Implement flashlog backend

RE: Implement flashlog backend

gilbertjuly — Fri, 11 Jun 2021 11:09:40 GMT

Thank you, Vidar, that's helpful.

RE: Implement flashlog backend

Vidar Berg — Fri, 11 Jun 2021 08:39:14 GMT

The log entry stored at address 0x52000 is referencing a text string stored at 0x0004e41c in this case. Remember that you can have multiple log entries referencing the same text string. This makes it so that you don't have to write the same text string over and over again in flash.

As an example, lets say you have periodic logging of some sensor value and the data is logged with this line of code:

NRF_LOG_INFO( "sensor value :%d", sensor_value)

Here the string "sensor value :" will be stored at some other location in flash and only referenced with a pointer from the log entry. the sensor value argument will be stored each time with the log data, because it isn't a constant value.

RE: Implement flashlog backend

gilbertjuly — Fri, 11 Jun 2021 02:19:22 GMT

Vidar, I don't understand... from the picture, the address to where log is stored is 0x0004e41c, how come 0x52000 is the log entry? Could you please explain more? Thank you.

RE: Implement flashlog backend

Vidar Berg — Tue, 25 Feb 2020 13:32:55 GMT

NRF_LOG_FLUSH() may cause the program to hang if called from an interrupt context as the asynchronous logger backends rely on various interrupts to come through to signal completion of a transfer (e.g., Softdevice use interrupt to notify the result of a flash operation to the app). Could that explain what happens here, or does the program appear to continue after the log flush? Also, have you tried to not start advertising/scanning in case BLE activity is interfering with the flash operations (flash scheduling with Softdevice)?

I have tried to replicate this here as well. I took the ble_app_hrs from SDK 16.0.0 and added the code you posted here. It's attached below if you wish to compare it against yours.

devzone.nordicsemi.com/.../ble_5F00_app_5F00_hrs_5F00_w_5F00_flashlog.zip

RE: Implement flashlog backend

corentind — Mon, 24 Feb 2020 23:06:39 GMT

Thank you.

I added some logging to the nrf_fstorage_write(). It looks like it gets called the first time I do an NRF_LOG_FLUSH() but not after. If I try to read the flash I still get "Flash end reached".

RE: Implement flashlog backend

Vidar Berg — Mon, 24 Feb 2020 10:17:28 GMT

The flash log area starts directly after the application (ie first page aligned address) when NRF_LOG_BACKEND_FLASH_START_PAGE==0. But you can specify any fixed page address for NRF_LOG_BACKEND_FLASH_START_PAGE as long as it doesn't overlap with something else.

Are you able to debug the code and check if nrf_fstorage_write() calls are being made in the nrf_log_backend_flash.c?

RE: Implement flashlog backend

corentind — Sat, 22 Feb 2020 00:40:51 GMT

Thanks for the clarification regarding the format.

I see the firmware including the strings being stored in the flash but I don't think the logs are here.

I have been using the following function to test the flash:

void test_flashlog()
{

    // Test log reader
    ret_code_t error_code;
    uint32_t token = 0;
    nrf_log_header_t * p_header = NULL;
    uint8_t * p_data = NULL;
    NRF_LOG_INFO("Reading flash");

    while(true)
    {
        error_code = nrf_log_backend_flash_next_entry_get(&token, &p_header, &p_data);
        if(error_code != NRF_SUCCESS)
        {
            if(error_code == NRF_ERROR_NOT_FOUND)
            {
                NRF_LOG_INFO("Flash end reached");
            }
            else
            {
                NRF_LOG_WARNING("Read flash error code %d", error_code);
        }
        break;
        }
        else
        {
            NRF_LOG_INFO("Location %d", token);
            NRF_LOG_INFO("Read Data: %s", p_data);
            log_entry_process(p_header, p_data);
        }
    }
}

It returns that the flash end was reached straightaway as if it was empty.

I have a question -- Is the address where the logs are stored always at 0x52000? If not how to determine the address?

RE: Implement flashlog backend

Vidar Berg — Fri, 21 Feb 2020 09:39:13 GMT

Hi,

Do you see anything stored in this flash page? The format of the log data might be different from what you expect - instead of storing log messages in cleartext we store it as serialized logger objects with pointers referencing hardcoded messages inside the application image itself. This is to avoid duplication of log messages in flash.