Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
11 years, 9 months ago.
Serial, Interrups and the RTOS Library
I tried to get the serial port working by using the attach-function. I had some problems with that so I set up a little testprogram.
I use a serial bluetooth device connected to the mbed. This program resets the device and then shows the startupinformation which come from the device:
#include "mbed.h"
DigitalOut led1(LED1);
DigitalOut led2(LED2);
Serial pc(USBTX, USBRX);
DigitalOut rst(p28);
class btc {
public:
btc(PinName rx, PinName tx){
bt = new Serial(rx, tx);
bt->baud(38400);
bt->attach(this, &btc::callback);
}
void callback() {
led2 = !led2;
pc.printf("%c", bt->getc());
}
private:
Serial* bt;
};
int main() {
btc* mybt = new btc(p9, p10);
rst = 1;
wait(1);
rst = 0;
while (1) {
led1 = !led1;
wait(0.5);
}
}
That works fine. But at the moment I add the mbed RTOS Library to the projekt, the program freeze after first call of the interrupt-function. LED2 turns on, and then it freezes. I don't even have to include the rtos-header file. If I delete the RTOS Library, everything goes back to normal.
Anybody any ideas and/or solutions?
3 Answers
9 years, 11 months ago.
Hi Max and Emilio,
Not sure what the progress is, but I think at this point, we can get around by accessing UART TX and RX register directly instead of using putc() and getc().
The following link has a nice write up regarding how to directly access mbed hardware io.
http://developer.mbed.org/users/4180_1/notebook/cc-io-register-names/
I was able to get my code to work this way.
ZL
11 years, 9 months ago.
Hi Max, there are few implementation details that could not be obvious:
- when using the RTOS you cannot use mutexes in ISR.
printfuses mutexes for protecting the access tostdout- the
Serial attachcallback get executed in an ISR
We tried to document that in this paragraph of the RTOS documentation: RTOS::Mutex.
You should solve your problem removing the printf from your ISR: btc::callback.
HTH, Emilio
11 years, 9 months ago.
Hey Emilio,
thanks for your quick answer. I thougt about that too, so I just deleted line 18 and the same happens... Offcourse this way the interrups is never deleted but it should at least blink LED1...
To avoid the problem with blocking commands in ISR I usally start a new Thread, waiting for a signal and then doing the work I can't do in ISR. And the actual ISR only sends the signal to it. It works on InterruptIn for example. But doing that by using the attach function from Serial, I get siren lights, the moment it calls the set_signal-function of that Thread.
Edit: I actually only try to get an Interrup-driven serial ring buffer getting to work but running out of ideas...
nope, not working... It should anyway always come to the while-loop at the end of main, or not? Even I don't clear the interrupt?
posted by 08 Mar 2013Yes, i did that... It looks like this now
void callback() {
led2 = !led2;
bt->getc();
}
I changed the program now, so you can try out without any additional hardware...
#include "mbed.h"
DigitalOut led1(LED1);
DigitalOut led2(LED2);
Serial pc(USBTX, USBRX);
class pcc {
public:
pcc(){
pc.attach(this, &pcc::callback);
}
void callback() {
led2 = !led2;
pc.getc();
}
};
int main() {
pcc* mypcc = new pcc();
while (1) {
led1 = !led1;
wait(0.5);
}
}
At the beginning, LED1 is flashing, when I enter a character, it freezes...
posted by 08 Mar 2013OK, I tried with the simple and quick suggestions reading the code. I will open a ticket to run and debug the example, but it goes at the end of a long queue, do not expect a follow up soon.
posted by 08 Mar 2013Yes, all the serial stdio-like functions (printf, putc, getc, etc) end up calling actual stdio functions, that, like I said, are actually mutex protected: therefore they cannot be called from an ISR.
In a future revision of the mbed library integration with the RTOS we will try to improve this use case.
posted by 18 Jul 2013