DataFlash.cpp

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#include "DataFlash.h"

#include "DataFlash_Backend.h"

#include "DataFlash_File.h"
#include "DataFlash_File_sd.h"
#include "DataFlash_MAVLink.h"
#include <GCS_MAVLink/GCS.h>
#if CONFIG_HAL_BOARD == HAL_BOARD_F4LIGHT
#include "DataFlash_Revo.h"
#endif


DataFlash_Class *DataFlash_Class::_instance;

extern const AP_HAL::HAL& hal;

const AP_Param::GroupInfo DataFlash_Class::var_info[] = {
    // @Param: _BACKEND_TYPE
    // @DisplayName: DataFlash Backend Storage type
    // @Description: 0 for None, 1 for File, 2 for dataflash mavlink, 3 for both file and dataflash
    // @Values: 0:None,1:File,2:MAVLink,3:BothFileAndMAVLink
    // @User: Standard
    AP_GROUPINFO("_BACKEND_TYPE",  0, DataFlash_Class, _params.backend_types,       DATAFLASH_BACKEND_FILE),

    // @Param: _FILE_BUFSIZE
    // @DisplayName: Maximum DataFlash File Backend buffer size (in kilobytes)
    // @Description: The DataFlash_File backend uses a buffer to store data before writing to the block device.  Raising this value may reduce "gaps" in your SD card logging.  This buffer size may be reduced depending on available memory.  PixHawk requires at least 4 kilobytes.  Maximum value available here is 64 kilobytes.
    // @User: Standard
    AP_GROUPINFO("_FILE_BUFSIZE",  1, DataFlash_Class, _params.file_bufsize,       16),

    // @Param: _DISARMED
    // @DisplayName: Enable logging while disarmed
    // @Description: If LOG_DISARMED is set to 1 then logging will be enabled while disarmed. This can make for very large logfiles but can help a lot when tracking down startup issues
    // @Values: 0:Disabled,1:Enabled
    // @User: Standard
    AP_GROUPINFO("_DISARMED",  2, DataFlash_Class, _params.log_disarmed,       0),

    // @Param: _REPLAY
    // @DisplayName: Enable logging of information needed for Replay
    // @Description: If LOG_REPLAY is set to 1 then the EKF2 state estimator will log detailed information needed for diagnosing problems with the Kalman filter. It is suggested that you also raise LOG_FILE_BUFSIZE to give more buffer space for logging and use a high quality microSD card to ensure no sensor data is lost
    // @Values: 0:Disabled,1:Enabled
    // @User: Standard
    AP_GROUPINFO("_REPLAY",  3, DataFlash_Class, _params.log_replay,       0),

    // @Param: _FILE_DSRMROT
    // @DisplayName: Stop logging to current file on disarm
    // @Description: When set, the current log file is closed when the vehicle is disarmed.  If LOG_DISARMED is set then a fresh log will be opened.
    // @Values: 0:Disabled,1:Enabled
    // @User: Standard
    AP_GROUPINFO("_FILE_DSRMROT",  4, DataFlash_Class, _params.file_disarm_rot,       0),

    // @Param: _MAV_BUFSIZE
    // @DisplayName: Maximum DataFlash MAVLink Backend buffer size
    // @Description: Maximum amount of memory to allocate to DataFlash-over-mavlink
    // @User: Advanced
    // @Units: kB
    AP_GROUPINFO("_MAV_BUFSIZE",  5, DataFlash_Class, _params.mav_bufsize,       8),

    AP_GROUPEND
};

#define streq(x, y) (!strcmp(x, y))

DataFlash_Class::DataFlash_Class(const char *firmware_string, const AP_Int32 &log_bitmask)
    : _firmware_string(firmware_string)
    , _log_bitmask(log_bitmask)
{
    AP_Param::setup_object_defaults(this, var_info);
    if (_instance != nullptr) {
        AP_HAL::panic("DataFlash must be singleton");
    }

    _instance = this;
}

void DataFlash_Class::Init(const struct LogStructure *structures, uint8_t num_types)
{
    gcs().send_text(MAV_SEVERITY_INFO, "Preparing log system");
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    validate_structures(structures, num_types);
    dump_structures(structures, num_types);
#endif
    if (_next_backend == DATAFLASH_MAX_BACKENDS) {
        AP_HAL::panic("Too many backends");
        return;
    }
    _num_types = num_types;
    _structures = structures;

