It takes up to 40 min before a packet is lost, (at rate of 1 packet every few minutes),
The MCU use Linux kernel 3.18.48,
Using Scope, (on UART's Rx Pin), I can see the packets, (about 15 bytes long), are sent well.
But the read() doesn't return, with any of the packet's bytes,
(VMIN = 1, VTIME = 0, configured to return if at least 1 byte is in the Rx buffer),
This code is used in 4 other projects, with different HW Board, and we never saw this issue before.
Can you share ideas of how to tackle such issue? How can I debug the UART driver?
To better understand where the packet got lost,
Thanks,
Logic Analyzer of the Lost Packet
E_UARTDRV_STATUS UartDrv_Open(void *pUart, S_UartDrv_InitData *init_data)
{
struct termios tty;
struct serial_struct serial;
/*
* O_RDWR - Opens the port for reading and writing
* O_NOCTTY - The port never becomes the controlling terminal of the process.
* O_NDELAY - Use non-blocking I/O.
* On some systems this also means the RS232 DCD signal line is ignored.
* Note well: if present, the O_EXCL flag is silently ignored by the kernel when opening a serial device like a modem.
* On modern Linux systems programs like ModemManager will sometimes read and write to your device and possibly corrupt your program state.
* To avoid problems with programs like ModemManager you should set TIOCEXCL on the terminal after associating a terminal with the device.
* You cannot open with O_EXCL because it is silently ignored.
*/
fd = open(init_data->PortName, O_RDWR | O_NOCTTY | O_NDELAY);
if (fd == -1) // if there is an invalid descriptor, print the reason {
SYS_LOG_ERR_V("fd invalid whilst trying to open com port %s: %s\n", init_data->PortName, strerror(errno));
return UARTDRV_STATUS_ERROR;
}
if (tcflush(fd, TCIOFLUSH) < 0) {
SYS_LOG_ERR_V("Error failed to flush input output buffers %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
// Enable low latency...this should affect the file /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
if (ioctl(fd, TIOCGSERIAL, &serial) < 0) {
SYS_LOG_ERR_V("Error failed to get latency current value: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
serial.flags |= ASYNC_LOW_LATENCY;
if (ioctl(fd, TIOCSSERIAL, &serial) < 0) {
SYS_LOG_ERR_V("Error failed to set Low latency: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
if (fcntl(fd, F_SETFL, 0) < 0) {
SYS_LOG_ERR_V("Error failed to set file flags: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
/* Get current configuration */
if (tcgetattr(fd, &tty) < 0) {
SYS_LOG_ERR_V("Error failed to get current configuration: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
if (cfsetospeed(&tty, init_data->baud) < 0) {
SYS_LOG_ERR_V("Error failed to set output baud rate: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
if (cfsetispeed(&tty, init_data->baud) < 0) {
SYS_LOG_ERR_V("Error failed to set input baud rate: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
tty.c_cflag |= (CLOCAL | CREAD); /* Enable the receiver and set local mode */
tty.c_cflag &= ~CSIZE;
tty.c_cflag |= CS8; /* 8-bit characters */
tty.c_cflag &= ~PARENB; /* no parity bit */
tty.c_cflag &= ~CSTOPB; /* only need 1 stop bit */
/*
* Input flags - Turn off input processing
* convert break to null byte, no CR to NL translation,
* no NL to CR translation, don't mark parity errors or breaks
* no input parity check, don't strip high bit off,
* no XON/XOFF software flow control
* BRKINT - If this bit is set and IGNBRK is not set, a break condition clears the terminal input and output queues and raises a SIGINT signal for the foreground process group associated with the terminal.
* If neither BRKINT nor IGNBRK are set, a break condition is passed to the application as a single '\0' character if PARMRK is not set, or otherwise as a three-character sequence '\377', '\0', '\0'.
* INPCK - If this bit is set, input parity checking is enabled. If it is not set, no checking at all is done for parity errors on input; the characters are simply passed through to the application.
* Parity checking on input processing is independent of whether parity detection and generation on the underlying terminal hardware is enabled; see Control Modes.
