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5 years, 7 months ago.
Access to stdin/stdout Serial object
Hello,
I have defined TX/RX pins in mbed_app.json so stdin/stdout are mapped to it and I can use printf()/getchar() and such to access it.
I'd like to use the Serial.attach() method to detect communication with the board but I can't find the Serial object it is linked to.
Right now I defined a RawSerial object with the same pins and can use attach() on it. It's working, but I'm not sure it's the best thing to do, resource-wise.
Is there a better way to access the console as a Serial or RawSerial object?
Thanks!
1 Answer
5 years, 7 months ago.
Hello Matthieu,
You can try to override the default console as below.
#include "mbed.h"
DigitalOut led1(LED1);
RawSerial* mySerial;
void onSerialReceived()
{
char c = mySerial->getc();
if (c == 't')
led1 = !led1;
}
FileHandle* mbed::mbed_override_console(int)
{
static UARTSerial myConsole(PA_9, PA_10, 9600);
mySerial = reinterpret_cast<RawSerial*>(&myConsole);
mySerial->attach(onSerialReceived);
return &myConsole;
}
int main()
{
while (true) {
printf("blink\r\n");
wait(0.5);
}
}
Thanks Zoltan! Just to be sure: the ISR is the onSerialReceived() function in that case?
I think I felt the problem you're referring to because I'm trying to "reply" to the serial command within that function, which lead to a 0x80020115 error; but I'll ask a separate question for that.
Yes, onSerialReceived is the ISR in the code above. Sorry, I modified (simplified) my answer in the meantime because if you use RawSerial instead of Serial you can call getc/putc in the ISR without having a system fault. So a code like below should work:
#include "mbed.h"
DigitalOut led1(LED1);
RawSerial* mySerial;
void onSerialReceived()
{
mySerial->putc(mySerial->getc());
}
FileHandle* mbed::mbed_override_console(int)
{
static UARTSerial myConsole(PA_9, PA_10, 9600);
mySerial = reinterpret_cast<RawSerial*>(&myConsole);
mySerial->attach(onSerialReceived);
return &myConsole;
}
int main()
{
while (true) {
led1 = !led1;
printf("blink\r\n");
wait(0.5);
}
}
Looks promising, I'll try to test it asap. One last thing: is it ok to cast RawSerial* to FileHandle*? I don't see it anywhere in the RawSerial hierarchy... I guess it could work thanks to the virtual methods? (my C++ is sooo rusty...).
Down-cast isn't always safe. But in this case it seems OK. To achieve safe down-cast you can use dynamic_cast and then test the returned pointer against NULL rather than to use reinterpret_cast or static_cast . But it requires a little bit of extra overhead to run.
Working great! In my case getc()/putc() is all I need but I'll probably ask "why" on a more generalist programming Q&A site like StackOverflow.
Thanks again Zoltan!