Propeller Tricks & Traps (Last update 21 June 2007)

Phil Pilgrim (PhiPi) · 2007-06-20 05:52

Right you are on both counts. Good eye! I've made the requisite changes to the document in the first post.

Thanks!
Phil

mpark · 2007-06-20 13:56

I'm glad that's straightened out, but now the example hardly seems to be about indirect JMP at all. Perhaps it would be more compelling if it used an explicit state variable?

Init         MOV State,#State1
'            NOP <- no longer needed, I guess
             JMP State
State1       do state1 stuff
             ..
Common       common post-state code
             ..
             JMP State

State        RES 1

Post Edited (mpark) : 6/20/2007 2:22:00 PM GMT

Phil Pilgrim (PhiPi) · 2007-06-20 17:50

Yeah, I thought about that, too, as I was posting the error correction. But I was in such a hurry just to fix it that I didn't follow through with the tighter, more illustrative code. That has now been remedied.

Thanks for the prodding!

-Phil

mpark · 2007-06-21 07:00

One more thing while I have your attention: The last trick, on sign-extension, says

In Spin, do this:
Value := Value << 24 ~> 24

Wouldn't it be more idiomatic to do this instead:

~Value

I know the trick is about sign-extending from any bit, but using a byte as an example made me half expect that the trick would be the ~ operator. (Of course, for C/C++ guys, this meaning of ~ may be more of a trap than a trick.)
Perhaps the text could mention the two sign-extension operators ~ and ~~, then describe the left/right shifty trick for arbitrary sign bit positions, with an example that uses an oddball shift count rather than 24 or 16. It could also mention that execution time is independent of shift count, assuming that's the case, which I believe it is.

Phil Pilgrim (PhiPi) · 2007-06-21 17:42

'Another good suggestion, which I've now incorporated.

You're right about the execution time of the shifts. The Propeller uses a barrel shifter, rather than an incremental one. However, since this is neither a trick nor a trap, there wasn't a good place to incorporate such info in the document.

Thanks,
Phil

mpark · 2007-07-03 07:44

A trick suggestion: I thought the use of jmpret as a task dispatcher in tv_drv was pretty darn clever. Some coroutine action going on there.

A trap suggestion: Square brackets mean array indexing -- except when they don't. After INA, DIRA, etc., they are pin specifiers. I just find that sort of special-case hijinx annoying (probably just me).

Fred Hawkins · 2007-07-04 05:32

mpark said...
....·Square brackets mean array indexing -- except when they don't. ...

A nice list would summarize all the various parentheticals (and where they are used) be they (), [noparse]/noparse or what have you. The compiler sure does (expletive) obscurely when you·get them wrong...

Mike Green · 2007-07-21 14:52

The COGNEW/COGINIT Spin statements allow an arbitrary Spin method call as the first parameter including a call of a method in another object (like foobah.myMethod). This is accepted by the compiler without comment, but will not be executed properly. The method must be one in the same object as the COGNEW/COGINIT call.

Jasper_M · 2007-08-25 17:00

2 traps:

values in DAT section byte etc. are not range checked (1.05.5):


DAT 
byte $555

will silently fail, and it's equivalent to byte $55.

EDIT: I couldn't replicate the following trap when I tried with simple code...

x := 1 + y

will first write 1 into x, then add y to that.
So if you have an assembly driver polling for that location, it will see it when it's 1. eg. I had hard time debugging the following code:

    s_ras_cmd := const#CMD_SAVE_MAP + p_tilemap_index

The following works:

    x := const#CMD_SAVE_MAP + p_tilemap_index
    s_ras_cmd := x

Post Edited (Jasper_M) : 8/25/2007 5:51:06 PM GMT

Jasper_M · 2007-08-25 17:46

Your code has a bug, rdlong RA, opflag WZ reads address 0 in hub ram. you should pass a pointer of opflag in PAR etc. EDIT: A post got deleted between my messages.

I wrote some test code, but now I can't even replicate the bug myself... but the temporary variable really solved the problem

deSilva · 2007-08-25 17:51

Sorry, Jasper, I was unsure for a second.. No, my program is fine

But I cannot produce your bug

{
 Exploring JASPER's Bug  v04
 2007 deSilva 
}
CON

  _clkmode = xtal1 + pll8x
  _xinfreq = 10_000_000
     
OBJ
  pc   :       "PC_Interface"  ' Ariba's PropTerminal
  
PUB main
  pc.start(31,30)

  alarm := @alarm
  opflag := @opflag
  cognew(@asm,0)

  
  repeat
    pc.out(0) 
    pc.str(string("checking JASPER's trap ...press any key"))
    if alarm
       pc.str(string(13, "There's a fly in the ointment"))
       waitcnt(clkfreq+cnt)
       alarm := 0 

    if pc.gotKey   ' press a key to show the bug (?)
      pc.clearKeys
      ' according to the report, first 0 should be written to opflag
      opflag := 0 + takeYourTime 
    waitcnt(clkfreq/20+cnt)

pri takeYourTime
    waitcnt(clkfreq/1000+cnt)
    return 1  ' change this to 0 and the programm will trigger...
        
