How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Thu, 21 Jul 2022 09:25:07 GMT

Does your call to app_uart_put() return any error codes?

Where are you calling this from? Is it called from interrupt context?

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Sami — Tue, 12 Jul 2022 05:24:01 GMT

Interesting issue that I'm seeing. Okay, so app_uart_get() is able to receive bytes over the RX line from a requesting app, however, app_uart_put() cannot send any data back in response. We have confirmed this by logic analyzer.

Here is my code:

int8_t transportSend( const uint16_t bufferSize, uint8_t *pBuffer )
{
    if ( pBuffer == NULL )
    {
        NRF_LOG_INFO("NULL?");
        return TRANSPORT_ERROR;
    }
    
    uint32_t status = NRF_SUCCESS;

    status = app_uart_put( START_BYTE );

    if (status != NRF_SUCCESS)
    {
        NRF_LOG_INFO("Failure in %s() @line %d", __FUNCTION__, __LINE__);
        return status;
    }

    for ( uint16_t i = 0; i < bufferSize; i++ )
    {
        NRF_LOG_INFO("pBuffer[%d] = %d", i, pBuffer[i]);
        // UART is spaming 0xFF so it has to be escaped
        if ( ( pBuffer[i] == START_BYTE ) ||
             ( pBuffer[i] == STOP_BYTE ) ||
             ( pBuffer[i] == ESCAPE_BYTE ) ||
             ( pBuffer[i] == 0xFF ) )
        {
            status = app_uart_put( ESCAPE_BYTE );
            if (status != NRF_SUCCESS)
            {
                NRF_LOG_INFO("Failure in %s() @line %d", __FUNCTION__, __LINE__);
                return status;
            }

            status = app_uart_put( escapeByte( pBuffer[i] ) );
            if (status != NRF_SUCCESS)
            {
                NRF_LOG_INFO("Failure in %s() @line %d", __FUNCTION__, __LINE__);
                return status;
            }
        }
        else
        {
            status = app_uart_put( pBuffer[i] );
            if (status != NRF_SUCCESS)
            {
                NRF_LOG_INFO("Failure in %s() @line %d", __FUNCTION__, __LINE__);
                return status;
            }
        }
    } // end of for-loop

    status = app_uart_put( STOP_BYTE );
    if (status != NRF_SUCCESS)
    {
        NRF_LOG_INFO("Failure in %s() @line %d", __FUNCTION__, __LINE__);
        return status;
    }

    return TRANSPORT_SUCCESS;
}

Am I using app_uart_put() incorrectly? Also, do functions like

nrf_pwr_mgmt_run()

 UART functionality?

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Thu, 02 Jun 2022 15:15:40 GMT

If the CLI UART backend is enabled, you will need to disable this or not start the CLI at all when using the UART instance for anything else. If you are using different UART instances (0 and 1) for the two libraries, you do not need to disable the CLI.

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Sami — Wed, 01 Jun 2022 18:57:44 GMT

Thank you for confirming...using CLI over UART was at the root of my problem. I'm now creating an instance of standard UART in order to send and receive byte-packed data structs. Do I need to stop my CLI process when using my standard instance of UART or can they co-exist together?

// Spawn an instance of UART
    static bool uart_instance_activated = false;

    if (!uart_instance_activated)
    {
        uart_instance_activated = true;
        uint32_t err_code = NRF_SUCCESS;
        const app_uart_comm_params_t comm_params =
        {
            UART_RX_PIN,
            UART_TX_PIN,
            UART_RTS_PIN_NUMBER,
            UART_CTS_PIN_NUMBER,
            UART_HWFC,
            false,
            NRF_UART_BAUDRATE_115200
        };

        APP_UART_FIFO_INIT(&comm_params,
                       UART_RX_BUF_SIZE,
                       UART_TX_BUF_SIZE,
                      uart_error_handle,
                APP_IRQ_PRIORITY_LOWEST,
                              err_code);

        APP_ERROR_CHECK(err_code);

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Wed, 01 Jun 2022 08:29:06 GMT

The CLI library uses strcmp() to check for matching commands. If the commands are not in string format (with a \0 string terminator), this will likely fail.

The UART peripheral/transport can support any byte-data, but you need to handle the received data correctly in the application.

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Sami — Tue, 31 May 2022 20:53:41 GMT

I think I see the issue here. I'm using a CLI over UART transport layer. Can CLU over UART support commands that are non-strings? For instance, byte-packed Structs as commands.

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Thu, 05 May 2022 13:21:59 GMT

Can you explain in more detail what you mean by "system simply gets lost and is unresponsive"? You should be able to see where the code is stuck with a debugger. If you can provide a minimal example and instructions to reproduce this behavior, we may be able to help debug it.

Do you have a softdevice enabled when doing the stepping through code? Stepping with the softdevice enabled will usually cause asserts, as the debugger blocks the softdevice to handle timing-critical interrupts/tasks.

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Sami — Wed, 04 May 2022 19:48:59 GMT

Retarget in sdk_config.h has been implemented and __getchar() is now compiling. However, I'm seeing this problem when I step through the code:

https://devzone.nordicsemi.com/f/nordic-q-a/44397/cannot-retarget-getchar-read-getch

This system simply gets lost and is unresponsive. Is there an inherit SDK bug or bug fix that is suggested?

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Tue, 03 May 2022 09:16:03 GMT

There is an implementation for __getChar() in the stdio retarget layer in the SDK (components\libraries\uart\retarget.c):

#elif defined(__GNUC__) && defined(__SES_ARM)

int __getchar(FILE * p_file)
{
    uint8_t input;
    while (app_uart_get(&input) == NRF_ERROR_NOT_FOUND)
    {
        // No implementation needed.
    }
    return input;
}

I'm assuming that the call to SEGGER_RTT_WaitKey() that you are seeing is from the SEGGER_RTT_Syscalls_SES.c file:

/********************************************************************* 
*
*       __getchar()
*
*  Function description
*    Wait for and get a character via RTT.
*/
int __getchar() {
  return SEGGER_RTT_WaitKey();
}

If you include and enable the UART retarget layer in your sdk_config.h file, the __getChar implementation in SEGGER_RTT_Syscalls_SES.c should be excluded by the "#if !defined(RETARGET_ENABLED) || RETARGET_ENABLED == 0"

// <q> RETARGET_ENABLED  - retarget - Retargeting stdio functions
 

#ifndef RETARGET_ENABLED
#define RETARGET_ENABLED 1
#endif

Best regards,
Jørgen

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Sami — Tue, 03 May 2022 07:39:08 GMT

I think I see the issue here. Viewing the call stack, my code eventually calls "getchar()", which calls:

__getChar();

which calls

SEGGER_RTT_WaitKey(); // here in lies the problem.

I'm trying to pull a byte from UART, and not RTT. Is there a way to retarget getChar() to pull a byte from UART? I'm using SES v5.68.

RE: How to Create an Instance of RPC (Remote Procedural Call) using the NRF52840

Jørgen Holmefjord — Fri, 29 Apr 2022 11:31:10 GMT

Hi,

As far as I know, we do not have any RPC libraries in nRF5 SDK. Have you added any libraries yourself, or where do you expect this support to come from?

If you can describe your use-case, requirements and setup in more details, we may be able to provide some suggestions.

We do have a RPC library in nRF Connect SDK, intended for the nRF5340, but this is not supported in the old nRF5 SDK.

Best regards,
Jørgen