uc_stm32_can.cpp

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/*
 * Copyright (C) 2014 Pavel Kirienko <pavel.kirienko@gmail.com>
 */

#include <cassert>
#include <cstring>
#include <uavcan_stm32/can.hpp>
#include <uavcan_stm32/clock.hpp>
#include "internal.hpp"

#if UAVCAN_STM32_NUTTX
# include <nuttx/arch.h>
# include <nuttx/irq.h>
# include <arch/board/board.h>
#else
# error "Unknown OS"
#endif

#if UAVCAN_STM32_NUTTX
# if !defined(STM32_IRQ_CAN1TX) && !defined(STM32_IRQ_CAN1RX0)
#  define STM32_IRQ_CAN1TX      STM32_IRQ_USBHPCANTX
#  define STM32_IRQ_CAN1RX0     STM32_IRQ_USBLPCANRX0
# endif
extern "C"
{
    static int can1_irq(const int irq, void *, void *);
#if UAVCAN_STM32_NUM_IFACES > 1
    static int can2_irq(const int irq, void *, void *);
#endif
}
#endif

/* STM32F3's only CAN inteface does not have a number. */
#if defined(STM32F3XX)
#define RCC_APB1ENR_CAN1EN     RCC_APB1ENR_CANEN
#define RCC_APB1RSTR_CAN1RST   RCC_APB1RSTR_CANRST
#define CAN1_TX_IRQn           CAN_TX_IRQn
#define CAN1_RX0_IRQn          CAN_RX0_IRQn
#define CAN1_RX1_IRQn          CAN_RX1_IRQn
#endif


namespace uavcan_stm32
{
namespace
{

CanIface *ifaces[UAVCAN_STM32_NUM_IFACES] = {
    UAVCAN_NULLPTR
#if UAVCAN_STM32_NUM_IFACES > 1
    , UAVCAN_NULLPTR
#endif
};

inline void handleTxInterrupt(uavcan::uint8_t iface_index)
{
    UAVCAN_ASSERT(iface_index < UAVCAN_STM32_NUM_IFACES);
    uavcan::uint64_t utc_usec = clock::getUtcUSecFromCanInterrupt();

    if (utc_usec > 0) {
        utc_usec--;
    }

    if (ifaces[iface_index] != UAVCAN_NULLPTR) {
        ifaces[iface_index]->handleTxInterrupt(utc_usec);

    } else {
        UAVCAN_ASSERT(0);
    }
}

inline void handleRxInterrupt(uavcan::uint8_t iface_index, uavcan::uint8_t fifo_index)
{
    UAVCAN_ASSERT(iface_index < UAVCAN_STM32_NUM_IFACES);
    uavcan::uint64_t utc_usec = clock::getUtcUSecFromCanInterrupt();

    if (utc_usec > 0) {
        utc_usec--;
    }

    if (ifaces[iface_index] != UAVCAN_NULLPTR) {
        ifaces[iface_index]->handleRxInterrupt(fifo_index, utc_usec);

    } else {
        UAVCAN_ASSERT(0);
    }
}

} // namespace

/*
 * CanIface::RxQueue
 */
void CanIface::RxQueue::registerOverflow()
{
    if (overflow_cnt_ < 0xFFFFFFFF) {
        overflow_cnt_++;
    }
}

void CanIface::RxQueue::push(const uavcan::CanFrame &frame, const uint64_t &utc_usec, uavcan::CanIOFlags flags)
{
    buf_[in_].frame    = frame;
    buf_[in_].utc_usec = utc_usec;
    buf_[in_].flags    = flags;
    in_++;

    if (in_ >= capacity_) {
        in_ = 0;
    }

    len_++;

    if (len_ > capacity_) {
        len_ = capacity_;
        registerOverflow();
        out_++;

        if (out_ >= capacity_) {
            out_ = 0;
        }
    }
}

void CanIface::RxQueue::pop(uavcan::CanFrame &out_frame, uavcan::uint64_t &out_utc_usec, uavcan::CanIOFlags &out_flags)
{
    if (len_ > 0) {
        out_frame    = buf_[out_].frame;
        out_utc_usec = buf_[out_].utc_usec;
        out_flags    = buf_[out_].flags;
        out_++;

        if (out_ >= capacity_) {
            out_ = 0;
        }

        len_--;

    } else { UAVCAN_ASSERT(0); }
}

void CanIface::RxQueue::reset()
{
    in_ = 0;
    out_ = 0;
    len_ = 0;
    overflow_cnt_ = 0;
}

/*
 * CanIface
 */
const uavcan::uint32_t CanIface::TSR_ABRQx[CanIface::NumTxMailboxes] = {
    bxcan::TSR_ABRQ0,
    bxcan::TSR_ABRQ1,
    bxcan::TSR_ABRQ2
};

int CanIface::computeTimings(const uavcan::uint32_t target_bitrate, Timings &out_timings)
{
    if (target_bitrate < 1) {
        return -ErrInvalidBitRate;
    }

