/*******************************************************************************
 * Copyright (c) 2014-2015 IBM Corporation.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    IBM Zurich Research Lab - initial API, implementation and documentation
 *******************************************************************************/

#include "lmic.h"
#include <Arduino.h>

// ---------------------------------------- 
// Registers Mapping
#define RegFifo                                    0x00 // common
#define RegOpMode                                  0x01 // common
#define FSKRegBitrateMsb                           0x02
#define FSKRegBitrateLsb                           0x03
#define FSKRegFdevMsb                              0x04
#define FSKRegFdevLsb                              0x05
#define RegFrfMsb                                  0x06 // common
#define RegFrfMid                                  0x07 // common
#define RegFrfLsb                                  0x08 // common
#define RegPaConfig                                0x09 // common
#define RegPaRamp                                  0x0A // common
#define RegOcp                                     0x0B // common
#define RegLna                                     0x0C // common
#define FSKRegRxConfig                             0x0D
#define LORARegFifoAddrPtr                         0x0D
#define FSKRegRssiConfig                           0x0E
#define LORARegFifoTxBaseAddr                      0x0E
#define FSKRegRssiCollision                        0x0F
#define LORARegFifoRxBaseAddr                      0x0F 
#define FSKRegRssiThresh                           0x10
#define LORARegFifoRxCurrentAddr                   0x10
#define FSKRegRssiValue                            0x11
#define LORARegIrqFlagsMask                        0x11 
#define FSKRegRxBw                                 0x12
#define LORARegIrqFlags                            0x12 
#define FSKRegAfcBw                                0x13
#define LORARegRxNbBytes                           0x13 
#define FSKRegOokPeak                              0x14
#define LORARegRxHeaderCntValueMsb                 0x14 
#define FSKRegOokFix                               0x15
#define LORARegRxHeaderCntValueLsb                 0x15 
#define FSKRegOokAvg                               0x16
#define LORARegRxPacketCntValueMsb                 0x16 
#define LORARegRxpacketCntValueLsb                 0x17 
#define LORARegModemStat                           0x18 
#define LORARegPktSnrValue                         0x19 
#define FSKRegAfcFei                               0x1A
#define LORARegPktRssiValue                        0x1A 
#define FSKRegAfcMsb                               0x1B
#define LORARegRssiValue                           0x1B 
#define FSKRegAfcLsb                               0x1C
#define LORARegHopChannel                          0x1C 
#define FSKRegFeiMsb                               0x1D
#define LORARegModemConfig1                        0x1D 
#define FSKRegFeiLsb                               0x1E
#define LORARegModemConfig2                        0x1E 
#define FSKRegPreambleDetect                       0x1F
#define LORARegSymbTimeoutLsb                      0x1F 
#define FSKRegRxTimeout1                           0x20
#define LORARegPreambleMsb                         0x20 
#define FSKRegRxTimeout2                           0x21
#define LORARegPreambleLsb                         0x21 
#define FSKRegRxTimeout3                           0x22
#define LORARegPayloadLength                       0x22 
#define FSKRegRxDelay                              0x23
#define LORARegPayloadMaxLength                    0x23 
#define FSKRegOsc                                  0x24
#define LORARegHopPeriod                           0x24 
#define FSKRegPreambleMsb                          0x25
#define LORARegFifoRxByteAddr                      0x25
#define LORARegModemConfig3                        0x26
#define FSKRegPreambleLsb                          0x26
#define FSKRegSyncConfig                           0x27
#define LORARegFeiMsb                              0x28
#define FSKRegSyncValue1                           0x28
#define LORAFeiMib                                 0x29
#define FSKRegSyncValue2                           0x29
#define LORARegFeiLsb                              0x2A
#define FSKRegSyncValue3                           0x2A
#define FSKRegSyncValue4                           0x2B
#define LORARegRssiWideband                        0x2C
#define FSKRegSyncValue5                           0x2C
#define FSKRegSyncValue6                           0x2D
#define FSKRegSyncValue7                           0x2E
#define FSKRegSyncValue8                           0x2F
#define FSKRegPacketConfig1                        0x30
#define FSKRegPacketConfig2                        0x31
#define LORARegDetectOptimize                      0x31
#define FSKRegPayloadLength                        0x32
#define FSKRegNodeAdrs                             0x33
#define LORARegInvertIQ                            0x33
#define FSKRegBroadcastAdrs                        0x34
#define FSKRegFifoThresh                           0x35
#define FSKRegSeqConfig1                           0x36
#define FSKRegSeqConfig2                           0x37
#define LORARegDetectionThreshold                  0x37
#define FSKRegTimerResol                           0x38
#define FSKRegTimer1Coef                           0x39
#define LORARegSyncWord                            0x39
#define FSKRegTimer2Coef                           0x3A
#define FSKRegImageCal                             0x3B
#define FSKRegTemp                                 0x3C
#define FSKRegLowBat                               0x3D
#define FSKRegIrqFlags1                            0x3E
#define FSKRegIrqFlags2                            0x3F
#define RegDioMapping1                             0x40 // common
#define RegDioMapping2                             0x41 // common
#define RegVersion                                 0x42 // common
// #define RegAgcRef                                  0x43 // common
// #define RegAgcThresh1                              0x44 // common
// #define RegAgcThresh2                              0x45 // common
// #define RegAgcThresh3                              0x46 // common
// #define RegPllHop                                  0x4B // common
// #define RegTcxo                                    0x58 // common
#define RegPaDac                                   0x5A // common
// #define RegPll                                     0x5C // common
// #define RegPllLowPn                                0x5E // common
// #define RegFormerTemp                              0x6C // common
// #define RegBitRateFrac                             0x70 // common

