Spin a good fit for the Propeller

Heater. · 2014-09-01 23:50

ErNa,

The only difference to "normal" interrupts is the mechanism to trigger the routine.

Wait a minute.

A function call is nothing like an interrupt diverting CPU attention. A function has parameters an interrupt does not. A function has return values an interrupt does not. A function happens when I want it to not at some random time as I run.

A function call is nothing like a different process running on a different CPU. A function returns a process may not. For example.

Electrodude · 2014-09-02 09:51

ErNa wrote: »

A function call guarantees availability of a result the moment the program, interrupted by the function, resumes.

That makes me wonder. If a cognew'd function returns (stopping the cog), can you find its result somewhere in its stack? This depends on which flavor of anchor is used, so I doubt it will work but will try to find out now.

Phil Pilgrim (PhiPi) · 2014-09-02 10:19

According to my test program here:

CON

  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000


OBJ

  pst : "parallax serial terminal"
  
VAR

  long stack[30]

PUB start

  pst.start(115200)
  cognew(tester, @stack)
  waitcnt(cnt + clkfreq / 10)
  pst.dec(stack[3])
  repeat

PUB tester

  return 1234567

The result is returned on stack[3]

-Phil

Dave Hein · 2014-09-02 10:26

stack[3] is not the return location -- it's just the scratch area on the stack where the value of 1234567 was loaded temporarily. A return value is loaded on the stack only if the calling method requires a return value. This is indicated by a bit in the stack frame. I suspect the default stack frame that is used does not specify loading a return value. You could return a value through the RESULT variable, which is located at stack[2]. The following program demonstrates how that would work.

con
  _clkmode = xtal1+pll16x
  _clkfreq = 80000000

obj
  ser : "FullDuplexSerial"

dat
  stack long 0[20]

pub main
  waitcnt(clkfreq*3+cnt)
  ser.start(31, 30, 0, 115200)
  cognew(sub1, @stack)
  repeat until stack[2]
  ser.str(string("result = "))
  ser.hex(stack[2], 8)
  ser.tx(13)
  waitcnt(clkfreq/10+cnt)

pub sub1
  result := $deadbeef

Electrodude · 2014-09-02 10:48

Cool! I'm still stuck trying to figure out what the RUN (opcode $15 = %0101_01 = j5 nz_and_nc) PNUT bytecode does and how it has anything to do with strcomp.

Phil Pilgrim (PhiPi) · 2014-09-02 10:49

'Interesting, Dave. Thanks for clearing that up.

-Phil

Spin a good fit for the Propeller

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