    /*
     * Hardware configuration
     */
#if UAVCAN_STM32_NUTTX
    const uavcan::uint32_t pclk = STM32_PCLK1_FREQUENCY;
#else
# error "Unknown OS"
#endif

    static const int MaxBS1 = 16;
    static const int MaxBS2 = 8;

    /*
     * Ref. "Automatic Baudrate Detection in CANopen Networks", U. Koppe, MicroControl GmbH & Co. KG
     *      CAN in Automation, 2003
     *
     * According to the source, optimal quanta per bit are:
     *   Bitrate        Optimal Maximum
     *   1000 kbps      8       10
     *   500  kbps      16      17
     *   250  kbps      16      17
     *   125  kbps      16      17
     */
    const int max_quanta_per_bit = (target_bitrate >= 1000000) ? 10 : 17;

    UAVCAN_ASSERT(max_quanta_per_bit <= (MaxBS1 + MaxBS2));

    static const int MaxSamplePointLocation = 900;

    /*
     * Computing (prescaler * BS):
     *   BITRATE = 1 / (PRESCALER * (1 / PCLK) * (1 + BS1 + BS2))       -- See the Reference Manual
     *   BITRATE = PCLK / (PRESCALER * (1 + BS1 + BS2))                 -- Simplified
     * let:
     *   BS = 1 + BS1 + BS2                                             -- Number of time quanta per bit
     *   PRESCALER_BS = PRESCALER * BS
     * ==>
     *   PRESCALER_BS = PCLK / BITRATE
     */
    const uavcan::uint32_t prescaler_bs = pclk / target_bitrate;

    /*
     * Searching for such prescaler value so that the number of quanta per bit is highest.
     */
    uavcan::uint8_t bs1_bs2_sum = uavcan::uint8_t(max_quanta_per_bit - 1);

    while ((prescaler_bs % (1 + bs1_bs2_sum)) != 0) {
        if (bs1_bs2_sum <= 2) {
            return -ErrInvalidBitRate;          // No solution
        }

        bs1_bs2_sum--;
    }

    const uavcan::uint32_t prescaler = prescaler_bs / (1 + bs1_bs2_sum);

    if ((prescaler < 1U) || (prescaler > 1024U)) {
        return -ErrInvalidBitRate;              // No solution
    }

    /*
     * Now we have a constraint: (BS1 + BS2) == bs1_bs2_sum.
     * We need to find the values so that the sample point is as close as possible to the optimal value.
     *
     *   Solve[(1 + bs1)/(1 + bs1 + bs2) == 7/8, bs2]  (* Where 7/8 is 0.875, the recommended sample point location *)
     *   {{bs2 -> (1 + bs1)/7}}
     *
     * Hence:
     *   bs2 = (1 + bs1) / 7
     *   bs1 = (7 * bs1_bs2_sum - 1) / 8
     *
     * Sample point location can be computed as follows:
     *   Sample point location = (1 + bs1) / (1 + bs1 + bs2)
     *
     * Since the optimal solution is so close to the maximum, we prepare two solutions, and then pick the best one:
     *   - With rounding to nearest
     *   - With rounding to zero
     */
    struct BsPair {
        uavcan::uint8_t bs1;
        uavcan::uint8_t bs2;
        uavcan::uint16_t sample_point_permill;

        BsPair() :
            bs1(0),
            bs2(0),
            sample_point_permill(0)
        { }

        BsPair(uavcan::uint8_t bs1_bs2_sum, uavcan::uint8_t arg_bs1) :
            bs1(arg_bs1),
            bs2(uavcan::uint8_t(bs1_bs2_sum - bs1)),
            sample_point_permill(uavcan::uint16_t(1000 * (1 + bs1) / (1 + bs1 + bs2)))
        {
            UAVCAN_ASSERT(bs1_bs2_sum > arg_bs1);
        }

        bool isValid() const { return (bs1 >= 1) && (bs1 <= MaxBS1) && (bs2 >= 1) && (bs2 <= MaxBS2); }
    };

    // First attempt with rounding to nearest
    BsPair solution(bs1_bs2_sum, uavcan::uint8_t(((7 * bs1_bs2_sum - 1) + 4) / 8));

    if (solution.sample_point_permill > MaxSamplePointLocation) {
        // Second attempt with rounding to zero
        solution = BsPair(bs1_bs2_sum, uavcan::uint8_t((7 * bs1_bs2_sum - 1) / 8));
    }

    /*
     * Final validation
     * Helpful Python:
     * def sample_point_from_btr(x):
     *     assert 0b0011110010000000111111000000000 & x == 0
     *     ts2,ts1,brp = (x>>20)&7, (x>>16)&15, x&511
     *     return (1+ts1+1)/(1+ts1+1+ts2+1)
     *
     */
    if ((target_bitrate != (pclk / (prescaler * (1 + solution.bs1 + solution.bs2)))) || !solution.isValid()) {
        UAVCAN_ASSERT(0);
        return -ErrLogic;
    }