// ----------------------------------------
// spread factors and mode for RegModemConfig2
#define SX1272_MC2_FSK  0x00
#define SX1272_MC2_SF7  0x70
#define SX1272_MC2_SF8  0x80
#define SX1272_MC2_SF9  0x90
#define SX1272_MC2_SF10 0xA0
#define SX1272_MC2_SF11 0xB0
#define SX1272_MC2_SF12 0xC0
// bandwidth for RegModemConfig1
#define SX1272_MC1_BW_125  0x00
#define SX1272_MC1_BW_250  0x40
#define SX1272_MC1_BW_500  0x80
// coding rate for RegModemConfig1
#define SX1272_MC1_CR_4_5 0x08
#define SX1272_MC1_CR_4_6 0x10
#define SX1272_MC1_CR_4_7 0x18
#define SX1272_MC1_CR_4_8 0x20
#define SX1272_MC1_IMPLICIT_HEADER_MODE_ON 0x04 // required for receive
#define SX1272_MC1_RX_PAYLOAD_CRCON        0x02
#define SX1272_MC1_LOW_DATA_RATE_OPTIMIZE  0x01 // mandated for SF11 and SF12
// transmit power configuration for RegPaConfig
#define SX1272_PAC_PA_SELECT_PA_BOOST 0x80
#define SX1272_PAC_PA_SELECT_RFIO_PIN 0x00


// sx1276 RegModemConfig1
#define SX1276_MC1_BW_125                0x70
#define SX1276_MC1_BW_250                0x80
#define SX1276_MC1_BW_500                0x90
#define SX1276_MC1_CR_4_5            0x02
#define SX1276_MC1_CR_4_6            0x04
#define SX1276_MC1_CR_4_7            0x06
#define SX1276_MC1_CR_4_8            0x08

#define SX1276_MC1_IMPLICIT_HEADER_MODE_ON    0x01 
                                                    
// sx1276 RegModemConfig2          
#define SX1276_MC2_RX_PAYLOAD_CRCON        0x04

// sx1276 RegModemConfig3          
#define SX1276_MC3_LOW_DATA_RATE_OPTIMIZE  0x08
#define SX1276_MC3_AGCAUTO                 0x04

// preamble for lora networks (nibbles swapped)
#define LORA_MAC_PREAMBLE                  0x34

#define RXLORA_RXMODE_RSSI_REG_MODEM_CONFIG1 0x0A
#ifdef CFG_sx1276_radio
#define RXLORA_RXMODE_RSSI_REG_MODEM_CONFIG2 0x70
#elif CFG_sx1272_radio
#define RXLORA_RXMODE_RSSI_REG_MODEM_CONFIG2 0x74
#endif



// ---------------------------------------- 
// Constants for radio registers
#define OPMODE_LORA      0x80
#define OPMODE_MASK      0x07
#define OPMODE_SLEEP     0x00
#define OPMODE_STANDBY   0x01
#define OPMODE_FSTX      0x02
#define OPMODE_TX        0x03
#define OPMODE_FSRX      0x04
#define OPMODE_RX        0x05
#define OPMODE_RX_SINGLE 0x06 
#define OPMODE_CAD       0x07 

// ----------------------------------------
// Bits masking the corresponding IRQs from the radio
#define IRQ_LORA_RXTOUT_MASK 0x80
#define IRQ_LORA_RXDONE_MASK 0x40
#define IRQ_LORA_CRCERR_MASK 0x20
#define IRQ_LORA_HEADER_MASK 0x10
#define IRQ_LORA_TXDONE_MASK 0x08
#define IRQ_LORA_CDDONE_MASK 0x04
#define IRQ_LORA_FHSSCH_MASK 0x02
#define IRQ_LORA_CDDETD_MASK 0x01

