xyFC/src/rx.c

/*
 * FrSky RX 2-way protocol
 */

#include <stdint.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/eeprom.h>
#include <avr/wdt.h>

#include "cc2500.h"
#include "cppm.h"
#include "spi.h"
#include "timer.h"
#include "rx.h"

#define CHANNELS 8
#define PPM_MIN 1000
#define PPM_MAX 2000
#define HOP_DATA_LENGTH 60
#define EEPROM_BASE_ADDRESS 100
#define MISSING_PACKET_DELAY 9
#define SEEK_CHANNEL_SKIP   13
#define MAX_MISSING_PACKET 20
#define FAILSAFE_MISSING_PACKET 170
#define RSSI_OVER_PPM 7
#define RSSI_OFFSET 71
#define RSSI_MIN -103
#define RSSI_MAX -96
#define PPM_SCALE 0.67

uint8_t ccData[27];
uint8_t ccLen;
uint8_t packet = 0;
uint8_t channr = 0;
uint8_t missingPackets = 0;
uint8_t hopData[HOP_DATA_LENGTH];
uint8_t listLength;
uint8_t txid[2];
uint8_t counter = 0;
uint8_t failed = 0;
uint8_t frequencyOffsetHack = 0;
uint16_t c[8];
int rssi;

static uint16_t ppmBuffer[CHANNELS];

static long map(long x, long in_min, long in_max, long out_min, long out_max);
static long constrain(long x, long min, long max);

static void initialize(uint8_t bind);
static void binding(void);
static void tuning(void);
static void performBind(void);
static void nextChannel(uint8_t skip);
static void readBindingData(void);
static void writeBindingData(void);

void rxInit(void) {
    initialize(1); // binding
    binding();

    initialize(0); // data
    cc2500WriteReg(CC2500_0A_CHANNR, hopData[channr]);//0A-hop
    cc2500WriteReg(CC2500_23_FSCAL3, 0x89); //23-89
    cc2500Strobe(CC2500_SRX);
}

static void initialize(uint8_t bind) {
    cc2500ResetChip();
    cc2500WriteReg(CC2500_02_IOCFG0,   0x01); // RX complete interrupt(GDO0)
    cc2500WriteReg(CC2500_17_MCSM1,    0x0C);
    cc2500WriteReg(CC2500_18_MCSM0,    0x18);
    cc2500WriteReg(CC2500_06_PKTLEN,   0x19); // Leave room for appended status bytes
    cc2500WriteReg(CC2500_08_PKTCTRL0, 0x05);
    cc2500WriteReg(CC2500_3E_PATABLE,  0xFF);
    cc2500WriteReg(CC2500_0B_FSCTRL1,  0x08);
    cc2500WriteReg(CC2500_0C_FSCTRL0,  0x00);
    cc2500WriteReg(CC2500_0D_FREQ2,    0x5C);
    cc2500WriteReg(CC2500_0E_FREQ1,    0x76);
    cc2500WriteReg(CC2500_0F_FREQ0,    0x27);
    cc2500WriteReg(CC2500_10_MDMCFG4,  0xAA);
    cc2500WriteReg(CC2500_11_MDMCFG3,  0x39);
    cc2500WriteReg(CC2500_12_MDMCFG2,  0x11);
    cc2500WriteReg(CC2500_13_MDMCFG1,  0x23);
    cc2500WriteReg(CC2500_14_MDMCFG0,  0x7A);
    cc2500WriteReg(CC2500_15_DEVIATN,  0x42);
    cc2500WriteReg(CC2500_19_FOCCFG,   0x16);
    cc2500WriteReg(CC2500_1A_BSCFG,    0x6C);
    cc2500WriteReg(CC2500_1B_AGCCTRL2, 0x03);
    cc2500WriteReg(CC2500_1C_AGCCTRL1, 0x40);
    cc2500WriteReg(CC2500_1D_AGCCTRL0, 0x91);
    cc2500WriteReg(CC2500_21_FREND1,   0x56);
    cc2500WriteReg(CC2500_22_FREND0,   0x10);
    cc2500WriteReg(CC2500_23_FSCAL3,   0xA9);
    cc2500WriteReg(CC2500_24_FSCAL2,   0x05);
    cc2500WriteReg(CC2500_25_FSCAL1,   0x00);
    cc2500WriteReg(CC2500_26_FSCAL0,   0x11);
    cc2500WriteReg(CC2500_29_FSTEST,   0x59);
    cc2500WriteReg(CC2500_2C_TEST2,    0x88);
    cc2500WriteReg(CC2500_2D_TEST1,    0x31);
    cc2500WriteReg(CC2500_2E_TEST0,    0x0B);
    cc2500WriteReg(CC2500_03_FIFOTHR,  0x0F);

    cc2500WriteReg(CC2500_09_ADDR, bind ? 0x03 : txid[0]);

    cc2500Strobe(CC2500_SIDLE); // Go to idle...