    UAVCAN_STM32_LOG("Timings: quanta/bit: %d, sample point location: %.1f%%",
             int(1 + solution.bs1 + solution.bs2), float(solution.sample_point_permill) / 10.F);

    out_timings.prescaler = uavcan::uint16_t(prescaler - 1U);
    out_timings.sjw = 0;                                        // Which means one
    out_timings.bs1 = uavcan::uint8_t(solution.bs1 - 1);
    out_timings.bs2 = uavcan::uint8_t(solution.bs2 - 1);
    return 0;
}

uavcan::int16_t CanIface::send(const uavcan::CanFrame &frame, uavcan::MonotonicTime tx_deadline,
                   uavcan::CanIOFlags flags)
{
    if (frame.isErrorFrame() || frame.dlc > 8) {
        return -ErrUnsupportedFrame;
    }

    /*
     * Normally we should perform the same check as in @ref canAcceptNewTxFrame(), because
     * it is possible that the highest-priority frame between select() and send() could have been
     * replaced with a lower priority one due to TX timeout. But we don't do this check because:
     *
     *  - It is a highly unlikely scenario.
     *
     *  - Frames do not timeout on a properly functioning bus. Since frames do not timeout, the new
     *    frame can only have higher priority, which doesn't break the logic.
     *
     *  - If high-priority frames are timing out in the TX queue, there's probably a lot of other
     *    issues to take care of before this one becomes relevant.
     *
     *  - It takes CPU time. Not just CPU time, but critical section time, which is expensive.
     */
    CriticalSectionLocker lock;

    /*
     * Seeking for an empty slot
     */
    uavcan::uint8_t txmailbox = 0xFF;

    if ((can_->TSR & bxcan::TSR_TME0) == bxcan::TSR_TME0) {
        txmailbox = 0;

    } else if ((can_->TSR & bxcan::TSR_TME1) == bxcan::TSR_TME1) {
        txmailbox = 1;

    } else if ((can_->TSR & bxcan::TSR_TME2) == bxcan::TSR_TME2) {
        txmailbox = 2;

    } else {
        return 0;       // No transmission for you.
    }

    peak_tx_mailbox_index_ = uavcan::max(peak_tx_mailbox_index_, txmailbox);    // Statistics

    /*
     * Setting up the mailbox
     */
    bxcan::TxMailboxType &mb = can_->TxMailbox[txmailbox];

    if (frame.isExtended()) {
        mb.TIR = ((frame.id & uavcan::CanFrame::MaskExtID) << 3) | bxcan::TIR_IDE;

    } else {
        mb.TIR = ((frame.id & uavcan::CanFrame::MaskStdID) << 21);
    }

    if (frame.isRemoteTransmissionRequest()) {
        mb.TIR |= bxcan::TIR_RTR;
    }

    mb.TDTR = frame.dlc;

    mb.TDHR = (uavcan::uint32_t(frame.data[7]) << 24) |
          (uavcan::uint32_t(frame.data[6]) << 16) |
          (uavcan::uint32_t(frame.data[5]) << 8)  |
          (uavcan::uint32_t(frame.data[4]) << 0);
    mb.TDLR = (uavcan::uint32_t(frame.data[3]) << 24) |
          (uavcan::uint32_t(frame.data[2]) << 16) |
          (uavcan::uint32_t(frame.data[1]) << 8)  |
          (uavcan::uint32_t(frame.data[0]) << 0);

    mb.TIR |= bxcan::TIR_TXRQ;  // Go.

    /*
     * Registering the pending transmission so we can track its deadline and loopback it as needed
     */
    TxItem &txi = pending_tx_[txmailbox];
    txi.deadline       = tx_deadline;
    txi.frame          = frame;
    txi.loopback       = (flags & uavcan::CanIOFlagLoopback) != 0;
    txi.abort_on_error = (flags & uavcan::CanIOFlagAbortOnError) != 0;
    txi.pending        = true;
    return 1;
}

uavcan::int16_t CanIface::receive(uavcan::CanFrame &out_frame, uavcan::MonotonicTime &out_ts_monotonic,
                  uavcan::UtcTime &out_ts_utc, uavcan::CanIOFlags &out_flags)
{
    out_ts_monotonic = clock::getMonotonic();  // High precision is not required for monotonic timestamps
    uavcan::uint64_t utc_usec = 0;
    {
        CriticalSectionLocker lock;

        if (rx_queue_.getLength() == 0) {
            return 0;
        }

        rx_queue_.pop(out_frame, utc_usec, out_flags);
    }
    out_ts_utc = uavcan::UtcTime::fromUSec(utc_usec);
    return 1;
}

uavcan::int16_t CanIface::configureFilters(const uavcan::CanFilterConfig *filter_configs,
        uavcan::uint16_t num_configs)
{
    if (num_configs <= NumFilters) {
        CriticalSectionLocker lock;

        can_->FMR |= bxcan::FMR_FINIT;

