Support for walkera telemetry.

static u16 devo_telemetry_cb()
{
    int delay;
    
    if (txState == 0) {
        DEVO_BuildPacket();
        CYRF_WriteDataPacket(packet);
        txState = 1;
        return 900;
    }
    if (txState == 1) {
        int i = 0;
        u8 reg;
        while (! ((reg = CYRF_ReadRegister(0x04)) & 0x02)) {
            if (++i >= NUM_WAIT_LOOPS)
                break;
        }
        if (((reg & 0x22) == 0x20) || (CYRF_ReadRegister(0x02) & 0x80)) {
            CYRF_Reset();
            cyrf_init();
            cyrf_set_bound_sop_code();
            CYRF_ConfigRFChannel(*radio_ch_ptr);
            //printf("Rst CYRF\n");
            delay = 1500;
            txState = 3;
        } else {
            if (state == DEVO_BOUND) {
                /* exit binding state */
                state = DEVO_BOUND_3;
                cyrf_set_bound_sop_code();
            }
            if(pkt_num == 0 || bind_counter > 0) {
                delay = 1500;
                txState = 3;
            } else {
                CYRF_SetTxRxMode(RX_EN); //Receive mode
                CYRF_WriteRegister(CYRF_05_RX_CTRL, 0x80); //Prepare to receive (do not enable any IRQ)
                txState = 2;
                return 1300;
            }
        }
    }
    if(txState == 2) {  // this won't be true in emulator so we need to simulate it somehow
        //Read telemetry if needed
        if(CYRF_ReadDataPacketLen(packet) == 16) {
            parse_telemetry_packet();
        }
        CYRF_SetTxRxMode(TX_EN); //Write mode
#ifdef EMULATOR
        u8 telem_bit = rand32() % 7; // random number in [0, 7)
        packet[0] =  TELEMETRY_ENABLE + telem_bit; // allow emulator to simulate telemetry parsing to prevent future bugs in the telemetry monitor
        //printf("telem 1st packet: 0x%x\n", packet[0]);
        for(int i = 1; i < 13; i++)
            packet[i] = rand32() % 256;
        parse_telemetry_packet();
        for(int i = 0; i < TELEM_UPDATE_SIZE; i++)
            Telemetry.updated[i] = 0xff;
#endif
        delay = 200;
        txState = 3;
    }
    if(txState == 3) {
        if(pkt_num == 0) {
            //Keep tx power updated
            CYRF_WriteRegister(CYRF_03_TX_CFG, 0x08 | Model.tx_power);
            radio_ch_ptr = radio_ch_ptr == &radio_ch[2] ? radio_ch : radio_ch_ptr + 1;
            CYRF_ConfigRFChannel(*radio_ch_ptr);
        }
        txState = 0;
    }
    return delay;
}