[Mspgcc-users] returning long

[Peter Jansen]

I have some problem with a function returning a long, which I don't seem 
to be able to reproduce in a simple example.

I have this function defined in aad7789.c
unsigned long ad7789Read(unsigned char ch, unsigned long *data)
{
    unsigned long d;
    unsigned char rx;

    P1OUT &= ~0x01; /* CS */

    /* AD7789 mode single converison, unipolar */

    ad7789ModeWrite(ch & 0x03, 0x86);

#ifdef TARGET
    while ((P3IN & 0x04) != 0); /* Wait for data ready */
#endif

    rx = ad7789StatusRead();

    /* Read the data register */

    ad7789CommWrite(0x38 | (ch & 0x03));

    rx = ad7789SpiTxRx(0xff);
    d = rx;
    rx = ad7789SpiTxRx(0x00);
    d = (d << 8) + rx;
    rx = ad7789SpiTxRx(0xff);
    d = (d << 8) + rx;

    P1OUT |= 0x01; /* CS */

    *data = d;

    return d;
}

and a function calling this from cmd.c

void Ad7789Cmd(void)
{
    unsigned char chan;
    unsigned long data, d;
    char *p;

    p = Line;
    p = GetNextParameter(p); /* find the next param if there is one */

    chan = (unsigned char)stoi(p, 10);

    ad7789PowerUp();
    data = ad7789Read(chan, &d);
    printf("AD7789 data %ld\r\n", data);
    ad7789ShutDown();

    printf("AD7789 d %ld\r\n", d);
}

now the value returned to data seems to be the upper 16 bits of the 
return value, where as d (passed as a pointer) is correct.

The assumbler listing for the above function is

.LM32:
        mov     r4, r15
        add     #llo(6), r15
        mov.b   @r4, r13
        mov     r15, r14
        mov     r13, r15
        call    #ad7789Read
        mov     r15, 2(r4)
        mov     2(r4), 2+2(r4)
        rla     2+2(r4)
        subc    2+2(r4), 2+2(r4)
        inv     2+2(r4)

I don't understand what the last 4 instructions do? and it never uses 
the value returned in r14.

the compile line for ad7789.c are

msp430-gcc -save-temps -DTARGET -mmcu=msp430x149 -g -Wno-main 
-I./include -Ibl/include -Iblbl/include -Iblblbl/include -c 
lib/ad7789/ad7789.c -o lib/ad7789/msp430x149/ad7789.o

and for cmd.c are

msp430-gcc -save-temps -DTARGET -g -Wno-main -mmcu=msp430x149 
-I./include -Ibl/include -Iblbl/include -Iblblbl/include -c 
multiSensor/cmd.c -o multiSensor/msp430/cmd.o

does anyone have any ideas?

--
Peter Jansen
STS
Australian Antarctic Division
Channel Highway
Kingston
TAS        7050
AUSTRALIA
Ph  (03) 62 323 533
Fax (03) 62 323 351