Zerocat Chipflasher  v0.4.10-182-333b622f
Flash free firmware to BIOS chips, kick the Management Engine.
Serial Howto
Fix missing copyright and license infos in subsections!

How to setup a Serial Connection

Sample code was used to start building connect. The sample code had been picked from Serial_Programming.pdf, found at Wikipedia.

Then, we learned how to control the DTR-line, which is used to reset the Propeller. Again, sample code helped us, found at the Linux Programmer's Manual, i.e.:

  • $ man tty_ioctl, section 'modem control' and section 'EXAMPLE'.
  • $ man termios

More Places of Information

Infos by Copy&Paste

From <tt>$ man tty_ioctl</tt>...


//Check the condition of DTR on the serial port.

#include <termios.h>
#include <fcntl.h>
#include <sys/ioctl.h>

int main(void)
    int fd, serial;

    fd = open("/dev/ttyS0", O_RDONLY);
    ioctl(fd, TIOCMGET, &serial);
    if (serial & TIOCM_DTR)
        puts("TIOCM_DTR is not set");
        puts("TIOCM_DTR is set");

From <tt>Serial_Programming.pdf</tt>...

Cutout 1:

5.1.5 termios

A simple terminal program with termios.h can look like this:

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>

int main(int argc, char ** argv)
  struct termios tio;
  struct termios stdio;
  struct termios old_stdio;
  int tty_fd;
  unsigned char c = 'D';

  tcgetattr(STDOUT_FILENO, &old_stdio);
  printf("Please start with %s /dev/ttyS0\n", argv[0]);

  memset(&stdio, 0, sizeof(stdio));
  stdio.c_iflag = 0;
  stdio.c_oflag = 0;
  stdio.c_cflag = 0;
  stdio.c_lflag = 0;
  stdio.c_cc[VMIN] = 1;
  stdio.c_cc[VTIME] = 0;
  tcsetattr(STDOUT_FILENO, TCSANOW, &stdio);
  tcsetattr(STDOUT_FILENO, TCSAFLUSH, &stdio);
  // make the reads non-blocking

  memset(&tio, 0, sizeof(tio));
  tio.c_iflag = 0;
  tio.c_oflag = 0;
  tio.c_cflag = CS8|CREAD|CLOCAL;
  // 8n1, see termios.h for more information

  tio.c_lflag = 0;
  tio.c_cc[VMIN] = 1;
  tio.c_cc[VTIME] = 5;
  tty_fd=open(argv[1], O_RDWR | O_NONBLOCK);
  cfsetospeed(&tio, B115200);  // 115200 baud
  cfsetispeed(&tio, B115200);  // 115200 baud
  tcsetattr(tty_fd, TCSANOW, &tio);
  while (c != 'q')
    if (read(tty_fd, &c, 1) > 0) write(STDOUT_FILENO, &c, 1);
    // if new data is available on the serial port, print it out

    if (read(STDIN_FILENO, &c, 1) > 0) write(tty_fd, &c, 1);
    // if new data is available on the console, send it to the serial port

  tcsetattr(STDOUT_FILENO, TCSANOW, &old_stdio);


Cutout 2: How to detect your UART

Pseudo Code from Page 52:

Set the value "0xE7" to the FCR to test the status of the FIFO flags. Read the value of the IIR to test for what flags actually got set.

If Bit 6 is set Then If Bit 7 is set Then If Bit 5 is set Then UART is 16750 Else UART is 16550A End If Else UART is 16550 End If Else you know the chip doesn't use FIFO, so we need to check the scratch register Set some arbitrary value like 0x2A to the Scratch Register. You don't want to use 0xFF or 0x00 as those might be returned by the Scratch Register instead for a false postive result.

Read the value of the Scratch Register

If the arbitrary value comes back identical UART is 16450 Else UART is 8250 End If End If