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Bug in MPLAB C18 port

Posted by Dewey on July 28, 2005

I have discovered a bug in the MPLAB C18 port that affects things stored in program memory (using the rom qualifier). Things stored in program memory require table operations to retrieve, which makes use of the 21 bit TBLPTR register (which uses 24 bits). Unfortunately, the C18 compiler generated assembly only sets bits 0-16 of the TBLPTR register anytime it needs to set up an address to access program memory. The port.c file sets TBLPTRU to 0x77 when initializing the task context. When that value is restored to the 17-24 bits of TBLPTR, it never gets overwritten by compiler generated code, thus, all program memory operations do not behave correctly. The fix is to set the TBLPTRU to 0x00 when initializing the task context in the pxPortInitialiseStack function of port.c.

RE: Bug in MPLAB C18 port

Posted by Richard on July 28, 2005
Good info - thanks. I will add this to the 'known issues' list on the downloads page.

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