        // Slave (CAN2) gets half of the filters
        can_->FMR &= ~0x00003F00UL;
        can_->FMR |= static_cast<uint32_t>(NumFilters) << 8;

        can_->FFA1R = 0x0AAAAAAA; // FIFO's are interleaved between filters
        can_->FM1R = 0; // Identifier Mask mode
        can_->FS1R = 0x7ffffff; // Single 32-bit for all

        const uint8_t filter_start_index = (self_index_ == 0) ? 0 : NumFilters;

        if (num_configs == 0) {
            can_->FilterRegister[filter_start_index].FR1 = 0;
            can_->FilterRegister[filter_start_index].FR2 = 0;
            // We can't directly overwrite FA1R because that breaks the other CAN interface
            can_->FA1R |= 1U << filter_start_index;              // Other filters may still be enabled, we don't care

        } else {
            for (uint8_t i = 0; i < NumFilters; i++) {
                if (i < num_configs) {
                    uint32_t id   = 0;
                    uint32_t mask = 0;

                    const uavcan::CanFilterConfig *const cfg = filter_configs + i;

                    if ((cfg->id & uavcan::CanFrame::FlagEFF) || !(cfg->mask & uavcan::CanFrame::FlagEFF)) {
                        id   = (cfg->id   & uavcan::CanFrame::MaskExtID) << 3;
                        mask = (cfg->mask & uavcan::CanFrame::MaskExtID) << 3;
                        id |= bxcan::RIR_IDE;

                    } else {
                        id   = (cfg->id   & uavcan::CanFrame::MaskStdID) << 21;  // Regular std frames, nothing fancy.
                        mask = (cfg->mask & uavcan::CanFrame::MaskStdID) << 21;  // Boring.
                    }

                    if (cfg->id & uavcan::CanFrame::FlagRTR) {
                        id |= bxcan::RIR_RTR;
                    }

                    if (cfg->mask & uavcan::CanFrame::FlagEFF) {
                        mask |= bxcan::RIR_IDE;
                    }

                    if (cfg->mask & uavcan::CanFrame::FlagRTR) {
                        mask |= bxcan::RIR_RTR;
                    }

                    can_->FilterRegister[filter_start_index + i].FR1 = id;
                    can_->FilterRegister[filter_start_index + i].FR2 = mask;

                    can_->FA1R |= (1 << (filter_start_index + i));

                } else {
                    can_->FA1R &= ~(1 << (filter_start_index + i));
                }
            }
        }

        can_->FMR &= ~bxcan::FMR_FINIT;

        return 0;
    }

    return -ErrFilterNumConfigs;
}

bool CanIface::waitMsrINakBitStateChange(bool target_state)
{
#if UAVCAN_STM32_NUTTX
    const unsigned Timeout = 1000;
#else
    const unsigned Timeout = 2000000;
#endif

    for (unsigned wait_ack = 0; wait_ack < Timeout; wait_ack++) {
        const bool state = (can_->MSR & bxcan::MSR_INAK) != 0;

        if (state == target_state) {
            return true;
        }

#if UAVCAN_STM32_NUTTX
        ::usleep(1000);
#endif
    }

    return false;
}

int CanIface::init(const uavcan::uint32_t bitrate, const OperatingMode mode)
{
    /*
     * We need to silence the controller in the first order, otherwise it may interfere with the following operations.
     */
    {
        CriticalSectionLocker lock;

        can_->MCR &= ~bxcan::MCR_SLEEP; // Exit sleep mode
        can_->MCR |= bxcan::MCR_INRQ;   // Request init

        can_->IER = 0;                  // Disable interrupts while initialization is in progress
    }

    if (!waitMsrINakBitStateChange(true)) {
        UAVCAN_STM32_LOG("MSR INAK not set");
        can_->MCR = bxcan::MCR_RESET;
        return -ErrMsrInakNotSet;
    }

    /*
     * Object state - interrupts are disabled, so it's safe to modify it now
     */
    rx_queue_.reset();
    error_cnt_ = 0;
    served_aborts_cnt_ = 0;
    uavcan::fill_n(pending_tx_, NumTxMailboxes, TxItem());
    peak_tx_mailbox_index_ = 0;
    had_activity_ = false;

    /*
     * CAN timings for this bitrate
     */
    Timings timings;
    const int timings_res = computeTimings(bitrate, timings);

    if (timings_res < 0) {
        can_->MCR = bxcan::MCR_RESET;
        return timings_res;
    }

    UAVCAN_STM32_LOG("Timings: presc=%u sjw=%u bs1=%u bs2=%u",
             unsigned(timings.prescaler), unsigned(timings.sjw), unsigned(timings.bs1), unsigned(timings.bs2));