#define IRQ_FSK1_MODEREADY_MASK         0x80
#define IRQ_FSK1_RXREADY_MASK           0x40
#define IRQ_FSK1_TXREADY_MASK           0x20
#define IRQ_FSK1_PLLLOCK_MASK           0x10
#define IRQ_FSK1_RSSI_MASK              0x08
#define IRQ_FSK1_TIMEOUT_MASK           0x04
#define IRQ_FSK1_PREAMBLEDETECT_MASK    0x02
#define IRQ_FSK1_SYNCADDRESSMATCH_MASK  0x01
#define IRQ_FSK2_FIFOFULL_MASK          0x80
#define IRQ_FSK2_FIFOEMPTY_MASK         0x40
#define IRQ_FSK2_FIFOLEVEL_MASK         0x20
#define IRQ_FSK2_FIFOOVERRUN_MASK       0x10
#define IRQ_FSK2_PACKETSENT_MASK        0x08
#define IRQ_FSK2_PAYLOADREADY_MASK      0x04
#define IRQ_FSK2_CRCOK_MASK             0x02
#define IRQ_FSK2_LOWBAT_MASK            0x01

// ----------------------------------------
// DIO function mappings                D0D1D2D3
#define MAP_DIO0_LORA_RXDONE   0x00  // 00------
#define MAP_DIO0_LORA_TXDONE   0x40  // 01------
#define MAP_DIO1_LORA_RXTOUT   0x00  // --00----
#define MAP_DIO1_LORA_NOP      0x30  // --11----
#define MAP_DIO2_LORA_NOP      0xC0  // ----11--

#define MAP_DIO0_FSK_READY     0x00  // 00------ (packet sent / payload ready)
#define MAP_DIO1_FSK_NOP       0x30  // --11----
#define MAP_DIO2_FSK_TXNOP     0x04  // ----01--
#define MAP_DIO2_FSK_TIMEOUT   0x08  // ----10--


// FSK IMAGECAL defines
#define RF_IMAGECAL_AUTOIMAGECAL_MASK               0x7F
#define RF_IMAGECAL_AUTOIMAGECAL_ON                 0x80
#define RF_IMAGECAL_AUTOIMAGECAL_OFF                0x00  // Default

#define RF_IMAGECAL_IMAGECAL_MASK                   0xBF
#define RF_IMAGECAL_IMAGECAL_START                  0x40

#define RF_IMAGECAL_IMAGECAL_RUNNING                0x20
#define RF_IMAGECAL_IMAGECAL_DONE                   0x00  // Default


// RADIO STATE
// (initialized by radio_init(), used by radio_rand1())
static u1_t randbuf[16];


#ifdef CFG_sx1276_radio
#define LNA_RX_GAIN (0x20|0x1)
#elif CFG_sx1272_radio
#define LNA_RX_GAIN (0x20|0x03)
#else
#error Missing CFG_sx1272_radio/CFG_sx1276_radio
#endif


static void writeReg (u1_t addr, u1_t data ) {
    hal_pin_nss(0);
    hal_spi(addr | 0x80);
    hal_spi(data);
    hal_pin_nss(1);
}

static u1_t readReg (u1_t addr) {
    hal_pin_nss(0);
    hal_spi(addr & 0x7F);
    u1_t val = hal_spi(0x00);
    hal_pin_nss(1);
    return val;
}

static void writeBuf (u1_t addr, xref2u1_t buf, u1_t len) {
    hal_pin_nss(0);
    hal_spi(addr | 0x80);
    for (u1_t i=0; i<len; i++) {
        hal_spi(buf[i]);
    }
    hal_pin_nss(1);
}

static void readBuf (u1_t addr, xref2u1_t buf, u1_t len) {
    hal_pin_nss(0);
    hal_spi(addr & 0x7F);
    for (u1_t i=0; i<len; i++) {
        buf[i] = hal_spi(0x00);
    }
    hal_pin_nss(1);
}

static void opmode (u1_t mode) {
    writeReg(RegOpMode, (readReg(RegOpMode) & ~OPMODE_MASK) | mode);
}

static void opmodeLora() {
    u1_t u = OPMODE_LORA;
#ifdef CFG_sx1276_radio
    u |= 0x8;   // TBD: sx1276 high freq
#endif
    writeReg(RegOpMode, u);
}

static void opmodeFSK() {
    u1_t u = 0;
#ifdef CFG_sx1276_radio
    u |= 0x8;   // TBD: sx1276 high freq
#endif
    writeReg(RegOpMode, u);
}

