3 years, 1 month ago.

USBSerial and Serial interrupt


I have a problem with the following code. At first I used only serial interrupt and everything worked good. I put USBSerial interrupt to my code where the code waits to received character "1". The problem is that nothing works at the moment. Neither serial interrupt nor USB serial interrupt. I do not know where is a bug.

#include "mbed.h"
#include "USBSerial.h"
#include "MODSERIAL.h"
#include "at25sf041.h"
//#include "rtos.h"

DigitalOut LedStatus(P0_13);
DigitalOut LedBattery(P0_14);
DigitalOut USB_connect(P0_6);
AnalogIn ain(P0_11);

USBSerial usb(0x1f00, 0x2012, 0x0001, false);
DigitalIn Vbus(P0_3);
AT25SF041 memory(P0_9, P0_8, P0_10, P0_15);

MODSERIAL uart(P0_19, P0_18);
InterruptIn GPS_fix(P0_17);
volatile bool newline_detected = false;

char tmp;

void Rx_interrupt(MODSERIAL_IRQ_INFO *q)
    MODSERIAL *serial = q->serial;
    if ( serial->rxGetLastChar() == '\n') {
        newline_detected = true;
        LedBattery = !LedBattery;

void toogle()
    LedStatus = !LedStatus;

void usb_rx()
    LedStatus = !LedStatus;
    tmp = usb.getc();
    LedStatus = !LedStatus;

int main(){
    USB_connect = 0;
    uart.attach(&Rx_interrupt, MODSERIAL::RxIrq);

while (1)
  //  if (usb.readable())
     //   LedStatus = !LedStatus;
      //  tmp = usb.getc();
       // } 
 if (tmp == '1' && newline_detected) {
            newline_detected = false;
            char c;
            while((c = uart.getc()) != '\n') {
           //tmp = ' ';


1 Answer

2 years, 7 months ago.


I have similar problem with one of my projects. It seems that that mbed-rtos causes USBSerial.getc() to block in interrupts. With normal serial ports this can be resolved by accessing the serial registers directly inside the interrupt. With UsbSerial I don't know a proper solution yet.

USBSerial.getc() seems to start jamming in the interrupt after mbed-rtos is added to the project (even when rtos.h is not included).

If you're using mbed-rtos, I would recommend using the latest release of mbed, mbed OS, which includes mbed-rtos in the library. See Serial documentation here - https://docs.mbed.com/docs/mbed-os-api-reference/en/latest/APIs/interfaces/digital/Serial/

posted by Sarah Marsh 01 Sep 2017