    // hack: Append status, filter by address, auto-flush on bad crc, PQT=0
    cc2500WriteReg(CC2500_07_PKTCTRL1, 0x0D);

    //cc2500WriteReg(CC2500_0C_FSCTRL0, 0); // Frequency offset
    cc2500WriteReg(CC2500_0C_FSCTRL0, bind ? 0x00 : frequencyOffsetHack);

    cc2500WriteReg(CC2500_0A_CHANNR, 0x00);
}

static void binding(void) {
    readBindingData();
    if ((txid[0] != 0xff) || (txid[1] != 0xff)) {
        // valid binding data found
        return;
    }

    // No valid txid, forcing bind
    tuning();

    //frequencyOffsetHack = 0xC8; // for test
    cc2500WriteReg(CC2500_0C_FSCTRL0, frequencyOffsetHack);
    eeprom_write_byte(EEPROM_BASE_ADDRESS + 101, frequencyOffsetHack);

    performBind();
}

static void tuning() {
    cc2500Strobe(CC2500_SRX); // enter in rx mode

    int frequencyOffsetTimer = 0;
    while (1) {
        frequencyOffsetTimer++;
        if (frequencyOffsetTimer > 3000) {
            frequencyOffsetTimer = 0;
            cc2500WriteReg(CC2500_0C_FSCTRL0, frequencyOffsetHack);
            frequencyOffsetHack += 10;
            if (frequencyOffsetHack > 250) {
                frequencyOffsetHack = 0;
            }
            //cc2500Strobe(CC2500_SRX); // enter in rx mode
        }

        if (GDO_1) {
            ccLen = cc2500ReadReg(CC2500_3B_RXBYTES | CC2500_READ_BURST) & 0x7F;
            if (ccLen) {
                cc2500ReadFifo(ccData, ccLen);
                if ((ccData[ccLen - 1] & 0x80)
                        && (ccData[2] == 0x01)
                        && (ccData[5] == 0x00)) {
                    break;
                }
            }
        }

        wdt_reset();
    }
}

static void performBind(void) {
    cc2500Strobe(CC2500_SRX); // enter in rx mode

    while (1) {
        if (GDO_1) {
            ccLen = cc2500ReadReg(CC2500_3B_RXBYTES | CC2500_READ_BURST) & 0x7F;
            if (ccLen) {
                cc2500ReadFifo(ccData, ccLen);
                if ((ccData[ccLen - 1] & 0x80)
                        && (ccData[2] == 0x01)
                        && (ccData[5] == 0x00)) {
                    txid[0] = ccData[3];
                    txid[1] = ccData[4];
                    for (uint8_t n = 0; n < 5; n++) {
                        hopData[ccData[5] + n] = ccData[6 + n];
                    }
                    break;
                }
            }
        }

        wdt_reset();
    }

    listLength = 0;
    uint8_t eol = 0;
    for (uint8_t bindIdx = 0x05; bindIdx <= 120; bindIdx += 5) {
        while (1) {
            if (GDO_1) {
                ccLen = cc2500ReadReg(CC2500_3B_RXBYTES | CC2500_READ_BURST) & 0x7F;
                if (ccLen) {
                    cc2500ReadFifo(ccData, ccLen);
                    if ((ccData[ccLen - 1] & 0x80)
                            && (ccData[2] == 0x01)
                            && (ccData[3] == txid[0])
                            && (ccData[4] == txid[1])
                            && (ccData[5] == bindIdx)) {
                        for (uint8_t n = 0; n < 5; n++) {
                            //if (ccData[6 + n] == ccData[ccLen - 3]) {
                              if (ccData[6 + n] <= 3) {
                                eol = 1;
                                listLength = ccData[5] + n;
                                break;
                            }
                            hopData[ccData[5] + n] = ccData[6 + n];
                        }
                        break;
                    }
                }
            }

            wdt_reset();
        }

        if (eol) {
            break; // End of list found, stop!
        }
    }

    writeBindingData();
    cc2500Strobe(CC2500_SIDLE); // Back to idle
}

static void nextChannel(uint8_t skip) {
    channr += skip;
    if (channr >= listLength) {
        channr -= listLength;
    }

    cc2500WriteReg(CC2500_0A_CHANNR, hopData[channr]);
    cc2500WriteReg(CC2500_23_FSCAL3, 0x89);
}

