This wrapper is intended to be a reasonable example of how to use the Timeslot interface that is built into the MPSL in Nordic's nRF Connect SDK. The objective is to open a recurring timeslot of a fixed length after a BLE connection has been established. Each timeslot has a fixed length and is opened once per Connection Interval. If a library like ESB is going to be used then a preprocessor symbol called TIMESLOT_CALLS_RADIO_IRQHANDLER can be set to call RADIO_IRQHandler directly from the MPSL_TIMESLOT_SIGNAL_RADIO signal. A "skipped" callback is also provided so proprietary networks can stay in sync when timeslots are blocked or cancelled.

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Implementation

Timeslots are synchronized to the active edge of radio notifications so they can follow along with the timing of the BLE connection's Connection Events. The radio notifications feature requires a hardware interrupt vector so a TIMESLOT_IRQN must be defined in timeslot.h (the default is QDEC_IRQn). The MPSL timeslot callback runs as a Zero Latency IRQ and benefits from a hardware interrupt vector so the TIMESLOT_IRQN is also used for lowering the priority of several MPSL interrupts.

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Usage

The timeslot_config struct and timeslot_cb structs are required.

#include <timeslot.h>
...
static void timeslot_err_cb(int err)
{
    LOG_ERR("Timeslot session error: %d", err);
}

static void timeslot_start_cb(void)
{
    LOG_DBG("Timeslot start");
}

static void timeslot_end_cb(void)
{
    LOG_DBG("Timeslot end");
}

static void timeslot_skipped_cb(uint8_t count)
{
    LOG_INF("Timeslot skipped: %d", count);
}

static void timeslot_stopped_cb(void)
{
    LOG_INF("Timeslot stopped");
}

#if !TIMESLOT_CALLS_RADIO_IRQHANDLER
static void radio_irq_cb(void)
{
    LOG_DBG("Radio_IRQHandler");
}
#endif

static struct timeslot_cb timeslot_callbacks = {
    .error     = timeslot_err_cb,
    .start     = timeslot_start_cb,
    .end       = timeslot_end_cb,
    .skipped   = timeslot_skipped_cb,
    .stopped   = timeslot_stopped_cb,
#if !TIMESLOT_CALLS_RADIO_IRQHANDLER
    .radio_irq = radio_irq_cb
#endif
};

static struct timeslot_config timeslot_config = TS_DEFAULT_CONFIG;
...
void main(void)
{
    int err = timeslot_open(&timeslot_config, &timeslot_callbacks);
    if (err) {
        LOG_ERR("timeslot_open failed (err: %d)", err);
    }
...

A good place to start requesting timeslots is after the BLE connection parameters have settled.

static void conn_param_update(struct bt_conn *conn, uint16_t interval, uint16_t latency, uint16_t timeout)
{
...
    int err = timeslot_start(500);
    if (err) {
        LOG_ERR("timeslot_start failed (err=%d)", err);
    }

If the connection parameters change during the connection then the current timeslots can be stopped so they can be restarted in the "stopped" callback.

next_interval = interval;
int err = timeslot_stop();
if (err) {
    LOG_ERR("timeslot_stop failed (err=%d)", err);
}