    /*
     * Hardware initialization (the hardware has already confirmed initialization mode, see above)
     */
    can_->MCR = bxcan::MCR_ABOM | bxcan::MCR_AWUM | bxcan::MCR_INRQ;  // RM page 648

    can_->BTR = ((timings.sjw & 3U)  << 24) |
            ((timings.bs1 & 15U) << 16) |
            ((timings.bs2 & 7U)  << 20) |
            (timings.prescaler & 1023U) |
            ((mode == SilentMode) ? bxcan::BTR_SILM : 0);

    can_->IER = bxcan::IER_TMEIE |   // TX mailbox empty
            bxcan::IER_FMPIE0 |  // RX FIFO 0 is not empty
            bxcan::IER_FMPIE1;   // RX FIFO 1 is not empty

    can_->MCR &= ~bxcan::MCR_INRQ;   // Leave init mode

    if (!waitMsrINakBitStateChange(false)) {
        UAVCAN_STM32_LOG("MSR INAK not cleared");
        can_->MCR = bxcan::MCR_RESET;
        return -ErrMsrInakNotCleared;
    }

    /*
     * Default filter configuration
     */
    if (self_index_ == 0) {
        can_->FMR |= bxcan::FMR_FINIT;

        can_->FMR &= 0xFFFFC0F1;
        can_->FMR |= static_cast<uavcan::uint32_t>(NumFilters) << 8;  // Slave (CAN2) gets half of the filters

        can_->FFA1R = 0;                           // All assigned to FIFO0 by default
        can_->FM1R = 0;                            // Indentifier Mask mode

#if UAVCAN_STM32_NUM_IFACES > 1
        can_->FS1R = 0x7ffffff;                    // Single 32-bit for all
        can_->FilterRegister[0].FR1 = 0;          // CAN1 accepts everything
        can_->FilterRegister[0].FR2 = 0;
        can_->FilterRegister[NumFilters].FR1 = 0; // CAN2 accepts everything
        can_->FilterRegister[NumFilters].FR2 = 0;
        can_->FA1R = 1 | (1 << NumFilters);        // One filter per each iface
#else
        can_->FS1R = 0x1fff;
        can_->FilterRegister[0].FR1 = 0;
        can_->FilterRegister[0].FR2 = 0;
        can_->FA1R = 1;
#endif

        can_->FMR &= ~bxcan::FMR_FINIT;
    }

    return 0;
}

void CanIface::handleTxMailboxInterrupt(uavcan::uint8_t mailbox_index, bool txok, const uavcan::uint64_t utc_usec)
{
    UAVCAN_ASSERT(mailbox_index < NumTxMailboxes);

    had_activity_ = had_activity_ || txok;

    TxItem &txi = pending_tx_[mailbox_index];

    if (txi.loopback && txok && txi.pending) {
        rx_queue_.push(txi.frame, utc_usec, uavcan::CanIOFlagLoopback);
    }

    txi.pending = false;
}

void CanIface::handleTxInterrupt(const uavcan::uint64_t utc_usec)
{
    // TXOK == false means that there was a hardware failure
    if (can_->TSR & bxcan::TSR_RQCP0) {
        const bool txok = can_->TSR & bxcan::TSR_TXOK0;
        can_->TSR = bxcan::TSR_RQCP0;
        handleTxMailboxInterrupt(0, txok, utc_usec);
    }

    if (can_->TSR & bxcan::TSR_RQCP1) {
        const bool txok = can_->TSR & bxcan::TSR_TXOK1;
        can_->TSR = bxcan::TSR_RQCP1;
        handleTxMailboxInterrupt(1, txok, utc_usec);
    }

    if (can_->TSR & bxcan::TSR_RQCP2) {
        const bool txok = can_->TSR & bxcan::TSR_TXOK2;
        can_->TSR = bxcan::TSR_RQCP2;
        handleTxMailboxInterrupt(2, txok, utc_usec);
    }

    update_event_.signalFromInterrupt();

    pollErrorFlagsFromISR();

}

void CanIface::handleRxInterrupt(uavcan::uint8_t fifo_index, uavcan::uint64_t utc_usec)
{
    UAVCAN_ASSERT(fifo_index < 2);

    volatile uavcan::uint32_t *const rfr_reg = (fifo_index == 0) ? &can_->RF0R : &can_->RF1R;

    if ((*rfr_reg & bxcan::RFR_FMP_MASK) == 0) {
        UAVCAN_ASSERT(0);  // Weird, IRQ is here but no data to read
        return;
    }

    /*
     * Register overflow as a hardware error
     */
    if ((*rfr_reg & bxcan::RFR_FOVR) != 0) {
        error_cnt_++;
    }

    /*
     * Read the frame contents
     */
    uavcan::CanFrame frame;
    const bxcan::RxMailboxType &rf = can_->RxMailbox[fifo_index];

    if ((rf.RIR & bxcan::RIR_IDE) == 0) {
        frame.id = uavcan::CanFrame::MaskStdID & (rf.RIR >> 21);