#if defined(HAL_BOARD_LOG_DIRECTORY)
 #if HAL_OS_POSIX_IO || HAL_OS_FATFS_IO
    if (_params.backend_types == DATAFLASH_BACKEND_FILE ||
        _params.backend_types == DATAFLASH_BACKEND_BOTH) {
        DFMessageWriter_DFLogStart *message_writer =
            new DFMessageWriter_DFLogStart(_firmware_string);
        if (message_writer != nullptr)  {
            backends[_next_backend] = new DataFlash_File(*this,
                                                         message_writer,
                                                         HAL_BOARD_LOG_DIRECTORY);
        }
        if (backends[_next_backend] == nullptr) {
            hal.console->printf("Unable to open DataFlash_File");
        } else {
            _next_backend++;
        }
    }
 #elif CONFIG_HAL_BOARD == HAL_BOARD_F4LIGHT 

    if (_params.backend_types == DATAFLASH_BACKEND_FILE ||
        _params.backend_types == DATAFLASH_BACKEND_BOTH) {

        DFMessageWriter_DFLogStart *message_writer =
            new DFMessageWriter_DFLogStart(_firmware_string);
        if (message_writer != nullptr)  {

  #if defined(BOARD_SDCARD_NAME) || defined(BOARD_DATAFLASH_FATFS)
            backends[_next_backend] = new DataFlash_File(*this, message_writer, HAL_BOARD_LOG_DIRECTORY);
  #else
            backends[_next_backend] = new DataFlash_Revo(*this, message_writer); // restore dataflash logs
  #endif
        }

        if (backends[_next_backend] == nullptr) {
            printf("Unable to open DataFlash_Revo");
        } else {
            _next_backend++;
        }
    }
 #endif
#endif // HAL_BOARD_LOG_DIRECTORY

#if DATAFLASH_MAVLINK_SUPPORT
    if (_params.backend_types == DATAFLASH_BACKEND_MAVLINK ||
        _params.backend_types == DATAFLASH_BACKEND_BOTH) {
        if (_next_backend == DATAFLASH_MAX_BACKENDS) {
            AP_HAL::panic("Too many backends");
            return;
        }
        DFMessageWriter_DFLogStart *message_writer =
            new DFMessageWriter_DFLogStart(_firmware_string);
        if (message_writer != nullptr)  {
            backends[_next_backend] = new DataFlash_MAVLink(*this,
                                                            message_writer);
        }
        if (backends[_next_backend] == nullptr) {
            hal.console->printf("Unable to open DataFlash_MAVLink");
        } else {
            _next_backend++;
        }
    }
#endif

    for (uint8_t i=0; i<_next_backend; i++) {
        backends[i]->Init();
    }

    Prep();

    EnableWrites(true);

    gcs().send_text(MAV_SEVERITY_INFO, "Prepared log system");
}

#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
#include <stdio.h>

#define DEBUG_LOG_STRUCTURES 0

extern const AP_HAL::HAL& hal;
#define Debug(fmt, args ...)  do {hal.console->printf("%s:%d: " fmt "\n", __FUNCTION__, __LINE__, ## args); hal.scheduler->delay(1); } while(0)

static uint8_t count_commas(const char *string)
{
    uint8_t ret = 0;
    for (uint8_t i=0; i<strlen(string); i++) {
        if (string[i] == ',') {
            ret++;
        }
    }
    return ret;
}

const char* DataFlash_Class::unit_name(const uint8_t unit_id)
{
    for(uint8_t i=0; i<unit_id; i++) {
        if (_units[i].ID == unit_id) {
            return _units[i].unit;
        }
    }
    return NULL;
}

double DataFlash_Class::multiplier_name(const uint8_t multiplier_id)
{
    for(uint8_t i=0; i<multiplier_id; i++) {
        if (_multipliers[i].ID == multiplier_id) {
            return _multipliers[i].multiplier;
        }
    }
    // Should we abort here?
    return 1.0f;
}

void DataFlash_Class::dump_structure_field(const struct LogStructure *logstructure, const char *label, const uint8_t fieldnum)
{
    ::fprintf(stderr, "  %s (%s)*(%f)\n", label, unit_name(logstructure->units[fieldnum]), multiplier_name(logstructure->multipliers[fieldnum]));
}

