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Feb 20, 2019
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nRF52 serial: Tighten/simplify atomics #9616

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40 changes: 18 additions & 22 deletions targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/serial_api.c
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Original file line number Diff line number Diff line change
Expand Up @@ -138,8 +138,8 @@ typedef struct {
uint8_t buffer[NUMBER_OF_BANKS][DMA_BUFFER_SIZE];
uint32_t usage_counter;
uint8_t tx_data;
volatile uint8_t tx_in_progress;
volatile uint8_t rx_in_progress;
bool tx_in_progress;
bool rx_in_progress;
bool tx_asynch;
bool rx_asynch;
bool callback_posted;
Expand Down Expand Up @@ -252,7 +252,7 @@ static void nordic_nrf5_uart_callback_handler(uint32_t instance)
static void nordic_nrf5_uart_event_handler_endtx(int instance)
{
/* Release mutex. As the owner this call is safe. */
nordic_nrf5_uart_state[instance].tx_in_progress = 0;
core_util_atomic_store_bool(&nordic_nrf5_uart_state[instance].tx_in_progress, false);

/* Check if callback handler and Tx event mask is set. */
uart_irq_handler callback = (uart_irq_handler) nordic_nrf5_uart_state[instance].owner->handler;
Expand All @@ -275,8 +275,8 @@ static void nordic_nrf5_uart_event_handler_endtx(int instance)
static void nordic_nrf5_uart_event_handler_endtx_asynch(int instance)
{
/* Set Tx done and reset Tx mode to be not asynchronous. */
nordic_nrf5_uart_state[instance].tx_in_progress = 0;
nordic_nrf5_uart_state[instance].tx_asynch = false;
core_util_atomic_store_bool(&nordic_nrf5_uart_state[instance].tx_in_progress, false);

/* Cast handler to callback function pointer. */
void (*callback)(void) = (void (*)(void)) nordic_nrf5_uart_state[instance].owner->tx_handler;
Expand Down Expand Up @@ -482,8 +482,8 @@ static void nordic_nrf5_uart_event_handler_rxstarted(int instance)
static void nordic_nrf5_uart_event_handler_endrx_asynch(int instance)
{
/* Set Rx done and reset Rx mode to be not asynchronous. */
nordic_nrf5_uart_state[instance].rx_in_progress = 0;
nordic_nrf5_uart_state[instance].rx_asynch = false;
core_util_atomic_store_bool(&nordic_nrf5_uart_state[instance].rx_in_progress, false);

/* Cast handler to callback function pointer. */
void (*callback)(void) = (void (*)(void)) nordic_nrf5_uart_state[instance].owner->rx_handler;
Expand Down Expand Up @@ -1410,7 +1410,7 @@ int serial_writable(serial_t *obj)

int instance = uart_object->instance;

return ((nordic_nrf5_uart_state[instance].tx_in_progress == 0) &&
return (!core_util_atomic_load_bool(&nordic_nrf5_uart_state[instance].tx_in_progress) &&
(nrf_uarte_event_extra_check(nordic_nrf5_uart_register[instance], NRF_UARTE_EVENT_TXDRDY)));
}

Expand Down Expand Up @@ -1449,16 +1449,14 @@ int serial_tx_asynch(serial_t *obj, const void *tx, size_t tx_length, uint8_t tx

/**
* tx_in_progress acts like a mutex to ensure only one transmission can be active at a time.
* The flag is modified using the atomic compare-and-set function.
* The flag is modified using the atomic exchange function - only proceed when we see the
* flag clear and we set it to true.
*/
bool mutex = false;
bool old_mutex;

do {
uint8_t expected = 0;
uint8_t desired = 1;

mutex = core_util_atomic_cas_u8((uint8_t *) &nordic_nrf5_uart_state[instance].tx_in_progress, &expected, desired);
} while (mutex == false);
old_mutex = core_util_atomic_exchange_bool(&nordic_nrf5_uart_state[instance].tx_in_progress, true);
} while (old_mutex == true);

/* State variables. */
int result = 0;
Expand Down Expand Up @@ -1575,16 +1573,14 @@ void serial_rx_asynch(serial_t *obj, void *rx, size_t rx_length, uint8_t rx_widt

/**
* rx_in_progress acts like a mutex to ensure only one asynchronous reception can be active at a time.
* The flag is modified using the atomic compare-and-set function.
* The flag is modified using the atomic exchange function - only proceed when we see the
* flag clear and we set it to true.
*/
bool mutex = false;
bool old_mutex;

do {
uint8_t expected = 0;
uint8_t desired = 1;

mutex = core_util_atomic_cas_u8((uint8_t *) &nordic_nrf5_uart_state[instance].rx_in_progress, &expected, desired);
} while (mutex == false);
old_mutex = core_util_atomic_exchange_bool(&nordic_nrf5_uart_state[instance].rx_in_progress, true);
} while (old_mutex == true);

/* Store callback handler, mask and reset event value. */
obj->serial.rx_handler = handler;
Expand Down Expand Up @@ -1663,8 +1659,8 @@ void serial_tx_abort_asynch(serial_t *obj)
nrf_uarte_event_clear(nordic_nrf5_uart_register[instance], NRF_UARTE_EVENT_ENDTX);

/* Reset Tx flags. */
nordic_nrf5_uart_state[instance].tx_in_progress = 0;
nordic_nrf5_uart_state[instance].tx_asynch = false;
nordic_nrf5_uart_state[instance].tx_in_progress = false;

/* Force reconfiguration. */
obj->serial.update = true;
Expand All @@ -1691,8 +1687,8 @@ void serial_rx_abort_asynch(serial_t *obj)
core_util_critical_section_enter();

/* Reset Rx flags. */
nordic_nrf5_uart_state[obj->serial.instance].rx_in_progress = 0;
nordic_nrf5_uart_state[obj->serial.instance].rx_asynch = false;
nordic_nrf5_uart_state[obj->serial.instance].rx_in_progress = false;
obj->serial.rx_asynch = false;

/* Force reconfiguration. */
Expand Down