    } else {
        frame.id = uavcan::CanFrame::MaskExtID & (rf.RIR >> 3);
        frame.id |= uavcan::CanFrame::FlagEFF;
    }

    if ((rf.RIR & bxcan::RIR_RTR) != 0) {
        frame.id |= uavcan::CanFrame::FlagRTR;
    }

    frame.dlc = rf.RDTR & 15;

    frame.data[0] = uavcan::uint8_t(0xFF & (rf.RDLR >> 0));
    frame.data[1] = uavcan::uint8_t(0xFF & (rf.RDLR >> 8));
    frame.data[2] = uavcan::uint8_t(0xFF & (rf.RDLR >> 16));
    frame.data[3] = uavcan::uint8_t(0xFF & (rf.RDLR >> 24));
    frame.data[4] = uavcan::uint8_t(0xFF & (rf.RDHR >> 0));
    frame.data[5] = uavcan::uint8_t(0xFF & (rf.RDHR >> 8));
    frame.data[6] = uavcan::uint8_t(0xFF & (rf.RDHR >> 16));
    frame.data[7] = uavcan::uint8_t(0xFF & (rf.RDHR >> 24));

    *rfr_reg = bxcan::RFR_RFOM | bxcan::RFR_FOVR | bxcan::RFR_FULL;  // Release FIFO entry we just read

    /*
     * Store with timeout into the FIFO buffer and signal update event
     */
    rx_queue_.push(frame, utc_usec, 0);
    had_activity_ = true;
    update_event_.signalFromInterrupt();

    pollErrorFlagsFromISR();

}

void CanIface::pollErrorFlagsFromISR()
{
    const uavcan::uint8_t lec = uavcan::uint8_t((can_->ESR & bxcan::ESR_LEC_MASK) >> bxcan::ESR_LEC_SHIFT);

    if (lec != 0) {
        can_->ESR = 0;
        error_cnt_++;

        // Serving abort requests
        for (int i = 0; i < NumTxMailboxes; i++) {  // Dear compiler, may I suggest you to unroll this loop please.
            TxItem &txi = pending_tx_[i];

            if (txi.pending && txi.abort_on_error) {
                can_->TSR = TSR_ABRQx[i];
                txi.pending = false;
                served_aborts_cnt_++;
            }
        }
    }
}

void CanIface::discardTimedOutTxMailboxes(uavcan::MonotonicTime current_time)
{
    CriticalSectionLocker lock;

    for (int i = 0; i < NumTxMailboxes; i++) {
        TxItem &txi = pending_tx_[i];

        if (txi.pending && txi.deadline < current_time) {
            can_->TSR = TSR_ABRQx[i];  // Goodnight sweet transmission
            txi.pending = false;
            error_cnt_++;
        }
    }
}

bool CanIface::canAcceptNewTxFrame(const uavcan::CanFrame &frame) const
{
    /*
     * We can accept more frames only if the following conditions are satisfied:
     *  - There is at least one TX mailbox free (obvious enough);
     *  - The priority of the new frame is higher than priority of all TX mailboxes.
     */
    {
        static const uavcan::uint32_t TME = bxcan::TSR_TME0 | bxcan::TSR_TME1 | bxcan::TSR_TME2;
        const uavcan::uint32_t tme = can_->TSR & TME;

        if (tme == TME) {   // All TX mailboxes are free (as in freedom).
            return true;
        }

        if (tme == 0) {     // All TX mailboxes are busy transmitting.
            return false;
        }
    }

    /*
     * The second condition requires a critical section.
     */
    CriticalSectionLocker lock;

    for (int mbx = 0; mbx < NumTxMailboxes; mbx++) {
        if (pending_tx_[mbx].pending && !frame.priorityHigherThan(pending_tx_[mbx].frame)) {
            return false;       // There's a mailbox whose priority is higher or equal the priority of the new frame.
        }
    }

    return true;                // This new frame will be added to a free TX mailbox in the next @ref send().
}

bool CanIface::isRxBufferEmpty() const
{
    CriticalSectionLocker lock;
    return rx_queue_.getLength() == 0;
}

uavcan::uint64_t CanIface::getErrorCount() const
{
    CriticalSectionLocker lock;
    return error_cnt_ + rx_queue_.getOverflowCount();
}

unsigned CanIface::getRxQueueLength() const
{
    CriticalSectionLocker lock;
    return rx_queue_.getLength();
}

bool CanIface::hadActivity()
{
    CriticalSectionLocker lock;
    const bool ret = had_activity_;
    had_activity_ = false;
    return ret;
}

/*
 * CanDriver
 */
uavcan::CanSelectMasks CanDriver::makeSelectMasks(const uavcan::CanFrame * (& pending_tx)[uavcan::MaxCanIfaces]) const
{
    uavcan::CanSelectMasks msk;

    // Iface 0
    msk.read  = if0_.isRxBufferEmpty() ? 0 : 1;

    if (pending_tx[0] != UAVCAN_NULLPTR) {
        msk.write = if0_.canAcceptNewTxFrame(*pending_tx[0]) ? 1 : 0;
    }

