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vvaltchev wrote:Just pick up an old Linux and try a two-way communication using minicom.

vvaltchev wrote:

nexos wrote:Anyway, @Bonfra, try testing the serial code in QEMU and see if anything gets sent to the serial monitor.

In my understanding, his code already works on QEMU. The problem is only with real hardware.

#define PORT 0x3f8          // COM1
 
static int init_serial() {
   outb(PORT + 1, 0x00);    // Disable all interrupts
   outb(PORT + 3, 0x80);    // Enable DLAB (set baud rate divisor)
   outb(PORT + 0, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
   outb(PORT + 1, 0x00);    //                  (hi byte)
   outb(PORT + 3, 0x03);    // 8 bits, no parity, one stop bit
   outb(PORT + 2, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
   outb(PORT + 4, 0x0B);    // IRQs enabled, RTS/DSR set
   outb(PORT + 4, 0x1E);    // Set in loopback mode, test the serial chip
   outb(PORT + 0, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)
 
   // Check if serial is faulty (i.e: not same byte as sent)
   if(inb(PORT + 0) != 0xAE) {
      return 1; // <---- here it returns error
   }
 
   // If serial is not faulty set it in normal operation mode
   // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
   outb(PORT + 4, 0x0F);
   return 0;
}

Bonfra wrote:Just tested, I didn't use minicom 'cause it's not installed on the Linux distro I used for testing and I don't want to search for a long enough ethernet cable but echo and cat works both ways so the cable and the configuration on the other side is perfect

Bonfra wrote:The problem must be in the initialization code, this one:

void init_serial_port(u16 port)
{
   outb(port + UART_IER, IER_NO_INTR);

   uart_set_divisor_latch(port, 1 /* 115200 baud */);

   outb(port + UART_LCR, LCR_8_BITS | LCR_1_STOP_BIT | LCR_NO_PARITY);

   outb(port + UART_FCR, FCR_ENABLE_FIFOs |
                         FCR_CLEAR_RECV_FIFO |
                         FCR_CLEAR_TR_FIFO |
                         FCR_INT_TRIG_LEVEL_3);

   outb(port + UART_MCR, MCR_DTR | MCR_RTS | MCR_AUX_OUTPUT_2);
   outb(port + UART_IER, IER_RCV_AVAIL_INTR);
}

vvaltchev wrote: Another random guess: have you tried just skipping that the lookback mode and its test and directly trying to send something to the other side?

Bonfra wrote:Yes: receiving data works, the problem is with sending data. I can use another pc to `echo "Hello There" > /dev/ttyUSB0` to the serial port and it's successfully received but when a response is sent back, nothing is caught by `cat /dev/ttyUSB0` (this exact procedure worked with the two machines running Linux).

bzt wrote:This could be an issue with the Linux device. Have you configured it properly using setserial?

bzt wrote: With FIFO for example it could be that the received bytes are sitting in the queue and not returned by the device. Or that the received bytes are sitting in the kernel buffer, and again, not returned by the device. With "echo" you have explicitly also sent a "\n" which might flush the buffer on the other side, but your code probably doesn't do that.

bzt wrote: I'd strongly recommend to install minicom, as others have already suggested. sudo apt-get install minicom or something. It should be a standard package, no trickery needed to install.

bzt wrote:Or you could also use my raspbootcom.c version, which compiles on a modern Linux without a fuzz and does all that termios setup I've mentioned. By default it prints all bytes it receives, and you don't have to worry about the other things it can do if you don't send 3 times Ctrl+C in a row.

bzt wrote: Finally about initialization, this code has been tested on real hardware and known to work, feel free to use it.