Posted on February 25, 2014 at 16:45I found this problem when debug the CAN bus. The received data can not be showned in the printf via SWO. At first I thought there were something wrong in configuraion. But at last I found that the data can be shown in a LCD screen.
At last I located the problem at the blowing program.
int i = 0;
int flag = 0;
int t = 0;//
char buf[32];//buffer
while (1) {
if (i == 0) {
if (flag)//flag is non-zero means a message has been received.
sprintf(buf, ''%d\n'', t++);//write t to buf, and ++t.
else
sprintf(buf, ''a%d\n'', t++);//write t to buf. The 'a' is for distinguishing
LCD_Println(0, buf);//show the data in LCD screen
printf(buf);//send data to PC via SWO port
if(flag){//I didn't write this 3 lines at first, I'll explain this later.
while(1);
}
flag = 0;//clear the flag
i = 1000000;//it costs about 1s for i to decreased to zero
} else if (i > 0) {
i--;
}
if (CAN_GetFlagStatus(CANx, CAN_FLAG_FMP0)) {//data received
LED_Toggle(0);//toggle the led 0
flag = 1;
t = 0;//reset the variable t
CAN_Receive(CANx, CAN_FIFO0, &RxMessage);//receive the data, to clear the FLAG_FMP0
}
if (flag)//show the state of flag
LED_On(1);
else
LED_Off(1);
}
When there're no the line 13 to 15, the expected result is that when a message received, the printed number start again from zero. But the real result is that the number on the LCD do what expected, but the data received via SWO just increases, as if no data received by CAN bus.
After adding line 13 to 15, the expected result is that when a message received, the number is set to zero and stop increasing. The real result is that the number on the LCD do stop, but the number received from SWO port just increases as usual.
So It seems there are two core in the chip, and the one that manages the SWO port doesn't know that a message have been received from the CAN BUS.
I use a STM32F407VG, and the debugger is ST-Link on the STM32F4 Discovery board. The compiler I used is GCC.
