Slow serial baudrates cause exceptions / WDT

[HakamSaffour]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [framework-arduinoespressif8266 2.7.4]
• Development Env: [Platformio]
• Operating System: [Windows]

Settings in IDE

• Module: [WeMos D1 R2 and mini]
• Flash Mode: [dio]
• Flash Size: [4MB]
• lwip Variant: [v1.4|v2 Lower Memory|Higher Bandwidth]
• Reset Method: [clk]
• Flash Frequency: [40Mhz]
• CPU Frequency: [80Mhz]
• Upload Using: [SERIAL]
• Upload Speed: [115200] (serial upload only)
• PlatformIO - ini file:

[env:d1_mini]
platform = espressif8266
board = d1_mini
framework = arduino
board_build.filesystem = littlefs

; COM1 or COM3
upload_port = COM[4]
upload_speed = 115200

monitor_port = COM[4]
monitor_speed = 115200
monitor_flags=
    --parity
    N

Problem Description

I want to use LittleFS to save some data coming from serial port at baudrate 110, N81
I tested the provided example in:
https://github.com/esp8266/Arduino/tree/master/libraries/LittleFS/examples/LittleFS_Timestamp
and it works fine at baudrate 115200
but when changing baudrate to 110, the code seems to retart (exception)

I need to have a running FS at baudrate of 110, because I can not change the baudrate of the device I am connected to.

Sketch

https://github.com/esp8266/Arduino/blob/master/libraries/LittleFS/examples/LittleFS_Timestamp/LittleFS_Timestamp.ino

Debug Messages

@ Baudrate 110

@baudrate 115200

[devyte]

Note: probably yield() needed in this while:

Arduino/cores/esp8266/uart.cpp

Line 477 in 8b662ed

while(uart_tx_fifo_full(uart_nr));

[devyte]

or this one (might be lighter):

Arduino/cores/esp8266/uart.cpp

Line 509 in 8b662ed

while (size--)

[earlephilhower]

Adding yield()s in the UART code needs to be careful about IRQ and SYS context safety. I believe both can perform UART writes.

[HakamSaffour]

@devyte
so you mean it is related to uart code?
why then the code restart at:

if(!LittleFS.begin())

[d-a-v]

@HakamSaffour
110 bauds is 11 printed chars per second.
yield() or loop() calling frequency must be much more higher than once per second.
You may try and add a call to yield() after every Serial.print.
Or you may try and use an alternative print function:

void myPrint (const String& toPrint) {
    for (int i = 0; i < toPrint.length(); i++) {
        Serial.print(toPrint[i]);
        yield();
    }
}

...
    myPrint("I hope this works better\n"); // Serial.println("I hope this works");

[HakamSaffour]

@HakamSaffour
110 bauds is 11 printed chars per second.
yield() or loop() calling frequency must be much more higher than once per second.
You may try and add a call to yield() after every Serial.print.
Or you may try and use an alternative print function:

void myPrint (const String& toPrint) {
    for (int i = 0; i < toPrint.length(); i++) {
        Serial.print(toPrint[i]);
        yield();
    }
}

...
    myPrint("I hope this works better\n"); // Serial.println("I hope this works");

it seems to be working (using the alternative print function), no crash any more.
But I need to write a wrapper for each print type, ex: Print, PrintIn, print(int, etc.)

[d-a-v]

But I need to write a wrapper for each print type, ex: Print, PrintIn, print(int, etc.)

True.

Would it be wise to do that in

Arduino/cores/esp8266/uart.cpp

Line 509 in 8b662ed

while (size--)

    while (size--)
        uart_do_write_char(uart_nr, pgm_read_byte(buf++));

=>

    if (can_yield() && 100*size/(baud/10) > 0) {
        // it takes more than 0.01s to print this string => yielding between chars
        // ( <=> (1000*size)/baud>0 <~> (size<<10)/baud > 0 )
        while (size--) {
            uart_do_write_char(uart_nr, pgm_read_byte(buf++));
            yield();
        }
    } else {
        while (size--) {
            uart_do_write_char(uart_nr, pgm_read_byte(buf++));
        }
    }

[HakamSaffour]

I replaced 'baud' with 'baud_rate' but I did not find 'can_yield', any hint?

if (can_yield() && 100*size/(uart->baud_rate/10) > 0) {

[d-a-v]

any hint?

In coredecls.h, sorry for the lack of clarity

[HakamSaffour]

Hello @d-a-v

Thank you for your solution.

I made the modifications in uart.cpp - as mentioned by you - and I tried this code

Sketch

https://github.com/esp8266/Arduino/blob/master/libraries/LittleFS/examples/LittleFS_Timestamp/LittleFS_Timestamp.ino

and it looks to be working without any problem at baudrate = 110 and also at baud rate = 115200

shall I make a merge request to uart.cpp ?

[earlephilhower]

@HakamSaffour sure, please throw a PR our way. I'm not sure the exact changes, but this might also fix a problem w/MDNS debugging at 9600 baud (another issue open to document it) where I think it has the same overflow due to its chattiness.

[Tech-TX]

Wow... welcome to the 1970s! I haven't seen 110baud since I used an ASR33 Teletype over an acoustic-coupled modem time-sharing on an old Sperry Univac 9000 computer.

Two tin cans and a piece of string is a more efficient method of data transfer... no wonder the issue never came up until now.

[TD-er]

Last week I had an user report WDT crashes when running software serial at 1200 baud.
Maybe also add some similar fix there?

[d-a-v]

Maybe also add some similar fix there?

cc @dok-net

[HakamSaffour]

A PR is created.

[dok-net]

@d-a-v I've provided a ready-to-merge PR #7799 to fix this. It should call yield() at a usefully lower frequency in those cases where not only the low bitrate, but a large buffer is the culprit that's causing a long interval without wdt resets before. Please check it off if you agree.