Atomic Operation
David Williams
davidwilliams@ozemail.com.au
Sat Oct 2 18:15:00 GMT 1999
Hi All,
A while ago I got some help to implement some atomic operation using
constraints within inline assembler. I now need to do a similar thing but
it got complicated. After some trial and error I got the following bit of
code to produce the desired assembler - but it seems quite messy. My
question is there a better way to produce the same result?
asm(" move.L %0,%%d0" : : "m" (InpMasks[digChan]) : "%%d0");
asm(" OR.L %%d0,%0" : "m=" (EZ328_IMR) : : "%%d0");
Note: InpMasks[digChan] references a 32 bit value from an array of 32 bit
values. EZ328_IMR is memory address of 32 bit hardware register (interrupt
mask register in this case).
What I am trying to do is use the OR instruction on a memory address. GCC
seems to prefer to do it in registers and then transfer the result to
memory. This is no good for atomic OR on hardware register. So I devised
the above assembler. The OR instruction requies that one of the operands be
a data register so I had to preload a data register. Then I had to specify
the register I loaded in the first instruction in the second. To ensure
that it does not clash with other register usage in the function it is used
in I specify the data register as being "clobbered" (last argument in the
asm statement). The selection of the data register to use is arbitrary.
Would I be wiser to use any particular data register and why?
TIA
David Williams.
davidwilliams@ozemail.com.au
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