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]

Hi Siguard,

The amount of send data is not constant, but it is less then 100 bytes per telegram.

I tried to increase the _rx_buf_size to 512. After that the app_error_fault_handler() function is called short time after bootup.

Logging: 

<error> app: ERROR 3735928559 [Unknown error code] at [myFolder]\nRF5_SDK_16.0.0_98a08e2/componB

Sadly the error message is truncated.

Best Regards,

Kilian

[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!!!