void DataFlash_Class::dump_structures(const struct LogStructure *logstructures, const uint8_t num_types)
{
#if DEBUG_LOG_STRUCTURES
    for (uint16_t i=0; i<num_types; i++) {
        const struct LogStructure *logstructure = &logstructures[i];
        ::fprintf(stderr, "%s\n", logstructure->name);
        char label[32] = { };
        uint8_t labeloffset = 0;
        int8_t fieldnum = 0;
        for (uint8_t j=0; j<strlen(logstructure->labels); j++) {
            char labelchar = logstructure->labels[j];
            if (labelchar == '\0') {
                break;
            }
            if (labelchar == ',') {
                dump_structure_field(logstructure, label, fieldnum);
                fieldnum++;
                labeloffset = 0;
                memset(label, '\0', 32);
            } else {
                label[labeloffset++] = labelchar;
            }
        }
        dump_structure_field(logstructure, label, fieldnum);
        ::fprintf(stderr, "\n"); // just add a CR to the output
    }
#endif
}

bool DataFlash_Class::validate_structure(const struct LogStructure *logstructure, const int16_t offset)
{
    bool passed = true;

#if DEBUG_LOG_STRUCTURES
    Debug("offset=%d ID=%d NAME=%s\n", offset, logstructure->msg_type, logstructure->name);
#endif

    // fields must be null-terminated
#define CHECK_ENTRY(fieldname,fieldname_s,fieldlen)                     \
    do {                                                                \
        if (strnlen(logstructure->fieldname, fieldlen) > fieldlen-1) {  \
            Debug("Message " fieldname_s " not NULL-terminated or too long"); \
            passed = false;                                             \
        }                                                               \
    } while (false)
    CHECK_ENTRY(name, "name", LS_NAME_SIZE);
    CHECK_ENTRY(format, "format", LS_FORMAT_SIZE);
    CHECK_ENTRY(labels, "labels", LS_LABELS_SIZE);
    CHECK_ENTRY(units, "units", LS_UNITS_SIZE);
    CHECK_ENTRY(multipliers, "multipliers", LS_MULTIPLIERS_SIZE);
#undef CHECK_ENTRY

    // ensure each message ID is only used once
    if (seen_ids[logstructure->msg_type]) {
        Debug("ID %d used twice (LogStructure offset=%d)", logstructure->msg_type, offset);
        passed = false;
    }
    seen_ids[logstructure->msg_type] = true;

    // ensure we have enough labels to cover columns
    uint8_t fieldcount = strlen(logstructure->format);
    uint8_t labelcount = count_commas(logstructure->labels)+1;
    if (fieldcount != labelcount) {
        Debug("fieldcount=%u does not match labelcount=%u",
              fieldcount, labelcount);
        passed = false;
    }

    // check that the structure is of an appropriate length to take fields
    const int16_t msg_len = Log_Write_calc_msg_len(logstructure->format);
    if (msg_len != logstructure->msg_len) {
        Debug("Calculated message length for (%s) based on format field (%s) does not match structure size (%d != %u)", logstructure->name, logstructure->format, msg_len, logstructure->msg_len);
        passed = false;
    }

    // ensure we have units for each field:
    if (strlen(logstructure->units) != fieldcount) {
        Debug("fieldcount=%u does not match unitcount=%lu",
              fieldcount, strlen(logstructure->units));
        passed = false;
    }

    // ensure we have multipliers for each field
    if (strlen(logstructure->multipliers) != fieldcount) {
        Debug("fieldcount=%u does not match multipliercount=%lu",
              fieldcount, strlen(logstructure->multipliers));
        passed = false;
    }

    // ensure the FMTU messages reference valid units
    for (uint8_t j=0; j<strlen(logstructure->units); j++) {
        char logunit = logstructure->units[j];
        uint8_t k;
        for (k=0; k<_num_units; k++) {
            if (logunit == _units[k].ID) {
                // found this one
                break;
            }
        }
        if (k == _num_units) {
            Debug("invalid unit=%c", logunit);
            passed = false;
        }
    }