    // Iface 1
#if UAVCAN_STM32_NUM_IFACES > 1

    if (!if1_.isRxBufferEmpty()) {
        msk.read |= 1 << 1;
    }

    if (pending_tx[1] != UAVCAN_NULLPTR) {
        if (if1_.canAcceptNewTxFrame(*pending_tx[1])) {
            msk.write |= 1 << 1;
        }
    }

#endif
    return msk;
}

bool CanDriver::hasReadableInterfaces() const
{
#if UAVCAN_STM32_NUM_IFACES == 1
    return !if0_.isRxBufferEmpty();
#elif UAVCAN_STM32_NUM_IFACES == 2
    return !if0_.isRxBufferEmpty() || !if1_.isRxBufferEmpty();
#else
# error UAVCAN_STM32_NUM_IFACES
#endif
}

uavcan::int16_t CanDriver::select(uavcan::CanSelectMasks &inout_masks,
                  const uavcan::CanFrame * (& pending_tx)[uavcan::MaxCanIfaces],
                  const uavcan::MonotonicTime blocking_deadline)
{
    const uavcan::CanSelectMasks in_masks = inout_masks;
    const uavcan::MonotonicTime time = clock::getMonotonic();

    if0_.discardTimedOutTxMailboxes(time);              // Check TX timeouts - this may release some TX slots
    {
        CriticalSectionLocker cs_locker;
        if0_.pollErrorFlagsFromISR();
    }

#if UAVCAN_STM32_NUM_IFACES > 1
    if1_.discardTimedOutTxMailboxes(time);
    {
        CriticalSectionLocker cs_locker;
        if1_.pollErrorFlagsFromISR();
    }
#endif

    inout_masks = makeSelectMasks(pending_tx);          // Check if we already have some of the requested events

    if ((inout_masks.read  & in_masks.read)  != 0 ||
        (inout_masks.write & in_masks.write) != 0) {
        return 1;
    }

    (void)update_event_.wait(blocking_deadline - time); // Block until timeout expires or any iface updates
    inout_masks = makeSelectMasks(pending_tx);  // Return what we got even if none of the requested events are set
    return 1;                                   // Return value doesn't matter as long as it is non-negative
}


void CanDriver::initOnce()
{
    /*
     * CAN1, CAN2
     */
    {
        CriticalSectionLocker lock;
#if UAVCAN_STM32_NUTTX
        modifyreg32(STM32_RCC_APB1ENR,  0, RCC_APB1ENR_CAN1EN);
        modifyreg32(STM32_RCC_APB1RSTR, 0, RCC_APB1RSTR_CAN1RST);
        modifyreg32(STM32_RCC_APB1RSTR, RCC_APB1RSTR_CAN1RST, 0);
# if UAVCAN_STM32_NUM_IFACES > 1
        modifyreg32(STM32_RCC_APB1ENR,  0, RCC_APB1ENR_CAN2EN);
        modifyreg32(STM32_RCC_APB1RSTR, 0, RCC_APB1RSTR_CAN2RST);
        modifyreg32(STM32_RCC_APB1RSTR, RCC_APB1RSTR_CAN2RST, 0);
# endif
#else
        RCC->APB1ENR  |=  RCC_APB1ENR_CAN1EN;
        RCC->APB1RSTR |=  RCC_APB1RSTR_CAN1RST;
        RCC->APB1RSTR &= ~RCC_APB1RSTR_CAN1RST;
# if UAVCAN_STM32_NUM_IFACES > 1
        RCC->APB1ENR  |=  RCC_APB1ENR_CAN2EN;
        RCC->APB1RSTR |=  RCC_APB1RSTR_CAN2RST;
        RCC->APB1RSTR &= ~RCC_APB1RSTR_CAN2RST;
# endif
#endif
    }

    /*
     * IRQ
     */
#if UAVCAN_STM32_NUTTX
# define IRQ_ATTACH(irq, handler)                          \
    {                                                      \
        const int res = irq_attach(irq, handler, NULL);    \
        (void)res;                                         \
        assert(res >= 0);                                  \
        up_enable_irq(irq);                                \
    }
    IRQ_ATTACH(STM32_IRQ_CAN1TX,  can1_irq);
    IRQ_ATTACH(STM32_IRQ_CAN1RX0, can1_irq);
    IRQ_ATTACH(STM32_IRQ_CAN1RX1, can1_irq);
# if UAVCAN_STM32_NUM_IFACES > 1
    IRQ_ATTACH(STM32_IRQ_CAN2TX,  can2_irq);
    IRQ_ATTACH(STM32_IRQ_CAN2RX0, can2_irq);
    IRQ_ATTACH(STM32_IRQ_CAN2RX1, can2_irq);
# endif
# undef IRQ_ATTACH
#endif
}

int CanDriver::init(const uavcan::uint32_t bitrate, const CanIface::OperatingMode mode)
{
    int res = 0;

