ColdFire/68K Microcontrollers and ProcessorsのトピックRe: Problems with 'bit set' operation on the MCF52233

Problems with 'bit set' operation on the MCF52233

Eqqman — Sun, 19 Apr 2009 07:06:09 GMT

Hello-

I'm trying to replace some of the macros that get created by the MCF52233 compiler with atomic operations. For example, I'm using things like

MCF_PIT0_PCSR |= 1

But this compiles into numerous instructions. I need to be able to set this bit in a single instruction. Looking through the instruction set, I see that subq, addq, and bset all have the same allowable format of '#<data>,<ea>x'

So if I try to compile

subq #1, 40000000

addq #1, 40000000

everything is fine, but if I compile

bset #1, 40000000 or

bclr #1, 40000000

I get a compile error 'illegal addressing mode'. So it is not clear to me why this same mode works for some commands and not others when they all allegedly accept it.

Re: Problems with 'bit set' operation on the MCF52233

bkatt — Mon, 20 Apr 2009 20:56:55 GMT

Eqqman wrote:

...if I compile
bset #1, 40000000 or
bclr #1, 40000000

I get a compile error 'illegal addressing mode'.

The tables provided with the full documentation of BSET and BCLR show that combination of addressing modes is NOT permitted. A register must be involved, either the bit number in a source register, or the destination in a data register or through an address register.

To atomically set/clear a bit at a byte address, you can put the bit number in a register, e.g.:

moveq #1,r0

bset.b r0,40000000

Or the address in an address register:

lea 40000000,a0

bset.b #1,(a0)

If the target location is 32 bits, you can use "and" and "or" instructions to make atomic changes with the mask/value in a source register. For a 16-bit I/O port, I don't think atomic is possible with coldfire.