    // ensure the FMTU messages reference valid multipliers
    for (uint8_t j=0; j<strlen(logstructure->multipliers); j++) {
        char logmultiplier = logstructure->multipliers[j];
        uint8_t k;
        for (k=0; k<_num_multipliers; k++) {
            if (logmultiplier == _multipliers[k].ID) {
                // found this one
                break;
            }
        }
        if (k == _num_multipliers) {
            Debug("invalid multiplier=%c", logmultiplier);
            passed = false;
        }
    }
    return passed;
}

void DataFlash_Class::validate_structures(const struct LogStructure *logstructures, const uint8_t num_types)
{
    Debug("Validating structures");
    bool passed = true;

    for (uint16_t i=0; i<num_types; i++) {
        const struct LogStructure *logstructure = &logstructures[i];
        passed = validate_structure(logstructure, i) && passed;
    }
    if (!passed) {
        Debug("Log structures are invalid");
        abort();
    }
}

#endif // CONFIG_HAL_BOARD == HAL_BOARD_SITL

const struct LogStructure *DataFlash_Class::structure(uint16_t num) const
{
    return &_structures[num];
}

bool DataFlash_Class::logging_present() const
{
    return _next_backend != 0;
}
bool DataFlash_Class::logging_enabled() const
{
    if (_next_backend == 0) {
        return false;
    }
    for (uint8_t i=0; i<_next_backend; i++) {
        if (backends[i]->logging_enabled()) {
            return true;
        }
    }
    return false;
}
bool DataFlash_Class::logging_failed() const
{
    if (_next_backend < 1) {
        // we should not have been called!
        return true;
    }
    for (uint8_t i=0; i<_next_backend; i++) {
        if (backends[i]->logging_failed()) {
            return true;
        }
    }
    return false;
}

void DataFlash_Class::Log_Write_MessageF(const char *fmt, ...)
{
    char msg[64] {};

    va_list ap;
    va_start(ap, fmt);
    hal.util->vsnprintf(msg, sizeof(msg), fmt, ap);
    va_end(ap);

    Log_Write_Message(msg);
}

void DataFlash_Class::backend_starting_new_log(const DataFlash_Backend *backend)
{
    for (uint8_t i=0; i<_next_backend; i++) {
        if (backends[i] == backend) { // pointer comparison!
            // reset sent masks
            for (struct log_write_fmt *f = log_write_fmts; f; f=f->next) {
                f->sent_mask &= ~(1<<i);
            }
            break;
        }
    }
}

bool DataFlash_Class::should_log(const uint32_t mask) const
{
    if (!(mask & _log_bitmask)) {
        return false;
    }
    if (!vehicle_is_armed() && !log_while_disarmed()) {
        return false;
    }
    if (in_log_download()) {
        return false;
    }
    if (_next_backend == 0) {
        return false;
    }
    return true;
}

const struct UnitStructure *DataFlash_Class::unit(uint16_t num) const
{
    return &_units[num];
}

const struct MultiplierStructure *DataFlash_Class::multiplier(uint16_t num) const
{
    return &log_Multipliers[num];
}

#define FOR_EACH_BACKEND(methodcall)              \
    do {                                          \
        for (uint8_t i=0; i<_next_backend; i++) { \
            backends[i]->methodcall;              \
        }                                         \
    } while (0)

void DataFlash_Class::PrepForArming()
{
    FOR_EACH_BACKEND(PrepForArming());
}

void DataFlash_Class::setVehicle_Startup_Log_Writer(vehicle_startup_message_Log_Writer writer)
{
    _vehicle_messages = writer;
}

void DataFlash_Class::set_vehicle_armed(const bool armed_state)
{
    if (armed_state == _armed) {
        // no change in status
        return;
    }
    _armed = armed_state;

    if (!_armed) {
        // went from armed to disarmed
        FOR_EACH_BACKEND(vehicle_was_disarmed());
    }

}


void DataFlash_Class::set_mission(const AP_Mission *mission) {
    FOR_EACH_BACKEND(set_mission(mission));
}

// start functions pass straight through to backend:
void DataFlash_Class::WriteBlock(const void *pBuffer, uint16_t size) {
    FOR_EACH_BACKEND(WriteBlock(pBuffer, size));
}

void DataFlash_Class::WriteCriticalBlock(const void *pBuffer, uint16_t size) {
    FOR_EACH_BACKEND(WriteCriticalBlock(pBuffer, size));
}

void DataFlash_Class::WritePrioritisedBlock(const void *pBuffer, uint16_t size, bool is_critical) {
    FOR_EACH_BACKEND(WritePrioritisedBlock(pBuffer, size, is_critical));
}

