CALLB #\A Syntax Question

Bob Drury · 2021-10-04 16:37

Curious about setting register PTRB? CogInit has PTRA as a pointer that can be set when calling PASM program. What about PTRB? Is this just set within a PASM program? The atached code seems to work by
setting PTRB in the program, but if I remove MOV PTRB,##PTRB_Stack statement it stills works. I think
the reason it still works is PTRB = 0 and the stack is pointing to Hub Ram =0 which would mean
the Spin2 code is overwritten and since there is no spin2 code it doesn't matter.
Comments on how to best set PTRB would be apreciated.
Regards
Bob (WRD)

CON {Processor Timing}
  _clkfreq  = 200_000_000  'processor clock speed
VAR
    Byte cogStarted_COGEXEC_NEW 'cog ID started is returned or -1 if not started

OBJ
PUB main()
     cogStarted_COGEXEC_NEW := COGINIT(COGEXEC_NEW,@CallProgram,$FFFF_FFFF)
     repeat  'keep cog 0 running
DAT          ORGH          'Assign stack in Hub Ram
PTRB_Stack   long    8
DAT          ORG     0     'COGINIT(COGEXEC_NEW,@CallProgram,$FFFF_FFFF)
CallProgram  NOP
             MOV PTRB,##PTRB_Stack
             CALLB #Subroutine 'Compiler takes Subroutine-Call Program and generates offset
             debug("Returned from Subroutine")
             debug(udec(POPBNum01),udec(POPBNum02),udec(POPBNum03))
             debug(udec(POPBNum04),udec(POPBNum05),udec(POPBNum06),udec(POPBNum07))
Loop1        NOP
             JMP  #LooP1
Subroutine   NOP
             debug("Now In Subroutine")
             WAITX clkTicks
             debug("PUSHB Num01 to Num07")
             PUSHB Num01
             PUSHB Num02
             PUSHB Num03
             PUSHB Num04
             PUSHB Num05
             PUSHB Num06
             PUSHB Num07
             WAITX clkTicks
             debug("POPB POPBNum07 to POPBNum01")
             POPB   POPBNum07
             POPB   POPbNum06
             POPB   POPBNum05
             POPB   POPBNum04
             POPB   POPBNum03
             POPB   POPBNum02
             POPB   POPBNum01
             RETB
Loop2        NOP
             JMP #Loop2

clkTicks     long     $00A00_0000
Num01        long     1
Num02        long     2
Num03        long     3
Num04        long     4
Num05        long     5
Num06        long     6
Num07        long     7
POPBNum01     long     0
POPBNum02     long     0
POPBNum03     long     0
POPBNum04     long     0
POPBNum05     long     0
POPBNum06     long     0
POPBNum07     long     0

AJL · 2021-10-05 00:08

Bob,

PTRB** can** be used like any other cogram long, but given that it is loaded with the program address on COGINIT, and all of the pointer related machinery associated with it, it makes most sense to use it as a hubram pointer.

I wouldn't be surprised to find that cog0 is affected. If you were to setup a pair of instructions to toggle a pin (for a pin with an LED attached) and wait (e.g. 100ms), in the SPIN2 repeat clause, you might see whether the SPIN2 code in cog0 is corrupted.
Edit: With an empty repeat loop the SPIN2 interpreter may not fetch anything from hubram. I wouldn't expect you to be able to restart cog0 and get the same results after running this code.

Also note, that unlike the Propeller 1, you don't actually need a SPIN2 stub to start off a PASM2 program. As the SPIN2 interpreter isn't held in ROM, it becomes just like any other PASM2 program.

evanh · 2021-10-05 01:33

@"Bob Drury" said:
The atached code seems to work by setting PTRB in the program, but if I remove MOV PTRB,##PTRB_Stack statement it stills works. I think the reason it still works is PTRB = 0 and the stack is pointing to Hub Ram =0 which would mean the Spin2 code is overwritten and since there is no spin2 code it doesn't matter.

That would be correct. Not advised though, there is a couple of system variables stashed in that general area. Err, rather, the stack will begin to overwrite the hubRAM copy of your program. I forgot, COGINIT loads PTRB with address of your program in hubRAM.

Bob Drury · 2021-10-05 02:30

Thanks for reply. I believe what you are saying is that PTRB somehow when cogStarted_COGEXEC_NEW := COGINIT(COGEXEC_NEW,@CallProgram,$FFFF_FFFF) is executed
PTRB is loaded with @CallProgram address and PTRA is loaded with $FFFF_FFFF. I have not seen anything to suggest this other than a cryptic message says " PTRB code pointer passed from COGINIT". I started a new chat on this and AJl has some info.

1) Do you know where in the literature this is documented?
2) What is the concept behind loading PTRB with the Subroutine start address? (@CallProgram in the above code)

Regards and Thanks (Boy I am learning how little I know)
Bob (WRD)

Cluso99 · 2021-10-05 02:37

@"Bob Drury" said:
Thanks for reply. I believe what you are saying is that PTRB somehow when cogStarted_COGEXEC_NEW := COGINIT(COGEXEC_NEW,@CallProgram,$FFFF_FFFF) is executed
PTRB is loaded with @CallProgram address and PTRA is loaded with $FFFF_FFFF. I have not seen anything to suggest this other than a cryptic message says " PTRB code pointer passed from COGINIT". I started a new chat on this and AJl has some info.

1) Do you know where in the literature this is documented?
2) What is the concept behind loading PTRB with the Subroutine start address? (@CallProgram in the above code)

Regards and Thanks (Boy I am learning how little I know)
Bob (WRD)

1) Probably in the spin2 document under coginit
2) So you know where the loaded code resides - use is up to the programmer

PTRA is also loaded in pasm if the immediate instruction before cogstart is a SETQ ##somePTRAvalue

Dave Hein · 2021-10-05 02:40

If the COGINIT is preceded by a SETQ it will set PTRA to the value specified by the SETQ.

evanh · 2021-10-05 02:47

These are hardwired in the COGINIT instruction, not a Spin feature. Documented in the instruction spreadsheet - https://docs.google.com/spreadsheets/d/1_vJk-Ad569UMwgXTKTdfJkHYHpc1rZwxB-DcIiAZNdk/edit?usp=sharing

Bob Drury · 2021-10-05 02:54

I see in the instruction sheet " COGINIT {#}D,{#}S {WC} Start cog selected by D. S[19:0] sets hub startup address and PTRB of cog. Prior SETQ sets PTRA of cog."
So "sets hub start up address" must pass control from hub spin to PASM program and "sets hub startup address and PTRB of cog" is interpreted as sets PTRB the same address
as the start up address (@CallProgram in the above code). Definitely will add this to Coginit spin description. This information COGINIT {#}D,{#}S is for PASM but apparently applies to the spin2 command.(a little cryptic) Please let me know if going down the right track.
Regards and Thanks
Bob (WRD)

evanh · 2021-10-05 03:13

Yep, that instruction is the only way to start/restart a cog. So it's going to dictate to a degree.

Also, the Spin COGINIT() function is intended for starting a pasm task in a fresh cog. So it's really a Pasm environment, just launched from Spin. COGSPIN() is function for starting a fresh cog with spin task.

AJL · 2021-10-05 04:53

Also, as noted in the other thread

From the COGINIT section of the 'Parallax Propeller 2 Documentation':
S/# = address This value is either the hub address from which the target cog will
load from, or it is the cog/hub address from which the target cog
will begin executing at, depending on D[5]. This 32-bit value will be
written into the target cog's PTRB register.