Can i Use Ring Buffer from Zephyr in Uart Event Handler?

[Rajender]

Hi,

Im using nrf9160 based custom board, nrf sdk 1.5.1. with Zephyr

Im using Uart in DMA mode but have small doubts in implementation

1. what is the max size of buffer for DMA in UART (i need at least 2048 buffer, so is that possible)?

2. I want to collect this Uart data in Ring Buffer(zephyr/..../sys/ring_buffer.h), can i directly implement ring_buf_put() in Uart Event Handler?, i have tested and its working fine, but i need confirmation that is it good practice or do we have any work arround?

3. can i use k_poll_signal_raise() in envent handler?

 if( ring_buf_put(&evcRingBuf, (event->data.rx.buf + event->data.rx.offset), event->data.rx.len) < event->data.rx.len )
    {
        LOG_WRN("RingBuf write failed");
      }    
      
      k_poll_signal_raise(&EVCCommSignal, EVC_PORT_DATA);
    }

Best Regards

Rajender

[Håkon Alseth]

Hi Rajender,

 

1. what is the max size of buffer for DMA in UART (i need at least 2048 buffer, so is that possible)?

 The DMA count is 12 bits, so you can send/receive up to 4095 bytes:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/uarte.html?cp=2_0_0_5_18_8_47#register.TXD.MAXCNT

2. I want to collect this Uart data in Ring Buffer(zephyr/..../sys/ring_buffer.h), can i directly implement ring_buf_put() in Uart Event Handler?, i have tested and its working fine, but i need confirmation that is it good practice or do we have any work arround?

Yes, but you have to ensure that if there's multiple scenarios (ie. different functions) where you put data into the ring buffer, that you guard the function with a mutex or similar, as described in the documentation for the function:

https://docs.zephyrproject.org/latest/reference/data_structures/ring_buffers.html#c.ring_buf_put

 

3. can i use k_poll_signal_raise() in envent handler?

Yes, it should not be problematic.

 

Kind regards,

Håkon

[Rajender]

Hi Hakon,

Håkon Alseth said:

you guard the function with a mutex or similar, as described in the documentation for the function

That means i can use Semaphore lock/ mutex lock also in this Uart event handler right?

Best Regards

Rajender

[Håkon Alseth]

Hi,

 

Rajender said:

That means i can use Semaphore lock/ mutex lock also in this Uart event handler right?

My apologies, I forgot to mention this initially;

you should be very careful about locking semaphores in interrupts, as you shall always give a timeout that is not K_FOREVER:

https://docs.zephyrproject.org/latest/reference/kernel/synchronization/semaphores.html#c.k_sem_take

 

If you have multiple functions pushing data to this ring-buffer, you can consider moving logic from the interrupt to a workqueue item instead. 

 

Kind regards,

Håkon