Help me understand the operation of the NRF_RINGBUF module

RE: Help me understand the operation of the NRF_RINGBUF module

Igor — Tue, 25 Sep 2018 09:02:10 GMT

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));
}

RE: Help me understand the operation of the NRF_RINGBUF module

haakonsh — Mon, 16 Apr 2018 11:12:18 GMT

The devs says its fixed in 15.1, scheduled mid-late Q2.

RE: Help me understand the operation of the NRF_RINGBUF module

haakonsh — Thu, 05 Apr 2018 14:11:03 GMT

Hey Rares,

No news I'm afraid :/

I'll poke the devs...

Cheers,

Håkon.

RE: Help me understand the operation of the NRF_RINGBUF module

rgosman — Tue, 27 Mar 2018 21:28:14 GMT

Hi Håkon,
Just wanted to follow up with you on this issue. I see that the change hasn't been made in SDK15, which launched last week. Is there any word back from the developer?

Cheers,
Rares

RE: Help me understand the operation of the NRF_RINGBUF module

haakonsh — Fri, 23 Feb 2018 09:48:22 GMT

I've reported the issue to the developers, but we might have to wait a while for a comment.

RE: Help me understand the operation of the NRF_RINGBUF module

rgosman — Wed, 21 Feb 2018 20:06:53 GMT

Hi Hakon,

Thanks for the advice. I updated to SDK14.2 and kept running into the same issue. I realized it was a problem with the nrf_ringbuf_cpy_get() function. The syntax being used with memcpy() is incorrect. It is provided like so in the SDK:

    if (length > trail)
    {
        memcpy(&p_ringbuf->p_buffer[masked_rd_idx], p_data, trail);
        length -= trail;
        masked_rd_idx = 0;
        p_data += trail;
    }
    memcpy(p_data, &p_ringbuf->p_buffer[masked_rd_idx], length);
    p_ringbuf->p_cb->rd_idx += *p_length;

Since this is a get() function, it should be filling the user-provided p_data buffer with data from the ring buffer. However, in this section of the code, where it handles the wrap-around behavior, the first memcpy() call is copying blank data from p_data into the ring buffer, and overwriting valid data. Line 212 of "nrf_ringbuf.c" should be:

memcpy(p_data, &p_ringbuf->p_buffer[masked_rd_idx], trail);

On the other hand, the nrf_ringbuf_cpy_put() command is fine:

    if (length > trail)
    {
        memcpy(&p_ringbuf->p_buffer[masked_wr_idx], p_data, trail);
        length -= trail;
        masked_wr_idx = 0;
        p_data += trail;
    }
    memcpy(&p_ringbuf->p_buffer[masked_wr_idx], p_data, length);
    p_ringbuf->p_cb->wr_idx += *p_length;

Notice that both memcpy() calls are being executed with the same order of parameters, since the destination is the ring buffer in the event of a put() command.

Please notify those in charge of this section of the SDK of this error.

Cheers,
Rares Gosman

RE: Help me understand the operation of the NRF_RINGBUF module

haakonsh — Wed, 21 Feb 2018 14:33:10 GMT

Hey Rares,
I believe you are using the API correctly. The library is experimental, and I see there's some changes between SDK14.0 and 14.2. Try 14.2 and see if that helps.

The 'copy' calls is used when you want the library to read and write directly to another buffer, instead of the one provided by the buffer allocation call.

Cheers,

Håkon.

RE: Help me understand the operation of the NRF_RINGBUF module

rgosman — Wed, 21 Feb 2018 01:00:52 GMT

Hello guys,

Any updates?

Cheers and all the best,
Rares