* For example, you could clear the INPCK input mode flag and set the PARENB control mode flag to ignore parity errors on input, but still generate parity on output.
* If this bit is set, what happens when a parity error is detected depends on whether the IGNPAR or PARMRK bits are set. If neither of these bits are set, a byte with a parity error is passed to the application as a '\0' character.
*/
tty.c_iflag &= ~(BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
/*
* IGNBRK - If this bit is set, break conditions are ignored.
* A break condition is defined in the context of asynchronous serial data transmission as a series of zero-value bits longer than a single byte.
*/
tty.c_iflag |= IGNBRK;
/*
* No line processing
* echo off, echo newline off, canonical mode off,
* extended input processing off, signal chars off
*/
tty.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
/*
* Output flags - Turn off output processing
* no CR to NL translation, no NL to CR-NL translation,
* no NL to CR translation, no column 0 CR suppression,
* no Ctrl-D suppression, no fill characters, no case mapping,
* no local output processing
*
* c_oflag &= ~(OCRNL | ONLCR | ONLRET | ONOCR | ONOEOT| OFILL | OLCUC | OPOST);
*/
tty.c_oflag = 0;
/* fetch bytes as they become available */
tty.c_cc[VMIN] = 0;
tty.c_cc[VTIME] = 1; // timeout in 10th of second
if (tcsetattr(fd, TCSANOW, &tty) != 0) {
SYS_LOG_ERR_V("Error failed to set new configuration: %s\n", strerror(errno));
return UARTDRV_STATUS_ERROR;
}
uartPeripheral.fd = fd;
return UARTDRV_STATUS_SUCCESS;
}
uint8_t *UartDrv_Rx(S_UartDrv_Handle *handle, uint16_t bytesToRead, uint16_t *numBytesRead)
{
ssize_t n_read;
uint16_t n_TotalReadBytes = 0;
struct timespec timestamp;
struct timespec now;
long diff_ms;
bool Timeout = false, isPartialRead = false;
if (handle == NULL) {
SYS_LOG_ERR("UartDrv Error: async rx error - peripheral error");
exit(EXIT_FAILURE);
}
if (bytesToRead > sizeof(uartPeripheral.buffer_rx)) {
ESILOG_ERR_V("Param Error: Invalid length %u, max length %zu", bytesToRead, sizeof(uartPeripheral.buffer_rx));
*numBytesRead = 0;
return NULL;
}
while(n_TotalReadBytes < bytesToRead && !Timeout) {
do {
n_read = read(uartPeripheral.fd, &uartPeripheral.buffer_rx[n_TotalReadBytes], bytesToRead - n_TotalReadBytes);
if (isPartialRead) {
clock_gettime(CLOCK_REALTIME, &now);
diff_ms = (now.tv_sec - timestamp.tv_sec)*1000;
diff_ms += (now.tv_nsec - timestamp.tv_nsec)/1000000;
if (diff_ms > UART_READ_TIMEOUT_MS) {
SYS_LOG_ERR("UartDrv_Rx: Error, timeout while reading\r\n");
Timeout = true;
}
}
} while ((n_read != -1) && (n_read == 0) && !Timeout);
if (n_read == -1) {
if (errno == EINTR) {
ESILOG_WARN("Uart Interrupted");
continue;
}
ESILOG_ERR_V("Uart Error: [%d, %s]", errno, strerror(errno));
exit(EXIT_FAILURE);
}
n_TotalReadBytes += (uint16_t)n_read;
if (n_TotalReadBytes < bytesToRead) {
//SYS_LOG_DBG_V("UartDrv_Rx: couldn't fetch all bytes, read %hu, expected %hu, continue reading %s\r\n", n_TotalReadBytes, bytesToRead, isPartialRead? "During Partial read": "");
if (!isPartialRead) {
isPartialRead = true;
clock_gettime(CLOCK_REALTIME, ×tamp);
}
}
}
*numBytesRead = n_TotalReadBytes;
return uartPeripheral.buffer_rx;
}
