UART.cpp

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/*
 * for uart programming on linux see the following tutorial
 * https://en.wikibooks.org/wiki/Serial_Programming/termios
 */
 
#include "com/UART.hpp"
 
/* file control options */
#include <fcntl.h>
/* needed for memset */
#include <cstring>
/* for uart baud rate settings etc. */
#include <termios.h>
#include <unistd.h>
#include <iostream>
/* for size_t */
#include <cstddef>
 
UART::~UART() {
}
 
void UART::VConnect() {
  /* TODO: how do we know, that we have to listen on THS1 instead of THS0 e.g.
   * we need a reference here and also a description of how or where to find
   * that information
   * https://stackoverflow.com/questions/2530096/how-to-find-all-serial-devices-ttys-ttyusb-on-linux-without-opening-them
   * Description: pinmux is needed by the kernel to know the HW setup
   *
   * THS = Tegra High Speed
   * ls /dev/ttyS* and
   * ls /dev/ttyTHS* are the same UART HW but different driver
   *
   * on agx:
   * "The initial pinmux should set all of the these pins, except for the power,
   * UART RX TX and two I2C busses, to GPIO at boot. The UART and I2C busses
   * should not be used for GPIO."
   * 
   * pinmux manually on agx:
   * https://www.elinux.org/Jetson/AGX_Xavier_Update_Pinmux_Manually
   *
   * for all uart pinmuxs:
   * sudo cat /sys/kernel/debug/tegra_pinctrl_reg
   *
   * Linux setserial tool:
   * https://www.cyberciti.biz/faq/find-out-linux-serial-ports-with-setserial/
   *
   * Jetson AGX Header Pinout:
   * https://www.jetsonhacks.com/nvidia-jetson-agx-xavier-gpio-header-pinout/
   * taken from:
   * http://developer.nvidia.com/embedded/dlc/jetson-xavier-developer-kit-carrier-board-spec
   *
   * Xavier Forum Links:
   * https://devtalk.nvidia.com/default/topic/1058946/
   *
   * from
   * https://devtalk.nvidia.com/default/topic/1062552/jetson-agx-xavier/accesseing-uart2-in-tegra/post/5380741/#5380741
   * device tree determines routing of serial devices or what function a GPIO
   * will take
   * DT is included in BSP -> HW changes, but drivers stay the same
   *
   * ls -l /dev/ttyS* /dev/ttyTHS*
   * if group name is dialout -> it is connected to some serial HW
   *
   * Additional Information:
   * reverse DTB
   * https://forum.digilentinc.com/topic/2427-how-to-decompile-dtb-file/
   *
   * DT reference: https://elinux.org/Device_Tree_Reference
   *
   * devicetree.org
   * 
   */
#ifndef JETSON_DEVICE
#error "Please define JETSON_DEVICE variable"
#endif
#if JETSON_DEVICE == 0
  const char* ttyPath = "/dev/ttyTHS0";
#else
  const char* ttyPath = "/dev/ttyTHS1";
#endif
  speed_t speed = B1000000; /* 1MBps Baudrate */
  tty_fd        = open(ttyPath, O_RDWR | O_NOCTTY | O_SYNC);
 
  if(tty_fd < 0) {
    std::cout << "ERROR: Could not open tty " << *ttyPath;
    return;
  }
 
  struct termios tty;
  memset(&tty, 0, sizeof tty);
 
  tty.c_iflag     = 0;
  tty.c_oflag     = 0;
  tty.c_cflag     = (CS8 | CLOCAL | CREAD);
  tty.c_lflag     = 0;
  tty.c_cc[VMIN]  = 1;
  tty.c_cc[VTIME] = 5;
 
  cfsetospeed(&tty, speed);
  cfsetispeed(&tty, speed);
 
  tcsetattr(tty_fd, TCSANOW, &tty);
 
  tcflush(tty_fd, TCIOFLUSH);
 
  m_connected = true;
}
 
void UART::VDisconnect() {
  if(tty_fd < 0) {
    return;
  }
  close(tty_fd);
 
  m_connected = false;
}
 
size_t UART::VSendData(void* pData, const size_t len) {
  size_t written = write(tty_fd, pData, len);
  return written;
}
 
size_t UART::VReceiveData(void* pData, const size_t len) {
  size_t bytesread = read(tty_fd, pData, len);
  return bytesread;
}
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