Weird cog starting issue

Gregg Harrington

Hello everyone,

I have found a problem (and the solution), but don't understand what is going on. I am writing a system that uses multiple cogs to manage some state. I start these cogs in the beginning and go about my business. However, I noticed one of the cogs was not starting (using a blinking LED in each cog method for testing).

After hours of testing poking and proding, trying different propellers, different code files I finally found out the problem to be a var section in my code. Here is the var section that works:

VAR
byte mode
byte newModeRequest
byte file_buf [13]
byte file_content[128]
byte xbeeCog
byte xbeeMonitorStack[500]

This one does not work and the cog fails to start entirely!

VAR
byte mode
byte newModeRequest
byte file_buf [13]
byte file_content[128]
byte xbeeMonitorStack[500]
byte xbeeCog

Please note: the only different between these two sections (and weather or not it works or doesn't) is the order of my last two variable declares.

I tried to reproduce this other ways, but as long as the variables were in the right order, it worked.

Anyone every run into something like this?

Thanks,

Gregg

John Abshier

My guess is that you are putting more than 500 bytes in xbeeMonitorStack and stepping on xbeeCog.

John Abshier

MagIO2

Looks like an alignment problem for me. Stacks are LONG and you should define it as long! If you fire up the COG with a stack-address that's not long alligned, the variable(s) in front of the stack will be the stack base.
So in your case the xbeeCOG and the really used stack-address are the same. My guess is that you do something like

xbeeCOG := COGNEW( xxx, @xbeeMonitorStack ) + 1

So, as xbeeCOG is equal to the first position of the stack this assignment will overwrite your stack. Don't know what this means for the new COG.

MagIO2

PS: In bed I had the following idea to proof my theory. Use the not working order of VARs and change the COGNEW which uses the xbeeMonitorStack like this

.. COGNEW( ..., @xbeeMonitorStack + 3 )

Gregg Harrington

MagIO2, wonderful! Thank you, I truly thought I was going crazy! I was totally confused there for a while!!! That makes total sense now.

Cheers,

Gregg