8-bit MicrocontrollersのトピックRe: Software SPI Assembly

Software SPI Assembly

mjcoury — Wed, 13 Sep 2006 01:57:42 GMT

I pulled this code straight from a Freescale app note AN991.pdf Page 12... modified slightly...

asm{
LDA #$08
STA iBitCounter // Set bit counter
AGN:
BRSET 7,PORTA,* // Wait for Falling Edge of Clock Pin 7 of Port A
//ROL RES1 // Shift data to send
//BCS SET1 // Check data status
//BCLR 6,PORTC // If 0, clear data out
BRCLR 7,PTAD,* // Wait for Rising Edge of Clock Pin 7 of Port A
BSET 7,PTBD
BRSET 0,PTCD,STR // Check input data status
STR:
ROL *cSPIData_ptr // Store in result
DEC iBitCounter // Check for end of byte
BCLR 7,PTBD
BNE AGN
}

It doesn't compile in CW version 3.1 and I am assuming it has something to do with the '*'

First Error is C18103: Factor Expected highlighting the first line...

then

C18101: Object is not a field which again points to a line with a '*'

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Re: Software SPI Assembly

bigmac — Wed, 13 Sep 2006 02:48:10 GMT

Hello mjcoury,

The use of the asterisk (*) as a branch destination works OK for assembler, but apparently not for in-line code.

However, it can easily be avoided by defining a label prior to each bit test and branch instruction, and then branching to that label within the instruction.

AGN:
BRSET 7,PORTA,AGN // Wait for Falling Edge of Clock Pin 7 of Port A

I wonder if the following line is OK for inline assembly - it certainly would be problematic for standard assembler.

ROL *cSPIData_ptr // Store in result

Regards,

Mac

Re: Software SPI Assembly

CompilerGuru — Wed, 13 Sep 2006 06:21:51 GMT

Actually I think the * works as branch target, but it does definitely not work for the "ROL *cSPIData_ptr".

Daniel