ????  ????   #IMM @REG

ABS     call CALL   call_ CALL_  call_ CALL_  call CALL
REL     call  na    call_  na    call_  na    call  na
    I like using @absoluteaddr convention for labels, and @$1234 works for fixed absolute numbers.
    I am concerned with using 'jmp label' to indicate relative jumps, as that would normally indicate jump to content of register.

    Perhaps

    jmp/call @addr indicates a relative jmp/call to the label addr (valid for cog-cog, hub-hub)
    jmp/call #addr indicates an absolute jmp/call (consistent with P1) (valid for cog-cog, hub-hub, cog-hub, hub-cog)
    jmp/call reg indicates an indirect jmp/call to the contents of reg (valid for cog-cog, hub-hub, cog-hub, hub-cog)
    I strongly disagree here...

    @ should be used for indirection (ie the address is stored in a register - complication is, is it relative or absolute?)
    # could be optional (for P1 compatibility) but would indicate the address is stored within the instruction (ie immediate - same complication, is it relative or absolute?)

    Some other micros use BRA for relative jumps but this does not solve the CALL problem.

    The more I think of it, the more certain I become that we should keep absolute calls/jumps for all modes.
  • YanomaniYanomani Posts: 1,524
    edited 2013-12-19 19:59
    David Betz wrote: »
    I tried to suggest this a while back. I think you're saying to use that extra bit to select hub or COG addresses in the CALL and JMP instructions. The other option is what I mentioned in the post just before yours, that we just use two different opcodes. Both result in the same binary being generated where the bit that Chip is currently using to distinguish the XXX and XXX_ instructions gets used to select hub vs. COG. That seems a lot simpler to me than the toggle although there might be some hardware reason that Chip prefers the toggle.

    David

    IMHO, you're right. Chip's thoughts seems to be driven by implicit hardware reasons.
    Perhaps it's due to the fact, that a toggle bit is already there, selecting from where pipeline's first stage is to be loaded, Cog or Hub.
    It must also exists, to enable the LRU caching mechanism.

    So, it's an almost free differentiator bit, that must be there anyway.

    Yanomani
  • Cluso99Cluso99 Posts: 18,069
    edited 2013-12-19 20:13
    David Betz wrote: »
    I tried to suggest this a while back. I think you're saying to use that extra bit to select hub or COG addresses in the CALL and JMP instructions. The other option is what I mentioned in the post just before yours, that we just use two different opcodes. Both result in the same binary being generated where the bit that Chip is currently using to distinguish the XXX and XXX_ instructions gets used to select hub vs. COG. That seems a lot simpler to me than the toggle although there might be some hardware reason that Chip prefers the toggle.
    This is exactly my thoughts too. Currently I cannot see any advantage to toggling and it just seems safer to explicitly select the correct mode rather than toggling.
    It is just that the compiler will see it differently.

    BTW I updated my earlier post with a table of instructions for all the modes.
  • cgraceycgracey Posts: 14,133
    edited 2013-12-19 20:13
    Cluso99 wrote: »
    Chip,

    I cannot see the requirement for the toggling mode, although the hardware needs to know where the instruction pc is going. But in sw, the user doesn't want to know about this.
    dat
        COGMODE
        org   0
doloop  ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubloop   ' call hub routine
        ...
subr    ...
        RETX            ' return to caller (cog or hub)
        HUBMODE
        orgh  $4000
hubloop ...
        ...
        CALLX subr      ' call cog routine
        ...
        CALLY hubsub    ' call hub routine
        ...
        RETY            ' return to caller (cog or hub)
hubsub  ...
        RETY            ' return to caller (cog or hub)

    In the above cases, the compiler would use the correct JMP/CALL instruction. But I don't see a toggle case, but rather the specific case of the compiler inserting either a hub or cog CALL.

    It doesn't actually save anything, but from a user perspective it sounds simpler (to me anyway). So the CALL & CALL_ become a COG CA7gLL and a HUB CALL instead of a same cog/hub CALL and a toggle cog/hub CALL. This way, the specific CALL (say CALL (for cog) & CALLH) reset/set the hubexec mode bit in the ALU.

    Does this make sense???


    You're right that for constant jumps and calls the assembler can know if it's going to hub from cog, to cog from hub, or staying in the cog or hub. This could get rid of the "_" versions of branches.

    We could have either toggling and non-toggling branches, or fixed cog and fixed hub branches. The latter seems simpler, but will inhibit code from working in both cog and hub. There's also the issue of the 9-bit constant branches (DJNZ, etc.) needing to work in both cog and hub. For these reasons, I think a toggling system is better, regardless of the syntax.
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