DAT
    org    0
asm
    ' Wait for opflag ==0
    rdlong RA, opflag  WZ
    if_Z   wrlong  opflag, alarm  'write any value as long as its not 0  
    jmp    #asm
  RA       long 0 
  alarm    long 0
  opflag   long 0

Post Edited (deSilva) : 8/25/2007 11:45:37 PM GMT

Jasper_M · 2007-08-25 20:25

EDIT: POST REMOVED : D I just didn't read the whole code, there¨s nothing wrong with it.

Post Edited (Jasper_M) : 8/25/2007 8:34:02 PM GMT

deSilva · 2007-08-25 21:38

There was no good countercheck in the program, I tried this, and it triggers:

  if pc.gotKey   ' press a key to show program works
      pc.clearKeys
      ' countercheck
      opflag := 0
      opflag := 1

... and I finally found the "bug" in it: It has to be "ointment" not "oinment" - idiot that I am.

Post Edited (deSilva) : 8/25/2007 11:43:10 PM GMT

hippy · 2007-09-21 20:38

A trick for saving stack space is to use the 'result' variable associated with each method, whether it returns a result or not. A benefit is that unlike other local variables it is zeroed on entry to the method.

If using a variable named 'result' isn't appealing, it can be renamed as the return variable ...

PRI MySub : tmp

Phil Pilgrim (PhiPi) · 2007-09-28 19:22

I've corrected an error on page 8, where it stated that bits 31..2 are passed to the PAR register by COGNEW. Actually it's bits 15..2. My thanks to Rayman and BradC for pointing this out!

At some point I need to collect and filter the latest batch of user-contributed material for inclusion. I haven't forgotten, and thanks for all the input!

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 9/28/2007 7:29:43 PM GMT

LewisD · 2007-10-09 21:01

Hi Phil,

I was talking with Chip about the Turboprop and ran into something new.(I think)
My discussion was in “What would you want more of, cogs or RAM?” starting on page 25.
I'm still looking to see if all 512 COG RAM location are indeed filled with HUB data during initialization.
This would be the easiest way to get code/data into the 'Shadow Registers'.

LewisD

Chip said...

Cog RAM is read directly for instructions, not special 'source' registers such as PAR, CNT, etc. So, you could write a JMP instruction into the PAR register ($1F0) and have it execute, not having to consider what PAR would return as a 'source'. In other words, the large-model would work fine by reading eight contiguous hub longs into $1E8-$1EF and then JMPing to $1E8, and then having a JMP back execute from RAM (not PAR) at $1F0.

Chip how many of the registers are like that?(all?)

Yes, all. Some registers like PAR, CNT, INA, etc. have special mux's for reading live states when accessed as source registers. All instructions and destination registers are read from RAM, though - not mux's.

Would the code look like this to stuff $1f0?

mov $1f0,stuff
...
...
stuff jmp next-page

That's it.

deSilva · 2007-10-09 21:32

@LewisD: You are mixing here some things that do not belong together. What Chip was saying is correct to the point but not what you insinuate...

deSilva · 2007-10-17 17:34

A SPIN REPEAT trap, well known, but sometimes forgotten...

  st := 0
  REPEAT i  FROM  st TO 1
       ' executed twice  (i = 0,1)

  st := 2
  REPEAT i  FROM  st TO 1
       'also executed twice  (i  = 2,1)

SPIN evaluates both limits in the beginning and decides whether to run the loop forward or backward. This is a great feature, but extremely surprising for experienced programmers.

Post Edited (deSilva) : 10/17/2007 5:39:23 PM GMT

Beau Schwabe · 2007-10-20 07:19

Since _XINFREQ and _CLKFREQ are mutually exclusive, meaning you can only use one or the other, but·not both in a CON block.

Here is a trick that·allows you to·calculate·_CLKFREQ·within the CON block while·using _XINFREQ...

[b]CON[/b]
  [b]_CLKMODE[/b] = [b]XTAL1[/b] + [b]PLL16X[/b]
  [b]_XINFREQ[/b] = 5_000_000 
  clockfreq = (([b]_CLKMODE [/b]- [b]XTAL1[/b]) >> 6) * [b]_XINFREQ[/b]

Likewise, here is how you can calculate·_XINFREQ within the CON block while using _CLKFREQ...

