Ring buffer or queue for different datatype

RE: Ring buffer or queue for different datatype

haakonsh — Tue, 20 Aug 2019 10:58:36 GMT

[quote user="Ali Rumane"]Is there a way I can get available length before copying so that I don't have to remove half written data or copy half data so that I can free (nrf_ringbuf_free) some data and then copy the data.[/quote]

There's no such functionality, you'll have to track the amount of data stored yourself.
As each call to nrf_ringbuf_cpy_put will return the length of written data you can increment a global counter variable when you write and decrement when you free. That way you can compare the counter variable to the ring buffer size and know how much space is free.

RE: Ring buffer or queue for different datatype

Ali Rumane — Mon, 19 Aug 2019 12:04:51 GMT

HI haakonsh,

Thank you for your help, I managed to implement it correctly.

NRF_RINGBUF_DEF(m_ringbuf, 8);

int main(void)
{
	ret_code_t err_code;
	
	nrf_ringbuf_init(&m_ringbuf);
	
	uint16_t data_in[] = {1024, 1025, 1026, 1027};
	size_t  len_in = sizeof(data_in);

	err_code = nrf_ringbuf_cpy_put(&m_ringbuf, (uint8_t*)data_in, &len_in);
	APP_ERROR_CHECK(err_code);
		
    uint16_t data_out[4];
    size_t  len_out = sizeof(data_out);

    err_code = nrf_ringbuf_cpy_get(&m_ringbuf, (uint8_t*)data_out, &len_out);
	APP_ERROR_CHECK(err_code);
}

I am facing another issue.

Let's say I have got 2 bytes of memory left and would like to copy 4 bytes of data. If I use

nrf_ringbuf_cpy_put, I will get available length or copied length after copying the data.

Is there a way I can get available length before copying so that I don't have to remove half written data or copy half data so that I can free (nrf_ringbuf_free) some data and then copy the data.

e.g.

NRF_RINGBUF_DEF(m_ringbuf, 8);

ring_bufer(1,2,3,4,5,6) // Data already present in buffer

{7,8,9,10} // New data to write

Since only two bytes are left, ring buffer will write 7&8 and return available length.

Regards

RE: Ring buffer or queue for different datatype

Ali Rumane — Mon, 05 Aug 2019 08:52:12 GMT

Hi,
Thank you for your help.

[quote userid="13562" url="~/f/nordic-q-a/50057/ring-buffer-or-queue-for-different-datatype/199859"]
I suggest you read up on Type Casting and Pointer Type Casting in C as it is fundamental in understanding your problem and its solution.[/quote]

Sure, I will be doing the same.

RE: Ring buffer or queue for different datatype

haakonsh — Mon, 22 Jul 2019 14:52:47 GMT

[quote user="Ali Rumane"]The nrf_ringbuf_cpy_put API accepts data as uint8_t, so I can't put any other datatype like uint16_t or something so how will it work for my application?[/quote]

You store an array of data no matter what type it is. Whether you access the data as uint8 or int16 won't change the data itself.

I suggest you read up on Type Casting and Pointer Type Casting in C as it is fundamental in understanding your problem and its solution.

see f.ex. https://stackoverflow.com/questions/17260527/what-are-the-rules-for-casting-pointers-in-c/17260931

[quote user="Ali Rumane"]Let's say I want to store 5 bytes data so do I deliberately need to store 0 or some other value so that data becomes 6 which is multiple of 2 and ignore while retrieving it?[/quote]

Int16's are exactly two bytes of data. If you want to store 5 uint8's then you will need 5x1 bytes, but if you want to store 5 int16's as uint8's it will require 5x2 bytes.

RE: Ring buffer or queue for different datatype

Ali Rumane — Mon, 22 Jul 2019 14:30:44 GMT

Thank you for your response.

I am little confused;

[quote userid="13562" url="~/f/nordic-q-a/50057/ring-buffer-or-queue-for-different-datatype/199754"]data is accessed as uint8 or int16 does not really matter[/quote]

The nrf_ringbuf_cpy_put API accepts data as uint8_t, so I can't put any other datatype like uint16_t or something so how will it work for my application?

ret_code_t nrf_ringbuf_cpy_put(nrf_ringbuf_t const * p_ringbuf,
                               uint8_t const * p_data,
                               size_t * p_length);

[quote userid="13562" url="~/f/nordic-q-a/50057/ring-buffer-or-queue-for-different-datatype/199754"]read and write to the ring buffer in multiples of two bytes[/quote]

Let's say I want to store 5 bytes data so do I deliberately need to store 0 or some other value so that data becomes 6 which is multiple of 2 and ignore while retrieving it?

Regards

RE: Ring buffer or queue for different datatype

haakonsh — Mon, 22 Jul 2019 11:29:33 GMT

From the queue buffer docs: "The queue library provides interrupt secure implementation of the circular buffer to store predefined objects".

Whether your data is accessed as uint8 or int16 does not really matter as long as you read and write to the ring buffer in multiples of two bytes, the data is still there.