Serial bug and firmware question

Firmware
1

Sorry for long post :smile:

I and Talybin are trying to identify a potential bug with Serial, first char in first message is always garbage. See Issue #682.

as example following code on Photon:

unsigned long lastTime = 0;

void setup()          
{
    Serial1.begin(9600);
}

void loop()  
{    
    unsigned long now = millis();     
    if (lastTime == 0 ||  ((now - lastTime) > 5000)){ 
        Serial1.println("!");
        lastTime = now; 
    }
}

give this output in Putty:

â–’!
!
!

We think reason is that there is copy paste error in firmware, there is no memset for tx_buffer, so that the reason for garbage char in first message.

So I trying to resolve it in firmware to see if it fixes this problem.

I install all depecies needed according too Particle.io firmware

after that i use

git clone https://github.com/spark/firmware.git
cd firmware
git checkout latest

Then open files in downloaded firmware and edit copypaste error from Issue #682 so we do memset both for rx and tx buffer.

hal/src/core/usart_hal.c#L120
hal/src/core/usart_hal.c#L215
hal/src/stm32f2xx/usart_hal.c#L148-L149
hal/src/stm32f2xx/usart_hal.c#L263-L264

Than I switch to modules folder, connect Photon in DFU-mode and run

make PLATFORM=photon clean all program-dfu

so photon receives changed fixed firmware. No errors received and firmware are loaded in photon.

Then under user/applications I create a folder test and create file test.cpp :

#include "application.h"

unsigned long lastTime = 0;

void setup()          
{
    Serial1.begin(9600);
}

void loop()  
{    
    unsigned long now = millis();     
    if (lastTime == 0 ||  ((now - lastTime) > 5000)){ 
        Serial1.println("!");
        lastTime = now; 
    }
}

Then i change to main folder and run

make PLATFORM=photon APP=test
make PLATFORM=photon APP=test program-dfu

In output i receive

!
!
!

but when i push reset i receive

â–’!
!
!
!

My question is, do I update photon firmware right or do i make mistake somewhere?

If I do correct firmware update, can it be somewhere else reason for garbage char is? Someone who can help us find it?

@changed blink to test

2

The steps you took seem good (apart from flashing blink after flashing your test app - I imagine that was a copy/paste error?)

I have seen this issue too. Is the garbage character always the same?

3

Yes :), no blink there, changed it.

Yes char is always the same.

4

Yes, the same char is suspesious. One theory is that compiler or OS fills the uninitialized memory with some char by default. I know Microsoft compiler/OS for example do fill with 0xCC.