// configure LoRa modem (cfg1, cfg2)
static void configLoraModem () {
    sf_t sf = getSf(LMIC.rps);

#ifdef CFG_sx1276_radio
        u1_t mc1 = 0, mc2 = 0, mc3 = 0;

        switch (getBw(LMIC.rps)) {
        case BW125: mc1 |= SX1276_MC1_BW_125; break;
        case BW250: mc1 |= SX1276_MC1_BW_250; break;
        case BW500: mc1 |= SX1276_MC1_BW_500; break;
        default:
            ASSERT(0);
        }
        switch( getCr(LMIC.rps) ) {
        case CR_4_5: mc1 |= SX1276_MC1_CR_4_5; break;
        case CR_4_6: mc1 |= SX1276_MC1_CR_4_6; break;
        case CR_4_7: mc1 |= SX1276_MC1_CR_4_7; break;
        case CR_4_8: mc1 |= SX1276_MC1_CR_4_8; break;
        default:
            ASSERT(0);
        }

        if (getIh(LMIC.rps)) {
            mc1 |= SX1276_MC1_IMPLICIT_HEADER_MODE_ON;
            writeReg(LORARegPayloadLength, getIh(LMIC.rps)); // required length
        }
        // set ModemConfig1
        writeReg(LORARegModemConfig1, mc1);

        mc2 = (SX1272_MC2_SF7 + ((sf-1)<<4));
        if (getNocrc(LMIC.rps) == 0) {
            mc2 |= SX1276_MC2_RX_PAYLOAD_CRCON;
        }
        writeReg(LORARegModemConfig2, mc2);
        
        mc3 = SX1276_MC3_AGCAUTO;
        if ((sf == SF11 || sf == SF12) && getBw(LMIC.rps) == BW125) {
            mc3 |= SX1276_MC3_LOW_DATA_RATE_OPTIMIZE;
        }
        writeReg(LORARegModemConfig3, mc3);
#elif CFG_sx1272_radio
        u1_t mc1 = (getBw(LMIC.rps)<<6);

        switch( getCr(LMIC.rps) ) {
        case CR_4_5: mc1 |= SX1272_MC1_CR_4_5; break;
        case CR_4_6: mc1 |= SX1272_MC1_CR_4_6; break;
        case CR_4_7: mc1 |= SX1272_MC1_CR_4_7; break;
        case CR_4_8: mc1 |= SX1272_MC1_CR_4_8; break;
        }
        
        if ((sf == SF11 || sf == SF12) && getBw(LMIC.rps) == BW125) {
            mc1 |= SX1272_MC1_LOW_DATA_RATE_OPTIMIZE;
        }
        
        if (getNocrc(LMIC.rps) == 0) {
            mc1 |= SX1272_MC1_RX_PAYLOAD_CRCON;
        }
        
        if (getIh(LMIC.rps)) {
            mc1 |= SX1272_MC1_IMPLICIT_HEADER_MODE_ON;
            writeReg(LORARegPayloadLength, getIh(LMIC.rps)); // required length
        }
        // set ModemConfig1
        writeReg(LORARegModemConfig1, mc1);
        
        // set ModemConfig2 (sf, AgcAutoOn=1 SymbTimeoutHi=00)
        writeReg(LORARegModemConfig2, (SX1272_MC2_SF7 + ((sf-1)<<4)) | 0x04);
#else
#error Missing CFG_sx1272_radio/CFG_sx1276_radio
#endif /* CFG_sx1272_radio */
}

static void configChannel () {
    // set frequency: FQ = (FRF * 32 Mhz) / (2 ^ 19)
    u64_t frf = ((u64_t)LMIC.freq << 19) / 32000000;
    writeReg(RegFrfMsb, (u1_t)(frf>>16));
    writeReg(RegFrfMid, (u1_t)(frf>> 8));
    writeReg(RegFrfLsb, (u1_t)(frf>> 0));
}



static void configPower () {
#ifdef CFG_sx1276_radio
    // no boost used for now
    s1_t pw = (s1_t)LMIC.txpow;
    if(pw >= 17) {
        pw = 15;
    } else if(pw < 2) {
        pw = 2;
    }
    // check board type for BOOST pin
    writeReg(RegPaConfig, (u1_t)(0x80|(pw&0xf)));
    writeReg(RegPaDac, readReg(RegPaDac)|0x4);

