How to disable framing errors in serial_lte_modem

RE: How to disable framing errors in serial_lte_modem

Håkon Alseth — Fri, 31 Jul 2020 12:27:31 GMT

Hi,

[quote user="KeithC"]I figure Nordic may correct this in a future release, as I saw another question within the past week where this was mentioned (I can't find it now), and that this is a known issue. [/quote]

Yes, you're right! Thank you for investigating. I will add a link to your thread in the already made internal bug report.

Kind regards,

Håkon

RE: How to disable framing errors in serial_lte_modem

Caycee — Thu, 30 Jul 2020 13:38:52 GMT

I'm using CR_MODE. I didn't bother with the other modes for the time being.

I inserted that in cmd_send just prior to at_cmd_write. It fixed the issue I was having when just a single '\r' being received caused an ignore-everything-else mode.

I figure Nordic may correct this in a future release, as I saw another question within the past week where this was mentioned (I can't find it now), and that this is a known issue.

RE: How to disable framing errors in serial_lte_modem

Håkon Alseth — Thu, 30 Jul 2020 09:12:25 GMT

Hi,

[quote user="KeithC"]I still ought to be able to clear the error from user application and reset things so further communications are possible. Is there such a command in the API or is that all in the protected/secure area?[/quote]

The driver should clear it for you when an error event is set: https://github.com/nrfconnect/sdk-zephyr/blob/v2.3.0-rc1-ncs1/drivers/serial/uart_nrfx_uarte.c#L721

This function call essentially reads the NRF_UARTEx->ERRORSRC register, and writes '1' to the bits that are set (which clears the source)

[quote user="KeithC"]I also had to include the following code in cmd_send in slm_at_host.c to assure blank lines would not stop up the modem...though I'm not sure this is the best way to handle it.[/quote]

You insert this logic in slm_at_host.c::cmd_send()? Which termination mode are you currently using? Does procedure lock up the device?

Kind regards,

Håkon

RE: How to disable framing errors in serial_lte_modem

Caycee — Wed, 29 Jul 2020 17:02:27 GMT

Okay, that change does allow the modem to resume (often with an error on the next command).

I still ought to be able to clear the error from user application and reset things so further communications are possible. Is there such a command in the API or is that all in the protected/secure area?

I also had to include the following code in cmd_send in slm_at_host.c to assure blank lines would not stop up the modem...though I'm not sure this is the best way to handle it.

    if ((strlen(at_buf) == 1) && (at_buf[0] == '\r')) 
    {
        LOG_WRN("CR_only");
        at_buf[0] = 0;
        goto done;
    }

RE: How to disable framing errors in serial_lte_modem

Håkon Alseth — Wed, 29 Jul 2020 12:40:32 GMT

Hi,

It looks like you have stumbled upon a bug on our side! My apologies for the inconvenience!

When a framing error occurs, this sequence will be called:

https://github.com/nrfconnect/sdk-zephyr/blob/master/drivers/serial/uart_nrfx_uarte.c#L732-L733

However; the RX isn't actually stopped when the callback is sent, but rather afterwards, which makes it quite hard for the application to recover. I'll make an internal ticket on this, and propose that we do not stop the RX in uart_nrfx_uarte.c, or change the order of the user-callback and the stopping of the UARTE RX, so that the application can start it again by calling uart_rx_enable(...) from the user-callback.

As I see it, you have two options here to work around the issue:

1. Comment out the call to (void) uarte_nrfx_rx_disable(dev);

2. Change the ordering of the above linked two lines, and call uart_rx_enable() in your application.

Kind regards,

Håkon