Propeller Tool ASM CON byte breakdown Request (or maybe there is a trick I don'

Timothy D. Swieter · 2010-03-03 11:02

While working on some driver code I came across something that could be valuable in the ASM compiling. In the CON section I have many, many, many definitions. For example _S0_MR = $0400. Now, I can't use this definition in ASM because obviously it exceeds $1FF. (For those that aren't familiar with ASM the second register has to be 9 bits or less). So because _S0_MR is larger than $1FF I can't do the following.

mov reg, #_S0_MR

But I would like to be able to do soemthing without breaking all the definitions down since the definitions are what are described in the data sheet. I was thinking I would try the following, but it doesn't compile. Maybe something like this already exist, but if it doesn't maybe it could get added in the compiler?

mov reg, #_S0_MR.byte[noparse][[/noparse]0]
shl   reg, #8
or    reg, #_S0_MR.byte

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

heater · 2010-03-03 11:16

How about:

CON

big_constant = 1234

PUB start

DAT
                  MOV   somewhere, big_constant_dat

somewhere            LONG 0
big_constant_dat  LONG big_constant

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Timothy D. Swieter · 2010-03-03 11:19

heater - won't your method take away from the 496 longs of the cog? I'd hate to have to redefine all the CONs as DATs.

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

heater · 2010-03-03 11:30

Yes, and so does yours with the SHL and OR instructions.

Except the way I have shown only uses one instruction for each reference to the constant in your PASM.

I'm not sure there is any way to load a long constant without consuming the LONG for it.

By the way .byte[noparse][[/noparse] 0 ] and .byte[noparse][[/noparse] 1 ] etc aren't really necessary as you can always use SHIFTS and ANDs when loading a constant:

MOV low_byte, big_constant & $FF
MOV high_byte, (big_constant >> 8) & $FF

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For me, the past is not over yet.

Post Edited (heater) : 3/3/2010 11:35:40 AM GMT

Timothy D. Swieter · 2010-03-03 11:35

Ah-Ha!!! Thanks heater for engaging in the discussion with me. Your last statement is what I didn't realize. I can do the following for the moment and then contemplate the savings/expense of doing redefines in the DAT section.

              mov       reg,    ((_S0_MR >> 8) & $FF)
              shl       reg,    #8
              or        reg,    (_S0_MR & $FF)

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

Cluso99 · 2010-03-03 12:41

heater's method is what I use. It uses 1 less cog long than your method Timothy, and it is actually more readable.

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heater · 2010-03-03 13:04

On can always just define constants as DAT items and forget about having them in a CON section at all.

This has two advantages:
1) Large constants in DAT are available for use in both Spin and PASM automatically.
2) Makes the program smaller when using large constants.

The following code goes from 17 program LONGs to 11 if I change the start method to use the "b" constant in DAT rather than the "a" constant definition.

CON

a = $12345678

VAR
long num1
long num2
long num3
long num4
long num5
long num6
long num7
long num8
long num9

PUB start
  num1 := a
  num2 := a
  num3 := a
  num4 := a
  num5 := a
  num6 := a
  num7 := a
  num8 := a
  num9 := a

DAT
b long $12345678

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For me, the past is not over yet.

Timothy D. Swieter · 2010-03-03 13:26

I am glad I asked, it always pays to ask because I learn something in the process.

Heater, with your last example, what is it about the way that SPIN handles a CON vs a DAT that causes 6 less longs?

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

Timothy D. Swieter · 2010-03-03 13:29

Maybe I answered my own question. From studying the Hex output it looks like with the CON that it uses the value over and over. With the DAT is references the value once. I also see with the DAT it appears to store the number backwards.

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

Timothy D. Swieter · 2010-03-03 13:35

One disadvantage to having CON in the dat section is that any calling code outside of the file can't use the Object#con construct because it can't get the value out of DAT.

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Timothy D. Swieter, E.I.
www.brilldea.com - Prop Blade, LED Painter, RGB LEDs, 3.0" LCD Composite video display, eProto for SunSPOT
www.tdswieter.com

Bean · 2010-03-03 14:06

You can use

mov reg,#_SO_MR & $1FF 
movd reg,#_SO_MR >> 9

Bean

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Post Edited (Bean) : 3/3/2010 2:11:07 PM GMT

heater · 2010-03-03 14:14

"I also see with the DAT it appears to store the number backwards."

The Prop. is the only architecture + language system I've seen that is both big endian and little endian at the same time.

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VIRAND · 2010-03-03 16:13

heater said...
"I also see with the DAT it appears to store the number backwards."

The Prop. is the only architecture + language system I've seen that is both big endian and little endian at the same time.

interesting... might explain a lot of peculiar results trying to pass dsp-like data between spin and pasm.

I also assume that CON was not assigned any memory but merely put labels on constants used during
compile time, but obviously if a label is used more than once it would be part of each instruction
that used the same labeled constant.

DAT still seems hard to accurately find and point to when used as data storage, with labels there not
easily evaluated consistently, and @ tending to always miss them by 16 or some random number. Has
it ever been conveniently solved to determine the address of a label in DAT? I seem to invent a lot of
wheels every time I need to access DAT space, and I just thought of searching HUBRAM for strings at
the beginning of DAT such as "DAT0", but that makes a long, which you say the endianness is not
consistent, so longs like $F000000F and $FF0000FF would might work as palindromes but may not be
unique and rare enough to use, like $F5A00A5F or $B0DA_AB0D. (Which a small loop would search
for and when found, result in a reliable pointer to a DAT block in both spin and pasm). What method
is simpler than such contrivances and also consistent?
edit: endianness in longs can be so variational that this new strange way might require them to be
more like $FF0000FF and $00FFFF00 until they are exactly specified, with those two non-unique
examples possibly being the only generally valid ones until it is known how they are stored in
every possible case. When, if ever, does a long or a string appear backwards or mixed up in DAT
if it is used or changed by both spin and pasm? I only noticed this problem with the internal font
before, and assumed that only the video generator was shifting the less obvious way.

Post Edited (VIRAND) : 3/3/2010 4:34:20 PM GMT

Phil Pilgrim (PhiPi) · 2010-03-03 17:10

I use this if I want the constant accessible to the outside and/or visible near the top of my code:

CON

  MY_BIG = 1234567

PUB start

...

DAT

...
        mov     reg,_my_big

...

_my_big long    MY_BIG

It takes no more room than the movs/movd tango and is quicker to execute and more readable. (I typically write constant labels using all caps to distinguish them from variables.)

For plain numeric constants that don't need a descriptive name, I use something like this:

        mov     reg,_0x0012_34cd
        mov     reg2,_512

...

_0x0012_34cd long $0012_34cd
_512         long 512

-Phil

Post Edited (Phil Pilgrim (PhiPi)) : 3/3/2010 5:18:43 PM GMT

Propeller Tool ASM CON byte breakdown Request (or maybe there is a trick I don'

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