// change me to "DoTimeConsumingPreparations"?
void DataFlash_Class::EraseAll() {
    FOR_EACH_BACKEND(EraseAll());
}
// change me to "LoggingAvailable"?
bool DataFlash_Class::CardInserted(void) {
    for (uint8_t i=0; i< _next_backend; i++) {
        if (backends[i]->CardInserted()) {
            return true;
        }
    }
    return false;
}

void DataFlash_Class::Prep() {
    FOR_EACH_BACKEND(Prep());
}

void DataFlash_Class::StopLogging()
{
    FOR_EACH_BACKEND(stop_logging());
}

uint16_t DataFlash_Class::find_last_log() const {
    if (_next_backend == 0) {
        return 0;
    }
    return backends[0]->find_last_log();
}
void DataFlash_Class::get_log_boundaries(uint16_t log_num, uint16_t & start_page, uint16_t & end_page) {
    if (_next_backend == 0) {
        return;
    }
    backends[0]->get_log_boundaries(log_num, start_page, end_page);
}
void DataFlash_Class::get_log_info(uint16_t log_num, uint32_t &size, uint32_t &time_utc) {
    if (_next_backend == 0) {
        return;
    }
    backends[0]->get_log_info(log_num, size, time_utc);
}
int16_t DataFlash_Class::get_log_data(uint16_t log_num, uint16_t page, uint32_t offset, uint16_t len, uint8_t *data) {
    if (_next_backend == 0) {
        return 0;
    }
    return backends[0]->get_log_data(log_num, page, offset, len, data);
}
uint16_t DataFlash_Class::get_num_logs(void) {
    if (_next_backend == 0) {
        return 0;
    }
    return backends[0]->get_num_logs();
}

/* we're started if any of the backends are started */
bool DataFlash_Class::logging_started(void) {
    for (uint8_t i=0; i< _next_backend; i++) {
        if (backends[i]->logging_started()) {
            return true;
        }
    }
    return false;
}

void DataFlash_Class::handle_mavlink_msg(GCS_MAVLINK &link, mavlink_message_t* msg)
{
    switch (msg->msgid) {
    case MAVLINK_MSG_ID_REMOTE_LOG_BLOCK_STATUS:
        FOR_EACH_BACKEND(remote_log_block_status_msg(link.get_chan(), msg));
        break;
    case MAVLINK_MSG_ID_LOG_REQUEST_LIST:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_REQUEST_DATA:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_ERASE:
        FALLTHROUGH;
    case MAVLINK_MSG_ID_LOG_REQUEST_END:
        handle_log_message(link, msg);
        break;
    }
}

void DataFlash_Class::periodic_tasks() {
    handle_log_send();
    FOR_EACH_BACKEND(periodic_tasks());
}

#if CONFIG_HAL_BOARD == HAL_BOARD_SITL || CONFIG_HAL_BOARD == HAL_BOARD_LINUX
    // currently only DataFlash_File support this:
void DataFlash_Class::flush(void) {
     FOR_EACH_BACKEND(flush());
}
#endif


void DataFlash_Class::Log_Write_EntireMission(const AP_Mission &mission)
{
    FOR_EACH_BACKEND(Log_Write_EntireMission(mission));
}

void DataFlash_Class::Log_Write_Message(const char *message)
{
    FOR_EACH_BACKEND(Log_Write_Message(message));
}

void DataFlash_Class::Log_Write_Mode(uint8_t mode, uint8_t reason)
{
    FOR_EACH_BACKEND(Log_Write_Mode(mode, reason));
}

void DataFlash_Class::Log_Write_Parameter(const char *name, float value)
{
    FOR_EACH_BACKEND(Log_Write_Parameter(name, value));
}

void DataFlash_Class::Log_Write_Mission_Cmd(const AP_Mission &mission,
                                            const AP_Mission::Mission_Command &cmd)
{
    FOR_EACH_BACKEND(Log_Write_Mission_Cmd(mission, cmd));
}

uint32_t DataFlash_Class::num_dropped() const
{
    if (_next_backend == 0) {
        return 0;
    }
    return backends[0]->num_dropped();
}


