BUS FAULT when working with ASYNC UART

[backstreet.devisor]

Good Day.

When working with the UART in asynchronous mode, I occasionally get this error:

E: ***** BUS FAULT *****
E:   Precise data bus error
E:   BFAR Address: 0x20040000
E: r0/a1:  0x20000e90  r1/a2:  0x00000000  r2/a3:  0x0003f11e
E: r3/a4:  0x20000ee2 r12/ip:  0x20000380 r14/lr:  0x00000a51
E:  xpsr:  0x21000012
E: s[ 0]:  0x00008048  s[ 1]:  0x000125a4  s[ 2]:  0x00000000  s[ 3]:  0x00008048
E: s[ 4]:  0x40002000  s[ 5]:  0x00000000  s[ 6]:  0x20000118  s[ 7]:  0x00000a8f
E: s[ 8]:  0x00000a71  s[ 9]:  0x000073c9  s[10]:  0x20000ee2  s[11]:  0x00000005
E: s[12]:  0x00000000  s[13]:  0x00000000  s[14]:  0x00000000  s[15]:  0x00000000
E: fpscr:  0x00008048
E: Faulting instruction address (r15/pc): 0x000009e0
E: >>> ZEPHYR FATAL ERROR 25: Unknown error on CPU 0
E: Fault during interrupt handling

E: Current thread: 0x20000380 (unknown)
E: Resetting system<CR>*** Booting nRF Connect SDK v2.5.99-dev1 ***

Please tell me what this is related to and how to fix it.

Thank you.

[backstreet.devisor]

/* Receive buffer */
static uint8_t rx_buf[512] = {0};
/* Buffer for NMEA sentence*/
volatile static uint8_t sentence[82] = {0};

The algorithm of the program is as follows:

I receive data from GNSS until the buffer is completely filled. In the UART_RX_BUF_RELEASED event, I run the getStrFromRxBuffer() function which finds the $GNRMC string in the rx_buf receive buffer. Then I run the work to parsing the found string - k_work_submit 

case UART_RX_BUF_RELEASED:
	getStrFromRxBuffer();
	k_work_submit(&gnss_work);
	break;

Function getStrFromRxBuffer():

char * getStrFromRxBuffer(void){
	volatile bool waitingForStrBegin = true;
	volatile bool waitingReadySentence = false;
	volatile static int index = 0; /* index inside sentence buffer */
	volatile static int i = 0; /* index inside rx_buf */

while(!waitingReadySentence){

	while(waitingForStrBegin){
		if(rx_buf[i] == '$'){    // is line 65 in the original program code
			index = 0;
			sentence[index++] = rx_buf[i++];
			waitingForStrBegin = false;
		}
		else{
			i++;
		}
	}

	while(rx_buf[i] != '\n'){
		sentence[index++] = rx_buf[i++];
	}

	sentence[index] = '\0';

	const char * prefix = "$GNRMC";
	if(strncmp(sentence, prefix, strlen(prefix)) == 0){
		waitingReadySentence = true;
		return sentence;
		}
		else {
		memset(sentence, 0, sizeof(sentence));
		index = 0;
		waitingForStrBegin = true;
		}
	}
}

Inside the work function, I clear the sentence and rx_buf buffers and then turn on the UART receiver and everything repeats again.

static void gnss_work_cb (struct k_work *work){

struct minmea_sentence_rmc frame;
if(minmea_parse_rmc(&frame, sentence)){
                LOG_DBG("\n Latitude: %f\n Longitude: %f\n Speed: %f\n",
                        minmea_tocoord(&frame.latitude),
                        minmea_tocoord(&frame.longitude),
                        minmea_tofloat(&frame.speed));
            }
            else {
                 LOG_DBG(INDENT_SPACES "$GNRMC sentence is not parsed\n");
            }
	memset(sentence, 0, sizeof(sentence));
	memset(rx_buf, 0, sizeof(rx_buf));
	uart_rx_enable(uart, rx_buf, sizeof(rx_buf), RECEIVE_TIMEOUT);
}

[Vidar Berg]

Thanks for the additional information. I don't see anything that would prevent 'rx_buf' from overrunning in cases where the '$' might not be found. The 'i' index will just keep incrementing until it triggers a fault.

[backstreet.devisor]

Yes, the error was related to the "i" index. I could not determine the cause of the error on my own.

Thank you very much for your help!