...
void init()
{
    SPI0CN    = 0x05;
    P0MDOUT   = 0x02;
    XBR0      = 0x02;
    XBR1      = 0xC0;
    OSCICN    = 0x81;
    IE        = 0xC0;
}

...

static void spi_isr(void) interrupt 6
{
    // doesn't come in here at all
    int q = 0;
    q++;
}

...