BluePill Serial communication problem (data not received)

[jawa.bukowicz]

Hi everyone!
I’m trying to use BluePill to communicate over built-in USB using Serial mode - and cannot get 2-way communication working…

Data from BluePill → desktop is transmitted, but nothing is received.
Tried another board - same result
If I use some sample program in Cube32IDE - both receiving and transmitting works, so that’s not a hardware issue.

here’s my environment:

[env:genericSTM32F103C8]
platform = ststm32
board = genericSTM32F103C8
framework = arduino
lib_deps = thijse/CmdMessenger@^4.1.0
monitor_speed = 9600
upload_protocol = stlink
upload_flags = -c set CPUTAPID 0x2ba01477
build_flags = 
    -D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC
    -D USBCON
    -D USBD_USE_CDC
    -D ENABLE_USB_SERIAL
    -D USB_MANUFACTURER="UnknownMFG"
    -D USB_PRODUCT="BluePill"
    -D USBD_VID=0x0483
    -D USBD_PID=0x5740
    -D HAL_PCD_MODULE_ENABLED     
;monitor_dtr = 0
debug_tool = stlink

and here’s the code itself:

#include <Arduino.h>
const uint8_t kbStdLed = PC13;        // Pin of Built-in LED
unsigned long lastTransmission;

void setup()
{
    Serial.begin(9600);
    while (!Serial);
    pinMode(kbStdLed, OUTPUT);
}
void loop()
{
    uint8_t incomingByte;
    if ((millis() - lastTransmission) >= 2000)
    {
        Serial.println("Bbbnbnbas");   //<- this works
        lastTransmission = millis();
    }
    if (Serial.available() > 0)
    {
        digitalWrite(kbStdLed, digitalRead(kbStdLed) ^ 1);    //<- this doesn't work
        incomingByte = Serial.available();  
        Serial.print("I received: ");                 //<- this doesn't work
        Serial.println(incomingByte, DEC);   //<- this doesn't work
    }
}

Upon uploading the code, LED is off

After I connect via terminal program, it goes on - and stays on even if I send something

[maxgerhardt]

@jawa.bukowicz

        incomingByte = Serial.available();  
        Serial.print("I received: ");                 //<- this doesn't work
        Serial.println(incomingByte, DEC);   //<- this doesn't work

Serial.available() returns the number of bytes available to read.

Serial.read() reads an available byte, or returns -1 of none can be read.

Since in this case, you have already guarded executed with if(Serial.available() > 0), you can just

        incomingByte = (char) Serial.read();
        Serial.print("I received: ");
        Serial.println(incomingByte);

You might also have to assert DTR = 1 in the platformio.ini, it it might ignore all input.

[jawa.bukowicz]

@maxgerhardt

You might also have to assert DTR = 1 in the platformio.ini, it it might ignore all input.

can you clarify please?
I tried like that:
-D DTR=1 in Build Flags - no changes

if I add to environment section - there’s a warning:
Warning! Ignore unknown configuration option dtr in section [env:genericSTM32F103C8]

[jawa.bukowicz]

@maxgerhardt

Serial.available() returns the number of bytes available to read.

Correct, I was trying to get at least some feedback (number of bytes sent in this case) - but no luck so far

First line (LED changing status) is to indicate if “IF” statement being fired - which apparently didn’t

Serial.println("Bbbnbnbas");   //<- this works

Serial.print("I received: ");                 //<- this doesn't work

[maxgerhardt]

@jawa.bukowicz

;monitor_dtr = 0

You already have the DTR I meant, just commented out. Comment it in, and try 0 as well as 1.

@jawa.bukowicz

Serial.println("Bbbnbnbas");   //<- this works

Serial.print("I received: "); //<- this doesn't work

Then Serial.flush();

[jawa.bukowicz]

@maxgerhardt

Then Serial.flush();

didn’t help

tried a) after printing something
b) before checking if any incoming bytes available

[jawa.bukowicz]

@maxgerhardt

Comment it in, and try 0 as well as 1.

no apparent changes…

• when I check “DTR” in my terminal program - transmission starts (“Bbbnbnbas”),
• when uncheck - stops
  but incoming data is not read in both cases

I also noticed something strange: if I try to send something, this output “freezes” for ~2 seconds and then prints out 3 lines at once

Serial.println("Bbbnbnbas");

[maxgerhardt]

This is working just fine-

[env:genericSTM32F103C8]
platform = ststm32
board = genericSTM32F103C8
framework = arduino
build_flags = 
    -D PIO_FRAMEWORK_ARDUINO_ENABLE_CDC
    -D USBCON
    -D USBD_USE_CDC
    -D ENABLE_USB_SERIAL
    '-D USB_MANUFACTURER="UnknownMFG"'
    '-D USB_PRODUCT="BluePill"'
    -D USBD_VID=0x0483
    -D USBD_PID=0x5740
    -D HAL_PCD_MODULE_ENABLED
upload_protocol = cmsis-dap
monitor_dtr = 1

#include <Arduino.h>
const uint8_t kbStdLed = PC13;        // Pin of Built-in LED
unsigned long lastTransmission;

void setup()
{
    Serial.begin(9600);
    while (!Serial);
    pinMode(kbStdLed, OUTPUT);
}
void loop()
{
    char incomingByte;
    if ((millis() - lastTransmission) >= 2000)
    {
        Serial.println("Bbbnbnbas");   //<- this works
        lastTransmission = millis();
    }
    if (Serial.available() > 0)
    {
        digitalWrite(kbStdLed, digitalRead(kbStdLed) ^ 1);    //<- this doesn't work
        incomingByte = (char) Serial.read();
        Serial.print("I received: ");
        Serial.println(incomingByte);
    }
}

Same in hterm

[jawa.bukowicz]

Thanks a lot for checking!
It looks like I’m out of luck with those clone boards then…

How did you manage to find original one?

[jawa.bukowicz]

I remember someone mentioning “wrong USB pullup resistor” during my searches - could this be the case here?

Can you make anything out of this picture?
R10 is 1.5K - looks correct
R9/R11 are 22 Ohm - close enough as well

[jawa.bukowicz]

[maxgerhardt]

@jawa.bukowicz

If you can get the board to be recognized via USB and send this data, then there is no problem with the USB pullup resistors.