// end functions pass straight through to backend

void DataFlash_Class::internal_error() const {
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    AP_HAL::panic("Internal DataFlash error");
#endif
}

/* Log_Write support */
void DataFlash_Class::Log_Write(const char *name, const char *labels, const char *fmt, ...)
{
    va_list arg_list;

    va_start(arg_list, fmt);
    Log_WriteV(name, labels, nullptr, nullptr, fmt, arg_list);
    va_end(arg_list);
}

void DataFlash_Class::Log_Write(const char *name, const char *labels, const char *units, const char *mults, const char *fmt, ...)
{
    va_list arg_list;

    va_start(arg_list, fmt);
    Log_WriteV(name, labels, units, mults, fmt, arg_list);
    va_end(arg_list);
}

void DataFlash_Class::Log_WriteV(const char *name, const char *labels, const char *units, const char *mults, const char *fmt, va_list arg_list)
{
    struct log_write_fmt *f = msg_fmt_for_name(name, labels, units, mults, fmt);
    if (f == nullptr) {
        // unable to map name to a messagetype; could be out of
        // msgtypes, could be out of slots, ...
        internal_error();
        return;
    }

    for (uint8_t i=0; i<_next_backend; i++) {
        if (!(f->sent_mask & (1U<<i))) {
            if (!backends[i]->Log_Write_Emit_FMT(f->msg_type)) {
                continue;
            }
            f->sent_mask |= (1U<<i);
        }
        va_list arg_copy;
        va_copy(arg_copy, arg_list);
        backends[i]->Log_Write(f->msg_type, arg_copy);
        va_end(arg_copy);
    }
}


#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
void DataFlash_Class::assert_same_fmt_for_name(const DataFlash_Class::log_write_fmt *f,
                                               const char *name,
                                               const char *labels,
                                               const char *units,
                                               const char *mults,
                                               const char *fmt) const
{
    bool passed = true;
    if (!streq(f->name, name)) {
        // why exactly were we called?!
        Debug("format names differ (%s) != (%s)", f->name, name);
        passed = false;
    }
    if (!streq(f->labels, labels)) {
        Debug("format labels differ (%s) vs (%s)", f->labels, labels);
        passed = false;
    }
    if ((f->units != nullptr && units == nullptr) ||
        (f->units == nullptr && units != nullptr) ||
        (units !=nullptr && !streq(f->units, units))) {
        Debug("format units differ (%s) vs (%s)",
              (f->units ? f->units : "nullptr"),
              (units ? units : "nullptr"));
        passed = false;
    }
    if ((f->mults != nullptr && mults == nullptr) ||
        (f->mults == nullptr && mults != nullptr) ||
        (mults != nullptr && !streq(f->mults, mults))) {
        Debug("format mults differ (%s) vs (%s)",
              (f->mults ? f->mults : "nullptr"),
              (mults ? mults : "nullptr"));
        passed = false;
    }
    if (!streq(f->fmt, fmt)) {
        Debug("format fmt differ (%s) vs (%s)",
              (f->fmt ? f->fmt : "nullptr"),
              (fmt ? fmt : "nullptr"));
        passed = false;
    }
    if (!passed) {
        Debug("Format definition must be consistent for every call of Log_Write");
        abort();
    }
}
#endif

DataFlash_Class::log_write_fmt *DataFlash_Class::msg_fmt_for_name(const char *name, const char *labels, const char *units, const char *mults, const char *fmt)
{
    struct log_write_fmt *f;
    for (f = log_write_fmts; f; f=f->next) {
        if (f->name == name) { // ptr comparison
            // already have an ID for this name:
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
            assert_same_fmt_for_name(f, name, labels, units, mults, fmt);
#endif
            return f;
        }
    }
    f = (struct log_write_fmt *)calloc(1, sizeof(*f));
    if (f == nullptr) {
        // out of memory
        return nullptr;
    }
    // no message type allocated for this name.  Try to allocate one:
    int16_t msg_type = find_free_msg_type();
    if (msg_type == -1) {
        free(f);
        return nullptr;
    }
    f->msg_type = msg_type;
    f->name = name;
    f->fmt = fmt;
    f->labels = labels;
    f->units = units;
    f->mults = mults;

    int16_t tmp = Log_Write_calc_msg_len(fmt);
    if (tmp == -1) {
        free(f);
        return nullptr;
    }

    f->msg_len = tmp;