#elif CFG_sx1272_radio
    // set PA config (2-17 dBm using PA_BOOST)
    s1_t pw = (s1_t)LMIC.txpow;
    if(pw > 17) {
        pw = 17;
    } else if(pw < 2) {
        pw = 2;
    }
    writeReg(RegPaConfig, (u1_t)(0x80|(pw-2)));
#else
#error Missing CFG_sx1272_radio/CFG_sx1276_radio
#endif /* CFG_sx1272_radio */
}

static void txfsk () {
    // select FSK modem (from sleep mode)
    writeReg(RegOpMode, 0x10); // FSK, BT=0.5
    ASSERT(readReg(RegOpMode) == 0x10);
    // enter standby mode (required for FIFO loading))
    opmode(OPMODE_STANDBY);
    // set bitrate
    writeReg(FSKRegBitrateMsb, 0x02); // 50kbps
    writeReg(FSKRegBitrateLsb, 0x80);
    // set frequency deviation
    writeReg(FSKRegFdevMsb, 0x01); // +/- 25kHz
    writeReg(FSKRegFdevLsb, 0x99);
    // frame and packet handler settings
    writeReg(FSKRegPreambleMsb, 0x00);
    writeReg(FSKRegPreambleLsb, 0x05);
    writeReg(FSKRegSyncConfig, 0x12);
    writeReg(FSKRegPacketConfig1, 0xD0);
    writeReg(FSKRegPacketConfig2, 0x40);
    writeReg(FSKRegSyncValue1, 0xC1);
    writeReg(FSKRegSyncValue2, 0x94);
    writeReg(FSKRegSyncValue3, 0xC1);
    // configure frequency
    configChannel();
    // configure output power
    configPower();

    // set the IRQ mapping DIO0=PacketSent DIO1=NOP DIO2=NOP
    writeReg(RegDioMapping1, MAP_DIO0_FSK_READY|MAP_DIO1_FSK_NOP|MAP_DIO2_FSK_TXNOP);

    // initialize the payload size and address pointers    
    writeReg(FSKRegPayloadLength, LMIC.dataLen+1); // (insert length byte into payload))

    // download length byte and buffer to the radio FIFO
    writeReg(RegFifo, LMIC.dataLen);
    writeBuf(RegFifo, LMIC.frame, LMIC.dataLen);

    // enable antenna switch for TX
    hal_pin_rxtx(1);
    
    // now we actually start the transmission
    opmode(OPMODE_TX);
}

static void txlora () {
    // select LoRa modem (from sleep mode)
    //writeReg(RegOpMode, OPMODE_LORA);
    opmodeLora();
    ASSERT((readReg(RegOpMode) & OPMODE_LORA) != 0);

    // enter standby mode (required for FIFO loading))
    opmode(OPMODE_STANDBY);
    // configure LoRa modem (cfg1, cfg2)
    configLoraModem();
    // configure frequency
    configChannel();
    // configure output power
    writeReg(RegPaRamp, (readReg(RegPaRamp) & 0xF0) | 0x08); // set PA ramp-up time 50 uSec
    configPower();
    // set sync word
    writeReg(LORARegSyncWord, LORA_MAC_PREAMBLE);
    
    // set the IRQ mapping DIO0=TxDone DIO1=NOP DIO2=NOP
    writeReg(RegDioMapping1, MAP_DIO0_LORA_TXDONE|MAP_DIO1_LORA_NOP|MAP_DIO2_LORA_NOP);
    // clear all radio IRQ flags
    writeReg(LORARegIrqFlags, 0xFF);
    // mask all IRQs but TxDone
    writeReg(LORARegIrqFlagsMask, ~IRQ_LORA_TXDONE_MASK);

    // initialize the payload size and address pointers    
    writeReg(LORARegFifoTxBaseAddr, 0x00);
    writeReg(LORARegFifoAddrPtr, 0x00);
    writeReg(LORARegPayloadLength, LMIC.dataLen);
       
    // download buffer to the radio FIFO
    writeBuf(RegFifo, LMIC.frame, LMIC.dataLen);

    // enable antenna switch for TX
    hal_pin_rxtx(1);
    
    // now we actually start the transmission
    opmode(OPMODE_TX);
}

// start transmitter (buf=LMIC.frame, len=LMIC.dataLen)
static void starttx () {
    ASSERT( (readReg(RegOpMode) & OPMODE_MASK) == OPMODE_SLEEP );
    if(getSf(LMIC.rps) == FSK) { // FSK modem
        txfsk();
    } else { // LoRa modem
        txlora();
    }
    // the radio will go back to STANDBY mode as soon as the TX is finished
    // the corresponding IRQ will inform us about completion.
}

enum { RXMODE_SINGLE, RXMODE_SCAN, RXMODE_RSSI };

static const u1_t rxlorairqmask[] = {
    [RXMODE_SINGLE] = IRQ_LORA_RXDONE_MASK|IRQ_LORA_RXTOUT_MASK,
    [RXMODE_SCAN]   = IRQ_LORA_RXDONE_MASK,
    [RXMODE_RSSI]   = 0x00,
};