    UAVCAN_STM32_LOG("Bitrate %lu mode %d", static_cast<unsigned long>(bitrate), static_cast<int>(mode));

    static bool initialized_once = false;

    if (!initialized_once) {
        initialized_once = true;
        UAVCAN_STM32_LOG("First initialization");
        initOnce();
    }

    /*
     * CAN1
     */
    UAVCAN_STM32_LOG("Initing iface 0...");
    ifaces[0] = &if0_;                          // This link must be initialized first,
    res = if0_.init(bitrate, mode);             // otherwise an IRQ may fire while the interface is not linked yet;

    if (res < 0) {                              // a typical race condition.
        UAVCAN_STM32_LOG("Iface 0 init failed %i", res);
        ifaces[0] = UAVCAN_NULLPTR;
        goto fail;
    }

    /*
     * CAN2
     */
#if UAVCAN_STM32_NUM_IFACES > 1
    UAVCAN_STM32_LOG("Initing iface 1...");
    ifaces[1] = &if1_;                          // Same thing here.
    res = if1_.init(bitrate, mode);

    if (res < 0) {
        UAVCAN_STM32_LOG("Iface 1 init failed %i", res);
        ifaces[1] = UAVCAN_NULLPTR;
        goto fail;
    }

#endif

    UAVCAN_STM32_LOG("CAN drv init OK");
    UAVCAN_ASSERT(res >= 0);
    return res;

fail:
    UAVCAN_STM32_LOG("CAN drv init failed %i", res);
    UAVCAN_ASSERT(res < 0);
    return res;
}

CanIface *CanDriver::getIface(uavcan::uint8_t iface_index)
{
    if (iface_index < UAVCAN_STM32_NUM_IFACES) {
        return ifaces[iface_index];
    }

    return UAVCAN_NULLPTR;
}

bool CanDriver::hadActivity()
{
    bool ret = if0_.hadActivity();
#if UAVCAN_STM32_NUM_IFACES > 1
    ret |= if1_.hadActivity();
#endif
    return ret;
}

} // namespace uavcan_stm32

/*
 * Interrupt handlers
 */
extern "C"
{

#if UAVCAN_STM32_NUTTX

    static int can1_irq(const int irq, void *, void *)
    {
        if (irq == STM32_IRQ_CAN1TX) {
            uavcan_stm32::handleTxInterrupt(0);

        } else if (irq == STM32_IRQ_CAN1RX0) {
            uavcan_stm32::handleRxInterrupt(0, 0);

        } else if (irq == STM32_IRQ_CAN1RX1) {
            uavcan_stm32::handleRxInterrupt(0, 1);

        } else {
            PANIC();
        }

        return 0;
    }

# if UAVCAN_STM32_NUM_IFACES > 1

    static int can2_irq(const int irq, void *, void *)
    {
        if (irq == STM32_IRQ_CAN2TX) {
            uavcan_stm32::handleTxInterrupt(1);

        } else if (irq == STM32_IRQ_CAN2RX0) {
            uavcan_stm32::handleRxInterrupt(1, 0);

        } else if (irq == STM32_IRQ_CAN2RX1) {
            uavcan_stm32::handleRxInterrupt(1, 1);

        } else {
            PANIC();
        }

        return 0;
    }

# endif

#else // UAVCAN_STM32_NUTTX

#if !defined(CAN1_TX_IRQHandler) ||\
    !defined(CAN1_RX0_IRQHandler) ||\
    !defined(CAN1_RX1_IRQHandler)
# error "Misconfigured build"
#endif

    UAVCAN_STM32_IRQ_HANDLER(CAN1_TX_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN1_TX_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleTxInterrupt(0);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

    UAVCAN_STM32_IRQ_HANDLER(CAN1_RX0_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN1_RX0_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleRxInterrupt(0, 0);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

    UAVCAN_STM32_IRQ_HANDLER(CAN1_RX1_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN1_RX1_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleRxInterrupt(0, 1);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

# if UAVCAN_STM32_NUM_IFACES > 1

#if !defined(CAN2_TX_IRQHandler) ||\
    !defined(CAN2_RX0_IRQHandler) ||\
    !defined(CAN2_RX1_IRQHandler)
# error "Misconfigured build"
#endif

    UAVCAN_STM32_IRQ_HANDLER(CAN2_TX_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN2_TX_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleTxInterrupt(1);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

    UAVCAN_STM32_IRQ_HANDLER(CAN2_RX0_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN2_RX0_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleRxInterrupt(1, 0);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

    UAVCAN_STM32_IRQ_HANDLER(CAN2_RX1_IRQHandler);
    UAVCAN_STM32_IRQ_HANDLER(CAN2_RX1_IRQHandler)
    {
        UAVCAN_STM32_IRQ_PROLOGUE();
        uavcan_stm32::handleRxInterrupt(1, 1);
        UAVCAN_STM32_IRQ_EPILOGUE();
    }

# endif
#endif // UAVCAN_STM32_NUTTX

} // extern "C"