    // add to front of list
    f->next = log_write_fmts;
    log_write_fmts = f;

#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
    char ls_name[LS_NAME_SIZE] = {};
    char ls_format[LS_FORMAT_SIZE] = {};
    char ls_labels[LS_LABELS_SIZE] = {};
    char ls_units[LS_UNITS_SIZE] = {};
    char ls_multipliers[LS_MULTIPLIERS_SIZE] = {};
    struct LogStructure ls = {
        f->msg_type,
        f->msg_len,
        ls_name,
        ls_format,
        ls_labels,
        ls_units,
        ls_multipliers
    };
    memcpy((char*)ls_name, f->name, MIN(sizeof(ls_name), strlen(f->name)));
    memcpy((char*)ls_format, f->fmt, MIN(sizeof(ls_format), strlen(f->fmt)));
    memcpy((char*)ls_labels, f->labels, MIN(sizeof(ls_labels), strlen(f->labels)));
    if (f->units != nullptr) {
        memcpy((char*)ls_units, f->units, MIN(sizeof(ls_units), strlen(f->units)));
    } else {
        memset((char*)ls_units, '?', MIN(sizeof(ls_format), strlen(f->fmt)));
    }
    if (f->mults != nullptr) {
        memcpy((char*)ls_multipliers, f->mults, MIN(sizeof(ls_multipliers), strlen(f->mults)));
    } else {
        memset((char*)ls_multipliers, '?', MIN(sizeof(ls_format), strlen(f->fmt)));
    }
    validate_structure(&ls, (int16_t)-1);
#endif

    return f;
}

// returns true if the msg_type is already taken
bool DataFlash_Class::msg_type_in_use(const uint8_t msg_type) const
{
    // check static list of messages (e.g. from LOG_BASE_STRUCTURES)
    // check the write format types to see if we've used this one
    for (uint16_t i=0; i<_num_types;i++) {
        if (structure(i)->msg_type == msg_type) {
            // in use
            return true;
        }
    }

    struct log_write_fmt *f;
    for (f = log_write_fmts; f; f=f->next) {
        if (f->msg_type == msg_type) {
            return true;
        }
    }
    return false;
}

// find a free message type
int16_t DataFlash_Class::find_free_msg_type() const
{
    // avoid using 255 here; perhaps we want to use it to extend things later
    for (uint16_t msg_type=254; msg_type>0; msg_type--) { // more likely to be free at end
        if (! msg_type_in_use(msg_type)) {
            return msg_type;
        }
    }
    return -1;
}

/*
 * It is assumed that logstruct's char* variables are valid strings of
 * maximum lengths for those fields (given in LogStructure.h e.g. LS_NAME_SIZE)
 */
bool DataFlash_Class::fill_log_write_logstructure(struct LogStructure &logstruct, const uint8_t msg_type) const
{
    // find log structure information corresponding to msg_type:
    struct log_write_fmt *f;
    for (f = log_write_fmts; f; f=f->next) {
        if(f->msg_type == msg_type) {
            break;
        }
    }

    if (!f) {
        return false;
    }

    logstruct.msg_type = msg_type;
    strncpy((char*)logstruct.name, f->name, LS_NAME_SIZE);
    strncpy((char*)logstruct.format, f->fmt, LS_FORMAT_SIZE);
    strncpy((char*)logstruct.labels, f->labels, LS_LABELS_SIZE);
    if (f->units != nullptr) {
        strncpy((char*)logstruct.units, f->units, LS_UNITS_SIZE);
    } else {
        memset((char*)logstruct.units, '\0', LS_UNITS_SIZE);
        memset((char*)logstruct.units, '?', MIN(LS_UNITS_SIZE,strlen(logstruct.format)));
    }
    if (f->mults != nullptr) {
        strncpy((char*)logstruct.multipliers, f->mults, LS_MULTIPLIERS_SIZE);
    } else {
        memset((char*)logstruct.multipliers, '\0', LS_MULTIPLIERS_SIZE);
        memset((char*)logstruct.multipliers, '?', MIN(LS_MULTIPLIERS_SIZE, strlen(logstruct.format)));
        // special magic to set units/mults for TimeUS, by far and
        // away the most common first field
        if (!strncmp(logstruct.labels, "TimeUS,", MIN(LS_LABELS_SIZE, strlen("TimeUS,")))) {
            ((char*)(logstruct.units))[0] = 's';
            ((char*)(logstruct.multipliers))[0] = 'F';
        }
    }
    logstruct.msg_len = f->msg_len;
    return true;
}