// start LoRa receiver (time=LMIC.rxtime, timeout=LMIC.rxsyms, result=LMIC.frame[LMIC.dataLen])
static void rxlora (u1_t rxmode) {
    // select LoRa modem (from sleep mode)
    opmodeLora();
    ASSERT((readReg(RegOpMode) & OPMODE_LORA) != 0);
    // enter standby mode (warm up))
    opmode(OPMODE_STANDBY);
    // don't use MAC settings at startup
    if(rxmode == RXMODE_RSSI) { // use fixed settings for rssi scan
        writeReg(LORARegModemConfig1, RXLORA_RXMODE_RSSI_REG_MODEM_CONFIG1);
        writeReg(LORARegModemConfig2, RXLORA_RXMODE_RSSI_REG_MODEM_CONFIG2);
    } else { // single or continuous rx mode
        // configure LoRa modem (cfg1, cfg2)
        configLoraModem();
        // configure frequency
        configChannel();
    }
    // set LNA gain
    writeReg(RegLna, LNA_RX_GAIN); 
    // set max payload size
    writeReg(LORARegPayloadMaxLength, 255);
    // use inverted I/Q signal (prevent mote-to-mote communication)
    writeReg(LORARegInvertIQ, readReg(LORARegInvertIQ)|(1<<6));
    // set symbol timeout (for single rx)
    writeReg(LORARegSymbTimeoutLsb, LMIC.rxsyms);
    // set sync word
    writeReg(LORARegSyncWord, LORA_MAC_PREAMBLE);
    
    // configure DIO mapping DIO0=RxDone DIO1=RxTout DIO2=NOP
    writeReg(RegDioMapping1, MAP_DIO0_LORA_RXDONE|MAP_DIO1_LORA_RXTOUT|MAP_DIO2_LORA_NOP);
    // clear all radio IRQ flags
    writeReg(LORARegIrqFlags, 0xFF);
    // enable required radio IRQs
    writeReg(LORARegIrqFlagsMask, ~rxlorairqmask[rxmode]);

    // enable antenna switch for RX
    hal_pin_rxtx(0);

    // now instruct the radio to receive
    if (rxmode == RXMODE_SINGLE) { // single rx
        hal_waitUntil(LMIC.rxtime); // busy wait until exact rx time
        opmode(OPMODE_RX_SINGLE);
    } else { // continous rx (scan or rssi)
        opmode(OPMODE_RX); 
    }
}

static void rxfsk (u1_t rxmode) {
    // only single rx (no continuous scanning, no noise sampling)
    ASSERT( rxmode == RXMODE_SINGLE );
    // select FSK modem (from sleep mode)
    //writeReg(RegOpMode, 0x00); // (not LoRa)
    opmodeFSK();
    ASSERT((readReg(RegOpMode) & OPMODE_LORA) == 0);
    // enter standby mode (warm up))
    opmode(OPMODE_STANDBY);
    // configure frequency
    configChannel();
    // set LNA gain
    //writeReg(RegLna, 0x20|0x03); // max gain, boost enable
    writeReg(RegLna, LNA_RX_GAIN);
    // configure receiver
    writeReg(FSKRegRxConfig, 0x1E); // AFC auto, AGC, trigger on preamble?!?
    // set receiver bandwidth
    writeReg(FSKRegRxBw, 0x0B); // 50kHz SSb
    // set AFC bandwidth
    writeReg(FSKRegAfcBw, 0x12); // 83.3kHz SSB
    // set preamble detection
    writeReg(FSKRegPreambleDetect, 0xAA); // enable, 2 bytes, 10 chip errors
    // set sync config
    writeReg(FSKRegSyncConfig, 0x12); // no auto restart, preamble 0xAA, enable, fill FIFO, 3 bytes sync
    // set packet config
    writeReg(FSKRegPacketConfig1, 0xD8); // var-length, whitening, crc, no auto-clear, no adr filter
    writeReg(FSKRegPacketConfig2, 0x40); // packet mode
    // set sync value
    writeReg(FSKRegSyncValue1, 0xC1);
    writeReg(FSKRegSyncValue2, 0x94);
    writeReg(FSKRegSyncValue3, 0xC1);
    // set preamble timeout
    writeReg(FSKRegRxTimeout2, 0xFF);//(LMIC.rxsyms+1)/2);
    // set bitrate
    writeReg(FSKRegBitrateMsb, 0x02); // 50kbps
    writeReg(FSKRegBitrateLsb, 0x80);
    // set frequency deviation
    writeReg(FSKRegFdevMsb, 0x01); // +/- 25kHz
    writeReg(FSKRegFdevLsb, 0x99);
    
