High speed UART with libuarte -> "Unexpected RX free input parameter"

[VGKilian]

Hi,

Currently I’m working on a device which is, on the one side connected to a smartphone via BLE and on the other side to another uC via UART.

Therefore, the UART speed is fixed to 1MB/s (without flow control). For this reason, I must use DMA to get the UART running.

We use the nRF52840 DK with the SDK 16.0.0.

I had a look to the example projects “ble_app_uart” and “libuarte”. Both projects fulfill our requirements to the BLE and UART connection.

I merged this projects and after some problems, it works just fine.

At the beginning it works just fine, but after some telegrams over the UART the "libUARTE_async: Unexpected RX free input parameter." messages appears.

The minimal time interval between two telegrams is 100ms.

What could cause this error?

How to fix it?

Best Regards,

Kilian Neubacher

[Sigurd]

Hi,

How many bytes are you sending ?

Could you try to increase the _rx_buf_size used in NRF_LIBUARTE_ASYNC_DEFINE() (default in the libuarte example is 255)

[VGKilian]

I'm not able to increase _rx_buf_size  because of line 584 in nrf_libuarte_drv.c.

ASSERT(len <= MAX_DMA_XFER_LEN);

In my case len ist 512 and MAX_DMA_XFER_LEN is 255. -> #define MAX_DMA_XFER_LEN    ((1UL << UARTE0_EASYDMA_MAXCNT_SIZE) - 1)

Any idea how to fix it?

[Sigurd]

VGKilian said:

Any idea how to fix it?

 Are you sure that you are using the nRF52840(pca10056) project ? Maybe you are using the nRF52832(pca10040) project ?

MAX_DMA_XFER_LEN for nRF52840 is 65535, but for nRF52832 it's 255.

[VGKilian]

I found the error.

The nrf_libuarte_async_rx_free function() was called in the wrong place.

Thanks for your help!!!

[VGKilian]

You are right i use the wrong project!

After placing nrf_libuarte_async_rx_free function at the right spot, every thing works fine.

Is it necessary to switch to right project?

[Sigurd]

Great!

VGKilian said:

Is it necessary to switch to right project?

Yes, you should use the pca10056 projects when using the nRF52840. The pca10056 projects are configured to use the correct register header files and startup code for the nRF52840.