/* calculate the length of output of a format string.  Note that this
 * returns an int16_t; if it returns -1 then an error has occurred.
 * This was mechanically converted from init_field_types in
 * Tools/Replay/MsgHandler.cpp */
int16_t DataFlash_Class::Log_Write_calc_msg_len(const char *fmt) const
{
    uint8_t len =  LOG_PACKET_HEADER_LEN;
    for (uint8_t i=0; i<strlen(fmt); i++) {
        switch(fmt[i]) {
        case 'a' : len += sizeof(int16_t[32]); break;
        case 'b' : len += sizeof(int8_t); break;
        case 'c' : len += sizeof(int16_t); break;
        case 'd' : len += sizeof(double); break;
        case 'e' : len += sizeof(int32_t); break;
        case 'f' : len += sizeof(float); break;
        case 'h' : len += sizeof(int16_t); break;
        case 'i' : len += sizeof(int32_t); break;
        case 'n' : len += sizeof(char[4]); break;
        case 'B' : len += sizeof(uint8_t); break;
        case 'C' : len += sizeof(uint16_t); break;
        case 'E' : len += sizeof(uint32_t); break;
        case 'H' : len += sizeof(uint16_t); break;
        case 'I' : len += sizeof(uint32_t); break;
        case 'L' : len += sizeof(int32_t); break;
        case 'M' : len += sizeof(uint8_t); break;
        case 'N' : len += sizeof(char[16]); break;
        case 'Z' : len += sizeof(char[64]); break;
        case 'q' : len += sizeof(int64_t); break;
        case 'Q' : len += sizeof(uint64_t); break;
        default:
#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
            AP_HAL::panic("Unknown format specifier (%c)", fmt[i]);
#endif
            return -1;
        }
    }
    return len;
}

/* End of Log_Write support */

#undef FOR_EACH_BACKEND

// Write information about a series of IMU readings to log:
bool DataFlash_Class::Log_Write_ISBH(const uint16_t seqno,
                                     const AP_InertialSensor::IMU_SENSOR_TYPE sensor_type,
                                     const uint8_t sensor_instance,
                                     const uint16_t mult,
                                     const uint16_t sample_count,
                                     const uint64_t sample_us,
                                     const float sample_rate_hz)
{
    if (_next_backend == 0) {
        return false;
    }
    struct log_ISBH pkt = {
        LOG_PACKET_HEADER_INIT(LOG_ISBH_MSG),
        time_us        : AP_HAL::micros64(),
        seqno          : seqno,
        sensor_type    : (uint8_t)sensor_type,
        instance       : sensor_instance,
        multiplier     : mult,
        sample_count   : sample_count,
        sample_us      : sample_us,
        sample_rate_hz : sample_rate_hz,
    };

    // only the first backend need succeed for us to be successful
    for (uint8_t i=1; i<_next_backend; i++) {
        backends[i]->WriteBlock(&pkt, sizeof(pkt));
    }

    return backends[0]->WriteBlock(&pkt, sizeof(pkt));
}


// Write a series of IMU readings to log:
bool DataFlash_Class::Log_Write_ISBD(const uint16_t isb_seqno,
                                     const uint16_t seqno,
                                     const int16_t x[32],
                                     const int16_t y[32],
                                     const int16_t z[32])
{
    if (_next_backend == 0) {
        return false;
    }
    struct log_ISBD pkt = {
        LOG_PACKET_HEADER_INIT(LOG_ISBD_MSG),
        time_us    : AP_HAL::micros64(),
        isb_seqno  : isb_seqno,
        seqno      : seqno
    };
    memcpy(pkt.x, x, sizeof(pkt.x));
    memcpy(pkt.y, y, sizeof(pkt.y));
    memcpy(pkt.z, z, sizeof(pkt.z));

    // only the first backend need succeed for us to be successful
    for (uint8_t i=1; i<_next_backend; i++) {
        backends[i]->WriteBlock(&pkt, sizeof(pkt));
    }

    return backends[0]->WriteBlock(&pkt, sizeof(pkt));
}