Help me understand the operation of the NRF_RINGBUF module

Question

Hi!

I'm trying to figure out the nrf_ringbuf module, and would really appreciate some advice about its intended use case. The api exposes the following functions:

void 	nrf_ringbuf_init (nrf_ringbuf_t const *p_ringbuf)
 
ret_code_t 	nrf_ringbuf_alloc (nrf_ringbuf_t const *p_ringbuf, uint8_t **pp_data, size_t *p_length, bool start)
 
ret_code_t 	nrf_ringbuf_put (nrf_ringbuf_t const *p_ringbuf, size_t length)
 
ret_code_t 	nrf_ringbuf_cpy_put (nrf_ringbuf_t const *p_ringbuf, uint8_t const *p_data, size_t *p_length)
 
ret_code_t 	nrf_ringbuf_get (nrf_ringbuf_t const *p_ringbuf, uint8_t **pp_data, size_t *p_length, bool start)
 
ret_code_t 	nrf_ringbuf_free (nrf_ringbuf_t const *p_ringbuf, size_t length)
 
ret_code_t 	nrf_ringbuf_cpy_get (nrf_ringbuf_t const *p_ringbuf, uint8_t *p_data, size_t *p_length)

This is my current flow of execution:

Ask for space with nrf_ringbuffer_alloc( p_ringbuf, pp_data, p_length, false). This gives me a pointer to where I can write the amount of bytes that I've requested.

Write bytes to the allocated pointer location using memcpy( pp_data, inputBuffer, length )

Commit the bytes to the ring buffer using nrf_ringbuf_put( p_ringbuf, length)

...

Later pop things from the ring buffer using:

nrf_ringbuf_get ( p_ringbuf, pp_data, &length, false );

memcpy( inputBuffer, pp_data, length );

nrf_ringbuf_free( p_ringbuf, length );

However, I am getting an error, NRF_ERROR_INVALID_STATE, from line 94 of nrf_ringbuf.c:

 if (nrf_atomic_u32_fetch_sub(&p_ringbuf->p_cb->flag, 1 << WR_OFFSET) & (1 << WR_OFFSET))

I believe I am not using the api correctly, as I haven't understood the use case of nrf_ringbuf_cpy_put() and cpy_get() . Are these supposed to be called in-between alloc & put, and get & free? It is not very clear in the documentation. Please advise.

Cheers and all the best,
Rares Gosman

Igor · Answer

This works with SDK 15.2: #define MSG_LEN 20
#define BUFFER_SIZE 256 // 2^n !!!

NRF_RINGBUF_DEF(ring_buffer, BUFFER_SIZE); 

void initialize() {
 nrf_ringbuf_init(&ring_buffer);
}

void some_method() {
 uint8_t data_in[MSG_LEN];
 uint8_t data_out[MSG_LEN];
 size_t len_out = MSG_LEN;
 APP_ERROR_CHECK(nrf_ringbuf_cpy_put(&ring_buffer, data_in, ARRAY_SIZE(data_in)));
 // ...
 APP_ERROR_CHECK(nrf_ringbuf_cpy_get(&ring_buffer, data_out, &len_out));
}