[b]CON[/b]
  [b]_CLKMODE[/b] = [b]XTAL1[/b] + [b]PLL16X[/b]
  [b]_CLKFREQ[/b] = 80_000_000
  Xinfreq = [b]_CLKFREQ[/b] / (([b]_CLKMODE [/b]- [b]XTAL1[/b]) >> 6)

A situation where this might be useful would be to setup timing constants within the CON block without resorting to using any variables.

[b][b]CON[/b]
  [b]_CLKMODE[/b] = [b]XTAL1[/b] + [b]PLL16X[/b]
  [b]_XINFREQ[/b] = 5_000_000 
  clockfreq = (([b]_CLKMODE [/b]- [b]XTAL1[/b]) >> 6) * [b]_XINFREQ[/b]
 
[/b]
  _1uS  = clockfreq / 1_000_000 'Divisor for  1 uS
  _10uS = clockfreq /   100_000 'Divisor for 10 uS
  _1mS  = clockfreq /     1_000 'Divisor for  1 mS
  _1S   = clockfreq /         1 'Divisor for  1 S

[b]PUB[/b] Pause_1uS(Period)                                    '1 uS 
    [b]waitcnt[/b](_1uS * Period + [b]cnt[/b])

[b]PUB[/b] Pause_10uS(Period)                                   '10 uS 
    [b]waitcnt[/b](_10uS * Period + [b]cnt[/b])

[b]PUB[/b] Pause_1mS(Period)                                    '1 mS 
    [b]waitcnt[/b](_1mS * Period + [b]cnt[/b])

[b]PUB[/b] Pause_1S(Period)                                     '1 S 
    [b]waitcnt[/b](_1S * Period + [b]cnt[/b])

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 10/20/2007 8:32:11 PM GMT

Timothy D. Swieter · 2007-10-20 08:01

Excellent suggestion Beau! I think I will use this method in the future. Not only does it eliminate some variables, but it also saves the execution time where other routines do the calculation each time to determine the correct delay length.

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Timothy D. Swieter
tdswieter.com

One little spark of imagination is all it takes for an idea to explode

hippy · 2007-10-20 13:19

It would be nicer if the Propeller Tool could (1) create a _CLKFREQ or _XINFREQ based on the other (2) allow both _CLKFREQ and _XINFREQ and produce an error only if the two do not match up using the _CLKMODE setting.

Ken Peterson · 2007-10-21 02:35

might be a trap if you change clock modes within your program..

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The more I know, the more I know I don't know.· Is this what they call Wisdom?

deSilva · 2007-10-21 09:57

It's a trap anyhow when you forget to change the byte at adress #0

deSilva · 2007-10-27 10:32

Trap AND Trick: Not sure how well this was known before:
The compiler remembers the size of a label in the DAT section according to the size identifier after this label.
Example:

DAT
lo   LONG 10,20,30
by   BYTE  "ABC",0

However a "standalone label" is always considered as a LONG:
Example:

by
    BYTE "ABC",0

is no longer correctly addressable by by[noparse][[/noparse]...]

There is a work around as follows

by  BYTE
    BYTE "ABC",0

A size identifier without preset does not allocate space but assigns the correct attribute to the label only!

It most likely also aligns for WORD and LONG, but I have not checked it.

Post Edited (deSilva) : 10/27/2007 10:37:32 AM GMT

mpark · 2007-10-27 11:05

deSilva said...

However a "standalone label" is always considered as a LONG:

But, strangely enough, the compiler complains if you say "standaloneLabel.long[noparse][[/noparse]...]"

(See also http://forums.parallax.com/showthread.php?p=682286.)

deSilva · 2007-10-27 11:25

I shall investigate a little bit deeper.. Alas, I do no longer read the Hydra threads..
But I already can assure you it is not BYTE a standalone label defaults to...

mpark · 2007-10-27 16:36

I wasn't disagreeing with you, just adding an additional quirk, but on digging a little deeper it appears that the rules for standalone labels are:
a. The last size identifier preceding a standalone label determines its "type".
b. If there is no preceding size identifier, a standalone label defaults to BYTE.

E.g.:

DAT
long0                           ' defaults to BYTE
        long $1234, $abcd  

PUB Start | ch
  tv.start( 24 )

  tv.hex( long0, 8 )            ' 00000034
  tv.out( 13 )
  tv.hex( long0[noparse][[/noparse] 1], 8 )        ' 00000012
  tv.out( 13 )
  tv.hex( word0, 8 )            ' 20012000
  tv.out( 13 )
  tv.hex( word0[noparse][[/noparse] 1], 8 )        ' 13121110
  tv.out( 13 )
  tv.hex( byte0, 8 )            ' 00001110
  tv.out( 13 )             
  tv.hex( byte0[noparse][[/noparse] 1], 8 )        ' 00001312
  tv.out( 13 )
  tv.hex( long1, 8 )            ' 00000078
  tv.out( 13 )
  tv.hex( long1[noparse][[/noparse] 1], 8 )        ' 00000056
  tv.out( 13 )

DAT
word0                           ' LONG because of LONG in previous DAT section
        word $2000, $2001
byte0                           ' WORD
        byte $10, $11, $12, $13
long1                           ' BYTE
        long $12345678

Post Edited (mpark) : 10/27/2007 4:45:36 PM GMT

deSilva · 2007-10-27 17:10

THAT'S IT! A little bit tricky to find out (advanced debugging)

Congrat!

