topic Re: test CCR register/ assembler macros in S12 / MagniV Microcontrollers

test CCR register/ assembler macros

grzegorzK — Fri, 04 Nov 2011 19:12:18 GMT

I have problem: I would like to find out if function is called from ISR or from main task context. I am not sure if it possible at all, but if I do not use nested interrupts than is enough for me to test if global maskable interrupts are masked or not, it is flag I in CCR register.

I wrote code but I am not sure if is correct, because I do not know how to use assembler with C code, may some one check:

uint8_t CC;
static uint8_t const BIT_I = 0x10;

__asm(pshc);
__asm(movb 1, SP+,CC);
__asm(DES);
__asm(pulc);

if (CC & BIT_I)
{
/* I flag is set */
}

issue for me are assembler macros, may someone looke at this macros if are they correct or there is easier soultion to read CCR register (maped to global memory?)?

Regards

/Greg

Re: test CCR register/ assembler macros

kef — Fri, 04 Nov 2011 21:39:22 GMT

These two lines should suffice

__asm(pshc);

__asm(movb 1, SP+,CC);

Or without stack manipulations, just

TFR CCR, A

STAA CC

It doesn't make sense to allocate BIT_I constant in flash. Better define it either as

#define BIT_I 0x40

enum {BIT_I=0x40};

Re: test CCR register/ assembler macros

grzegorzK — Mon, 07 Nov 2011 16:06:11 GMT

Thank you

kef wrote:

It doesn't make sense to allocate BIT_I constant in flash. Better define it either as
#define BIT_I 0x40
or
enum {BIT_I=0x40};

why it does not make sense? I do not understand.

Re: test CCR register/ assembler macros

kef — Mon, 07 Nov 2011 16:48:30 GMT

Because it's 1) a waste of 1 byte of flash memory to store BIT_I constant, and 2) code is slower. Instead of using immediate addressing (BIT_I constant embedded in CPU instruction and effectively queued in instruction queue), you are forcing CPU to read BIT_I from memory. This is much slower and thus doesn't make sense.