    // configure DIO mapping DIO0=PayloadReady DIO1=NOP DIO2=TimeOut
    writeReg(RegDioMapping1, MAP_DIO0_FSK_READY|MAP_DIO1_FSK_NOP|MAP_DIO2_FSK_TIMEOUT);

    // enable antenna switch for RX
    hal_pin_rxtx(0);
    
    // now instruct the radio to receive
    hal_waitUntil(LMIC.rxtime); // busy wait until exact rx time
    opmode(OPMODE_RX); // no single rx mode available in FSK
}

static void startrx (u1_t rxmode) {
    ASSERT( (readReg(RegOpMode) & OPMODE_MASK) == OPMODE_SLEEP );
    if(getSf(LMIC.rps) == FSK) { // FSK modem
        rxfsk(rxmode);
    } else { // LoRa modem
        rxlora(rxmode);
    }
    // the radio will go back to STANDBY mode as soon as the RX is finished
    // or timed out, and the corresponding IRQ will inform us about completion.
}

// get random seed from wideband noise rssi
void radio_init () {
    hal_disableIRQs();

    // manually reset radio
#ifdef CFG_sx1276_radio
    hal_pin_rst(0); // drive RST pin low
#else
    hal_pin_rst(1); // drive RST pin high
#endif
    hal_waitUntil(os_getTime()+ms2osticks(1)); // wait >100us
    hal_pin_rst(2); // configure RST pin floating!
    hal_waitUntil(os_getTime()+ms2osticks(5)); // wait 5ms

    opmode(OPMODE_SLEEP);

    // some sanity checks, e.g., read version number
    u1_t v = readReg(RegVersion);

    Serial.println(v);

#ifdef CFG_sx1276_radio
    ASSERT(v == 0x12 ); 
#elif CFG_sx1272_radio
    ASSERT(v == 0x22);
#else
#error Missing CFG_sx1272_radio/CFG_sx1276_radio
#endif
    // seed 15-byte randomness via noise rssi
    rxlora(RXMODE_RSSI);
    while( (readReg(RegOpMode) & OPMODE_MASK) != OPMODE_RX ); // continuous rx
    for(int i=1; i<16; i++) {
        for(int j=0; j<8; j++) {
            u1_t b; // wait for two non-identical subsequent least-significant bits
            while( (b = readReg(LORARegRssiWideband) & 0x01) == (readReg(LORARegRssiWideband) & 0x01) );
            randbuf[i] = (randbuf[i] << 1) | b;
        }
    }
    randbuf[0] = 16; // set initial index
  
#ifdef CFG_sx1276mb1_board
    // chain calibration
    writeReg(RegPaConfig, 0);
    
    // Launch Rx chain calibration for LF band
    writeReg(FSKRegImageCal, (readReg(FSKRegImageCal) & RF_IMAGECAL_IMAGECAL_MASK)|RF_IMAGECAL_IMAGECAL_START);
    while((readReg(FSKRegImageCal)&RF_IMAGECAL_IMAGECAL_RUNNING) == RF_IMAGECAL_IMAGECAL_RUNNING){ ; }

    // Sets a Frequency in HF band
    u4_t frf = 868000000;
    writeReg(RegFrfMsb, (u1_t)(frf>>16));
    writeReg(RegFrfMid, (u1_t)(frf>> 8));
    writeReg(RegFrfLsb, (u1_t)(frf>> 0));

    // Launch Rx chain calibration for HF band 
    writeReg(FSKRegImageCal, (readReg(FSKRegImageCal) & RF_IMAGECAL_IMAGECAL_MASK)|RF_IMAGECAL_IMAGECAL_START);
    while((readReg(FSKRegImageCal) & RF_IMAGECAL_IMAGECAL_RUNNING) == RF_IMAGECAL_IMAGECAL_RUNNING) { ; }
#endif /* CFG_sx1276mb1_board */

    opmode(OPMODE_SLEEP);

    hal_enableIRQs();
}

// return next random byte derived from seed buffer
// (buf[0] holds index of next byte to be returned)
u1_t radio_rand1 () {
    u1_t i = randbuf[0];
    ASSERT( i != 0 );
    if( i==16 ) {
        os_aes(AES_ENC, randbuf, 16); // encrypt seed with any key
        i = 0;
    }
    u1_t v = randbuf[i++];
    randbuf[0] = i;
    return v;
}

u1_t radio_rssi () {
    hal_disableIRQs();
    u1_t r = readReg(LORARegRssiValue);
    hal_enableIRQs();
    return r;
}

static const u2_t LORA_RXDONE_FIXUP[] = {
    [FSK]  =     us2osticks(0), // (   0 ticks)
    [SF7]  =     us2osticks(0), // (   0 ticks)
    [SF8]  =  us2osticks(1648), // (  54 ticks)
    [SF9]  =  us2osticks(3265), // ( 107 ticks)
    [SF10] =  us2osticks(7049), // ( 231 ticks)
    [SF11] = us2osticks(13641), // ( 447 ticks)
    [SF12] = us2osticks(31189), // (1022 ticks)
};

