[Flashforth-devel] building larger program words -- arduino mega2560 FF5

[craig b. <dab...@ya...>]

Hi again,

    As usual I'm trying to do something in Forth that may be slightly insane.  We need to do simultaneous testing of some SHT31 Temperature/Humidity sensors in an environment chamber.  They're I2c interfaced and all have the same buss address.  And they handed me a 'Duino Mega 2560...  Of course I said "FlashForth! I've been bit-banging I2c since the early '90-s, how hard could it be?".

    Well building the pieced was pretty smooth, basic I2c Master comes down to 6 routines that can be combined to do pretty much everything you need.  These sensors want to be written a 2 byte command, given a millisecond to do their thing, and read out a 6 byte data packet.  Simple enough, and all of the parts work just fine.  I use  a single port for 4 clock lines, 4 data lines, and a ram value system to change which line pair gets used at any given time.  No problem till I try to roll the whole sequence into something that can run as a program and spew data till the environmental chamber boils over.  Then it blows up, the delay between operations disappears, and communication breaks down.

    I'm an old PIC programmer and not really well informed about ATMEGA internals.  I'm guessing that somewhere a stack overflows, a system variable gets clobbered, or a branch instruction gets compiled in that winds up crossing some boundary it shouldn't...  Or something else.  

(Oh and just for reference I'm running the most recent  2560-16MHz-38400.hex  out of the box on an old-school Arduino brand Mega2560...  and according to my 'scope "ms" is running over 20x slower than it advertises.)

    I noticed oddly similar things in PIC18 FlashForth, but I was playing around in the interrupts as well.  I understand the PIC assembler well enough to make some good guesses about what needed restructured.

    If anyone has any pointers to offer about how to build larger convoluted routines to run for hours (or days), I could use some ATMEL insights on what to look for.   Any guesses about what pit (hiding in my blind spot) I might be tripping into would be greatly appreciated.
 
Thanks for your attention,
craig bair

OBTW: Why does the spellcheck want to replace "atmel" with "oatmeal"?