FlexProp: Inline PASM doesn't like 'rdlong Var, #@clkfreq', is this expected?

Francis Bauer · 2024-11-06 07:34

The following simplified example code works fine in PNUT and Prop_Tool, but FlexProp complains about hub memory access from within Inline PASM, but does work in a PASM cog. I assume that this is expected, but I haven't found any mention about this limitation.

con { timing }

  CLK_FREQ = 200_000_000                            ' system freq as a constant
  _clkfreq = CLK_FREQ                               ' set system clock

pub main() | cog

  ipasm()                                           ' start inline PASM
  cog := coginit(cogexec_new,@pasm,0)               ' start PASM cog
  waitms(5)
  cogstop(cog)                                      ' stop PASM cog
  debug("main() finished")

pub ipasm | freq
  debug("Debug start: ipasm()")
  freq := clkfreq
  debug("Spin Clock Freq: ",udec_long_(freq))
  org
    rdlong  pr2, #@clkfreq                          ' get current clock frequency of cog
    'mov pr2, freq
    debug("PASM Clock Freq: ", udec_long_(pr2))
  end
  debug("Debug end: ipasm()")

dat
      org
pasm  debug("Debug start: pasm()")
      rdlong cfreq, #@clkfreq
      debug("PASM Clock Freq: ", udec_long_(cfreq))
      ret

cfreq long 0

When I do a 'Compile & Run' I get the following error:

"C:/flexprop-6.9.10/bin/flexspin" -2 -l --tabs=8 -D_BAUD=230400 -O1  -gbrk  --charset=utf8 -I "C:/flexprop-6.6.2/include"  "C:/Experiments/ClkFreq.spin2"
Propeller Spin/PASM Compiler 'FlexSpin' (c) 2011-2024 Total Spectrum Software Inc. and contributors
Version 6.9.10 Compiled on: Jun 19 2024
ClkFreq.spin2
C:/Experiments/ClkFreq.spin2:20: error: Variable __clkfreq_var is placed in hub memory and hence cannot be accessed in inline assembly
C:/Experiments/ClkFreq.spin2:20: warning: Using # on registers in inline assembly may confuse the optimizer
child process exited abnormally
Finished at Tue Nov  5 18:48:53 2024

evanh · 2024-11-06 10:02

That probably should get fixed in Flexspin. What I've done in the past is store a copy of its address.
eg:

dat
                org
pasm            debug("Debug start: pasm()")
                rdlong pa, clkfrqadr
                debug("PASM Clock Freq: ", udec_long_(pa))
                ret

clkfrqadr       long @clkfreq

Rayman · 2024-11-06 11:14

Isn’t clkfreq actually $14 or something?
Maybe just use that?

Think the general rule is that all variables have to be local…

evanh · 2024-11-06 12:54

@Rayman said:
Isn’t clkfreq actually $14 or something?
Maybe just use that?

Bad idea. The symbol's address is not agreed upon ... and could even be shifted in the future.

PS: Chip did at one point agree to change Pnut/Proptool to use address $14 but it never happened.

FlexProp: Inline PASM doesn't like 'rdlong Var, #@clkfreq', is this expected?

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