FreeRTOS with libuarte: incompatibility between app_timer and app_timer_freertos?

Question

Hello,

I intend to use libuarte under FreeRTOS together with the SoftDevice (SDK 17.1.0). An app_timer is used for the RX timeout. I think there might be an incompatibility problem between app_timer and app_timer_freertos.

My application initializes the libuarte as follows:

NRF_LIBUARTE_ASYNC_DEFINE( xLibUarteCOM0, 0, 1, NRF_LIBUARTE_PERIPHERAL_NOT_USED, NRF_LIBUARTE_PERIPHERAL_NOT_USED, 255, 3 );
xErrCode = nrf_libuarte_async_init( ( nrf_libuarte_async_t * )&xLibUarteCOM0, &nrf_libuarte_async_config, pvUartEvtHandler, ( void * )pxLibUarte );

The macro NRF_LIBUARTE_ASYNC_DEFINE creates xLibUarteCOM0 as follows:

static const nrf_libuarte_async_t xLibUarteCOM0 = 
{ 
	.p_rx_pool = &xLibUarteCOM0_rx_pool, 
	.p_rx_queue = &xLibUarteCOM0_rxdata_queue, 
	.p_rtc = 0, 
	.p_timer = 0, 
	.p_app_timer = &xLibUarteCOM0_app_timer, 
	.p_app_timer_ctrl_blk = &xLibUarteCOM0_app_timer_ctrl_blk, 
	.p_libuarte = &xLibUarteCOM0_libuarte, 
	.p_ctrl_blk = &xLibUarteCOM0ctrl_blk, 
	.rx_buf_size = 255, 
};

with p_app_timer_t being a pointer to (a pointer to) a variable of type app_timer_t:

static const app_timer_id_t xLibUarteCOM0_app_timer = &xLibUarteCOM0_app_timer_data; 

typedef struct
{
	nrf_sortlist_item_t         list_item;     /**< Token used by sortlist. */
	uint64_t                    end_val;       /**< RTC counter value when timer expires or @ref APP_TIMER_IDLE_VAL. */
	uint32_t                    repeat_period; /**< Repeat period (0 if single shot mode). */
	app_timer_timeout_handler_t handler;       /**< User handler. */
	void *                      p_context;     /**< User context. */
	NRF_LOG_INSTANCE_PTR_DECLARE(p_log)        /**< Pointer to instance of the logger object (Conditionally compiled). */
} app_timer_t;

The structure is then initialized by the macro as:

static app_timer_t xLibUarteCOM0_app_timer_data = 
{ 
	.end_val = 0xFFFFFFFFFFFFFFFFULL, 
};

In the FreeRTOS version of app_timer_create() called from nrf_libuarte_async_init(), xLibUarteCOM0_app_timer_data gets overlaid by a different structure. It is recasted to app_timer_info_t:

app_timer_info_t * pinfo = (app_timer_info_t*)(*p_timer_id);

/**@brief This structure keeps information about osTimer.*/
typedef struct
{
	void                      * argument;
	TimerHandle_t               osHandle;
	app_timer_timeout_handler_t func;
	/**
	 * This member is to make sure that timer function is only called if timer is running.
	 * FreeRTOS may have timer running even after stop function is called,
	 * because it processes commands in Timer task and stopping function only puts command into the queue. */
	bool                        active;
	bool                        single_shot;
}app_timer_info_t;

Without further initialization of the structure, app_timer_create() then checks the value of pinfo->active and fails with NRF_ERROR_INVALID_STATE if true.

The pinfo->active variable, however, is part of the pre-initialized 64-bit end_val and has the value 0xff which evaluates to true (!= 0). Hence, the initialization fails.

A possible work-around (although not very clean) is to initialize end_val with 0:

app_timer_t *p_xLibUarteCOM0_app_timer_data = *xLibUarteCOM0.p_app_timer;
p_xLibUarteCOM0_app_timer_data->end_val = 0x0ULL;

Does my analysis sound corrected or is there a another issue somewhere?

Thanks,

Norbert

Susheel Nuguru · Accepted Answer

OK, then i will not try to push you to use other instances of RTC then, in that case let us go to your initial efforts and look at the issue. 
 
 I think the main issue here is that the helper macros in the NRF_LIBUARTE_ASYNC_DEFINE has not been designed to work with the freertos. 
 so probably you can initialize p_app_timer pointing zero initialized structure of app_timer_info_t instead as a clean workaround.