ESP8266 HSPI interrupt handler for spying on a SPI bus

hspi_slave_isr_handler.cpp

const int length = 12;              // length of packet minus the first byte
uint8_t data[length];               // raw data received
volatile bool data_ready = false;   // set by HSPI interrupt handler when data is received

void ICACHE_RAM_ATTR hspi_slave_isr_handler(void *) {
    uint32_t istatus = SPIIR;
    if(istatus & (1 << SPII1)) {    //SPI1 ISR
        uint32_t status = SPI1S;
        SPI1S &= ~(0x3E0);          //disable interrupts
        SPI1S |= SPISSRES;          //reset
        SPI1S &= ~(0x1F);           //clear interrupts
        SPI1S |= (0x3E0);           //enable interrupts

        if(status & SPISWBIS) {
            uint8_t *p = data;
            for(int i = 0; i < length / 4; i++) {
                uint32_t dword = SPI1W(i);
                *p++ = dword;
                *p++ = dword >> 8;
                *p++ = dword >> 16;
                *p++ = dword >> 24;
            }
            data_ready = true;
        }
    } else if(istatus & (1 << SPII0)) { //SPI0 ISR
        SPI0S &= ~(0x3ff);//clear SPI ISR
    } else if(istatus & (1 << SPII2)) {} //I2S ISR
}