Phil Pilgrim (PhiPi) · 2007-10-27 17:29

This is where a list file from the compiler/assembler would come in handy.

-Phil

Beau Schwabe · 2007-11-20 16:26

Here is a cool trick using the muxc command to self modify the instruction bits of another command, thus changing the command entirely....
The example uses this technique to Bit-Bang data to an I/O port with 50nS output transitions (20MHz).

Enjoy!

[b]CON[/b]
  [b]_clkmode[/b]      = [b]xtal[/b]1 + [b]pll[/b]16x
  [b]_xinfreq[/b]      = 5_000_000


OutputPin = 0
  DataOut = %1000_1111_0000_1010_1010_1001_1001_1011 '<- Data to send


[b]PUB[/b] ASM_FAST_BitBang_DEMO

    [b]cognew[/b](@FAST_BitBang,0)
   
[b]DAT[/b]


FAST_BitBang  [b]org[/b]       0

              [b]mov[/b]       OutputPinMask,          #1                              '' Create Pin Mask for Output pin
              [b]shl[/b]       OutputPinMask,          #OutputPin

              [b]mov[/b]       LoopCounts,             #32              'Self Modifying Bit-Bang Code
Loop          [b]ror[/b]       Buff,                   #1 [b]wc[/b]            
BitIndex      [b]muxc[/b]      Bit0,                   instr_mux
              [b]add[/b]       BitIndex,               dest_inc
              [b]djnz[/b]      LoopCounts,             #Loop
             
                                                'This section of code self modifies the code below,
                                                'so that each of the bits can transition in only 50nS.
                                                           
                                                'It does this by MUXing the "C" flag into the instruction
                                                'location of the muxz commands below.
                                                         
                                                'By default, the way that the muxz is used, it will make
                                                'output Pin LOW.  When the instruction location is changed...
                                                '...from 011110 to 011111 (<-Notice only one bit difference)
                                                '...in this section of the code via the muxc instruction, 
                                                'muxz below effectively becomes a muxnz.  Cool Huh!?

              [b]or[/b]        [b]dira[/b],   OutputPinMask   'Make Pin an Output

              [b]mov[/b]       [b]outa[/b],   #1 [b]nr[/b],[b]wz[/b]        'Clear Z flag for TRUE data
'              [b]mov[/b]       [b]outa[/b],   #0 [b]nr[/b],[b]wz[/b]        'Set Z flag for INVERTED data
 
                                                                   The following MUX commands use the "Z" flag set above

Bit0          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW      Self Modified Code to Bit Bang at 20MHz
Bit1          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW      
Bit2          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           The lines above that read...
Bit3          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit4          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           muxc {Bit#}, instr_mux
Bit5          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit6          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           ...self modify the instruction bits
Bit7          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           of the lines that read...
Bit8          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit9          [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           {Bit#} muxz outa, OutputPinMask
Bit10         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW            
Bit11         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           ...so that when the BIT in Buff is
Bit12         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           a "1", the lines that did read... 
Bit13         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit14         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           {Bit#} muxz outa, OutputPinMask                                           
Bit15         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit16         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           ...now function as if they read...
Bit17         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit18         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           {Bit#} muxnz outa, OutputPinMask
Bit19         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit20         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           ...with 'muxz' the output pin is made
Bit21         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           LOW ... with 'muxnz' the output pin
Bit22         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           is made HIGH.  This is so that a pin
Bit23         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           can transition in 4 Clocks or 50nS rather
Bit24         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           than 8 Clocks or 100nS. This makes it twice
Bit25         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           as fast.
Bit26         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW           
Bit27         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit28         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit29         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit30         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW
Bit31         [b]muxz[/b]      [b]outa[/b],   OutputPinMask   'Default LOW

instr_mux               [b]long[/b]    $0400_0000
dest_inc                [b]long[/b]    $0000_0200
Buff                    [b]long[/b]    DataOut

OutputPinMask           [b]long[/b]    0
LoopCounts              [b]long[/b]    0

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 11/20/2007 6:26:56 PM GMT

Propeller Tricks & Traps (Last update 21 June 2007)

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