explaination of PUB end

ksam

I know it is probably pretty simple, but could someone explain how PUB end works exactly?
I'm having a hard time with
if cog
cogstop (cog ~ -1)

I'm probably reading too much into it

Mike Green

What do you mean by PUB end?

You posted a pretty typical bit of code to stop an I/O driver's cog where the cog # + 1 is kept in a variable called cog. Read the description of COGNEW and COGSTOP and read the description of the unary post-fix "~" operator which is used to zero the variable cog after its value is used for the expression.

ksam

This was out of the propeller fundementals lab book in an example using a start and a stop method. I didn't want to go any further until I knew exactly what it meant. Is the -1 just to keep the value in cog non - zero?

jazzed

Normally a PUB start will have cog := cognew(@PASM, @Parameters) + 1.
The cognew method can return 0 to 7, so 1 is added there. Then in PUB stop, one will only cogstop if cog is non-zero.
If cogstop(cog~ -1) is run, then the cog identifier or cognew return +1 from PUB start is used to stop the cog and the ~ will set cog back to zero.

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--Steve


Propalyzer: Propeller PC Logic Analyzer
http://forums.parallax.com/showthread.php?p=788230

Mike Green

The start method adds one to the value returned by COGNEW/COGINIT so a cog start failure returns zero and success returns a value > 0. The stop method subtracts one to yield the actual cog number. Read the description of COGSTOP and COGNEW.

ksam

Thanks for the help. The post-clear was what was throwing me off. It sets cog back to zero after the operation.

Thanks