static void readBindingData() {
    for (uint8_t i = 0; i < 2; i++) {
        txid[i] = eeprom_read_byte(EEPROM_BASE_ADDRESS + i);
    }

    for (uint8_t i = 0; i < HOP_DATA_LENGTH; i++) {
        hopData[i] = eeprom_read_byte(EEPROM_BASE_ADDRESS + 10 + i);
    }

    listLength = eeprom_read_byte(EEPROM_BASE_ADDRESS + 100);
    frequencyOffsetHack = eeprom_read_byte(EEPROM_BASE_ADDRESS + 101);
}

static void writeBindingData() {
    for (uint8_t i = 0; i < 2; i++) {
        eeprom_write_byte(EEPROM_BASE_ADDRESS + i, txid[i]);
    }

    for (uint8_t i = 0; i < HOP_DATA_LENGTH; i++) {
        eeprom_write_byte(EEPROM_BASE_ADDRESS + 10 + i, hopData[i]);
    }

    eeprom_write_byte(EEPROM_BASE_ADDRESS + 100, listLength);
}

void rxReceivePacket() {
    time_t time = timerGet();

    if (missingPackets > FAILSAFE_MISSING_PACKET) {
        failed = 1;
        missingPackets = 0;
    }

    while (1) {
        if ((timerGet() - time) > MISSING_PACKET_DELAY) {
            missingPackets++;
            cc2500Strobe(CC2500_SIDLE);
            if (missingPackets > MAX_MISSING_PACKET) {
                nextChannel(SEEK_CHANNEL_SKIP);
                counter++;
                //if (counter > (MAX_MISSING_PACKET << 1)) LED_ON;
                if (counter == (MAX_MISSING_PACKET << 2)) counter = 0;
                break;
            } else
                nextChannel(1);
            break;
        }

        if (GDO_1) {
            ccLen = cc2500ReadReg(CC2500_3B_RXBYTES | CC2500_READ_BURST) & 0x7F;
            if (ccLen > 20) {
                ccLen = 20;
            }
            if (ccLen) {
                cc2500ReadFifo((uint8_t *)ccData, ccLen);
                if (ccData[ccLen - 1] & 0x80) { // Only if correct CRC
                    missingPackets = 0;
                    if ((ccData[0] == 0x11) // Correct length
                            && (ccData[1] == txid[0]) // Correct txid
                            && (ccData[2] == txid[1])) {
                        packet = 1;

#ifdef RSSI_OVER_PPM
                        int rssi_dec = cc2500ReadReg(CC2500_34_RSSI | CC2500_READ_BURST);
                        if (rssi_dec < 128) {
                            rssi = ((rssi_dec / 2) - RSSI_OFFSET) & 0x7f;
                        } else {
                            rssi = (((rssi_dec - 256) / 2)) - RSSI_OFFSET;
                        }
                        rssi = constrain(rssi, RSSI_MIN, RSSI_MAX);
#endif

                        cc2500Strobe(CC2500_SIDLE);
                        nextChannel(1);
                        failed = 0;
                        break;
                    }
                }
            }
        }

        wdt_reset();
    }

    if (packet != 0) {
        packet = 0;
        c[0] = (uint16_t)(ccData[10] & 0x0F) << 8 | ccData[6];
        c[1] = (uint16_t)(ccData[10] & 0xF0) << 4 | ccData[7];
        c[2] = (uint16_t)(ccData[11] & 0x0F) << 8 | ccData[8];
        c[3] = (uint16_t)(ccData[11] & 0xF0) << 4 | ccData[9];
        c[4] = (uint16_t)(ccData[16] & 0x0F) << 8 | ccData[12];
        c[5] = (uint16_t)(ccData[16] & 0xF0) << 4 | ccData[13];
        c[6] = (uint16_t)(ccData[17] & 0x0F) << 8 | ccData[14];
        c[7] = (uint16_t)(ccData[17] & 0xF0) << 4 | ccData[15];

        for (int i = 0; i < CHANNELS; i++) {
            ppmBuffer[i] = PPM_SCALE * c[i];
            if ((ppmBuffer[i] < 900) || (ppmBuffer[i] > 2100)) {
                ppmBuffer[i] = 850;
            }
        }

#ifdef RSSI_OVER_PPM
        ppmBuffer[RSSI_OVER_PPM] = map(rssi, RSSI_MIN, RSSI_MAX, PPM_MIN, PPM_MAX);
#endif

        cppmCopy(ppmBuffer);
    }

    cc2500Strobe(CC2500_SRX);
}

static long map(long x, long in_min, long in_max, long out_min, long out_max) {
    return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

static long constrain(long x, long min, long max) {
    if (x < min) {
        x = min;
    }
    if (x > max) {
        x = max;
    }
    return x;
}