// called by hal ext IRQ handler
// (radio goes to stanby mode after tx/rx operations)
void radio_irq_handler (u1_t dio) {
    ostime_t now = os_getTime();
    if( (readReg(RegOpMode) & OPMODE_LORA) != 0) { // LORA modem
        u1_t flags = readReg(LORARegIrqFlags);
        if( flags & IRQ_LORA_TXDONE_MASK ) {
            // save exact tx time
            LMIC.txend = now - us2osticks(43); // TXDONE FIXUP
        } else if( flags & IRQ_LORA_RXDONE_MASK ) {
            // save exact rx time
            if(getBw(LMIC.rps) == BW125) {
                now -= LORA_RXDONE_FIXUP[getSf(LMIC.rps)];
            }
            LMIC.rxtime = now;
            // read the PDU and inform the MAC that we received something
            LMIC.dataLen = (readReg(LORARegModemConfig1) & SX1272_MC1_IMPLICIT_HEADER_MODE_ON) ?
                readReg(LORARegPayloadLength) : readReg(LORARegRxNbBytes);
            // set FIFO read address pointer
            writeReg(LORARegFifoAddrPtr, readReg(LORARegFifoRxCurrentAddr)); 
            // now read the FIFO
            readBuf(RegFifo, LMIC.frame, LMIC.dataLen);
            // read rx quality parameters
            LMIC.snr  = readReg(LORARegPktSnrValue); // SNR [dB] * 4
            LMIC.rssi = readReg(LORARegPktRssiValue) - 125 + 64; // RSSI [dBm] (-196...+63)
        } else if( flags & IRQ_LORA_RXTOUT_MASK ) {
            // indicate timeout
            LMIC.dataLen = 0;
        }
        // mask all radio IRQs
        writeReg(LORARegIrqFlagsMask, 0xFF);
        // clear radio IRQ flags
        writeReg(LORARegIrqFlags, 0xFF);
    } else { // FSK modem
        u1_t flags1 = readReg(FSKRegIrqFlags1);
        u1_t flags2 = readReg(FSKRegIrqFlags2);
        if( flags2 & IRQ_FSK2_PACKETSENT_MASK ) {
            // save exact tx time
            LMIC.txend = now;
        } else if( flags2 & IRQ_FSK2_PAYLOADREADY_MASK ) {
            // save exact rx time
            LMIC.rxtime = now;
            // read the PDU and inform the MAC that we received something
            LMIC.dataLen = readReg(FSKRegPayloadLength);
            // now read the FIFO
            readBuf(RegFifo, LMIC.frame, LMIC.dataLen);
            // read rx quality parameters
            LMIC.snr  = 0; // determine snr
            LMIC.rssi = 0; // determine rssi
        } else if( flags1 & IRQ_FSK1_TIMEOUT_MASK ) {
            // indicate timeout
            LMIC.dataLen = 0;
        } else {
            //while(1);
            // Do not infinite loop when interrupt triggers unexpectedly
            // Instead, call ASSERT, which calls hal_failed, so there is at least a
            // traceable error. (MK)
            ASSERT(0);
        }
    }
    // go from stanby to sleep
    opmode(OPMODE_SLEEP);
    // run os job (use preset func ptr)
    os_setCallback(&LMIC.osjob, LMIC.osjob.func);
}

void os_radio (u1_t mode) {
    hal_disableIRQs();
    switch (mode) {
      case RADIO_RST:
        // put radio to sleep
        opmode(OPMODE_SLEEP);
        break;

      case RADIO_TX:
        // transmit frame now
        starttx(); // buf=LMIC.frame, len=LMIC.dataLen
        break;
      
      case RADIO_RX:
        // receive frame now (exactly at rxtime)
        startrx(RXMODE_SINGLE); // buf=LMIC.frame, time=LMIC.rxtime, timeout=LMIC.rxsyms
        break;

      case RADIO_RXON:
        // start scanning for beacon now
        startrx(RXMODE_SCAN); // buf=LMIC.frame
        break;
    }
    hal_enableIRQs();
}
