bbb_cape/src/bbb/uart_receiver.cc

#include "bbb/uart_receiver.h"

#include <fcntl.h>
#include <linux/serial.h>
#include <termio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <inttypes.h>

#include <algorithm>

#include "aos/common/logging/logging.h"
#include "bbb_cape/src/cape/cows.h"
#include "bbb/crc.h"

// This is the code for receiving data from the cape via UART.
// NOTE: In order for this to work, you MUST HAVE
// "capemgr.enable_partno=BB_UART1"
// in your BBB's /media/BEAGLEBONE/uEnv.txt file!

// Implementation for setting custom serial baud rates based on this code:
// <http://jim.sh/ftx/files/linux-custom-baudrate.c>

namespace bbb {
namespace {
// TODO(brians): Determine this in some way that allows easy switching for
// testing with /dev/ttyUSB0 for example.
const char *device = "/dev/ttyO1";
}  // namespace

UartReceiver::UartReceiver(int32_t baud_rate)
    : baud_rate_(baud_rate),
      buf_(new AlignedChar[DATA_STRUCT_SEND_SIZE]),
      fd_(open(device, O_RDWR | O_NOCTTY)) {
  static_assert((DATA_STRUCT_SEND_SIZE % 4) == 0,
                "We can't do checksums of lengths that aren't multiples of 4.");

  if (fd_ < 0) {
    LOG(FATAL, "open(%s, O_RDWR | O_NOCTTY) failed with %d: %s."
               " Did you read my note in bbb/uart_receiver.cc?\n",
        device, errno, strerror(errno));
  }
 
  serial_struct serinfo;
  // Must implement an ugly custom divisor.
  serinfo.reserved_char[0] = 0;
  if (ioctl(fd_, TIOCGSERIAL, &serinfo) < 0) {
    LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
        fd_, &serinfo, errno, strerror(errno));
  }
  serinfo.flags &= ~ASYNC_SPD_MASK;
  serinfo.flags |= ASYNC_SPD_CUST;
  serinfo.custom_divisor = (serinfo.baud_base + (baud_rate_ / 2)) / baud_rate_;
  if (serinfo.custom_divisor < 1) serinfo.custom_divisor = 1;
  if (ioctl(fd_, TIOCSSERIAL, &serinfo) < 0) {
    LOG(FATAL, "ioctl(%d, TIOCSSERIAL, %p) failed with %d: %s\n",
        fd_, &serinfo, errno, strerror(errno));
  }
  if (ioctl(fd_, TIOCGSERIAL, &serinfo) < 0) {
    LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
        fd_, &serinfo, errno, strerror(errno));
  }
  if (serinfo.custom_divisor * baud_rate_ != serinfo.baud_base) {
    LOG(WARNING, "actual baudrate is %d / %d = %f\n",
        serinfo.baud_base, serinfo.custom_divisor,
        static_cast<double>(serinfo.baud_base) / serinfo.custom_divisor);
  }

  if (fcntl(fd_, F_SETFL, 0) != 0) {
    LOG(FATAL, "fcntl(%d, F_SETFL, 0) failed with %d: %s\n",
        fd_, errno, strerror(errno));
  }

  termios options;
  if (tcgetattr(fd_, &options) != 0) {
    LOG(FATAL, "tcgetattr(%d, %p) failed with %d: %s\n",
        fd_, &options, errno, strerror(errno));
  }
  if (cfsetispeed(&options, B38400) != 0) {
    LOG(FATAL, "cfsetispeed(%p, B38400) failed with %d: %s\n",
        &options, errno, strerror(errno));
  }
  if (cfsetospeed(&options, B38400) != 0) {
    LOG(FATAL, "cfsetospeed(%p, B38400) failed with %d: %s\n",
        &options, errno, strerror(errno));
  }
  cfmakeraw(&options);
  options.c_cflag |= (CLOCAL | CREAD);
  options.c_cflag &= ~CRTSCTS;
  options.c_iflag = 0;
  options.c_oflag = 0;
  options.c_lflag = 0;
  options.c_cc[VMIN] = 0;
  options.c_cc[VTIME] = 1;
  if (tcsetattr(fd_, TCSANOW, &options) != 0) {
    LOG(FATAL, "tcsetattr(%d, TCSANOW, %p) failed with %d: %s\n",
        fd_, &options, errno, strerror(errno));
  }
}

UartReceiver::~UartReceiver() {
  delete buf_;
  if (fd_ > 0) close(fd_);
}

bool UartReceiver::FindPacket() {
  // How many 0 bytes we've found at the front so far.
  int zeros_found = 0;
  // How many bytes of the packet we've read in (or -1 if we don't know where
  // the packet is).
  int packet_bytes = -1;
  while (true) {
    size_t already_read = ::std::max(packet_bytes, 0);
    ssize_t new_bytes =
        read(fd_, buf_ + already_read, DATA_STRUCT_SEND_SIZE - already_read);
    if (new_bytes < 0) {
      if (errno == EINTR) continue;
      LOG(WARNING, "read(%d, %p, %zd) failed with %d: %s\n",
          fd_, buf_ + already_read, DATA_STRUCT_SEND_SIZE - already_read,
          errno, strerror(errno));
      return false;
    }

    if (packet_bytes == -1) {
      // Find the beginning of the packet (aka look for four zero bytes).
      for (ssize_t checked = 0; checked < new_bytes; ++checked) {
        if (buf_[checked] == 0) {
          ++zeros_found;
          if (zeros_found == 4) {
            packet_bytes = new_bytes - checked - 1;
            memmove(buf_, buf_ + checked + 1, packet_bytes);
            break;
          }
        } else {
          zeros_found = 0;
        }
      }
    } else {  // we think there's a packet at the beginning of our buffer
      for (int to_check = packet_bytes; packet_bytes + new_bytes; ++to_check) {
        // We shouldn't find any 0s in the middle of what should be a packet.
        if (buf_[to_check] == 0) {
          packet_bytes = -1;
          break;
        }
      }
      packet_bytes += new_bytes;
      if (packet_bytes == DATA_STRUCT_SEND_SIZE) return true;
    }
  }
}

bool UartReceiver::GetPacket(DataStruct *packet) {
  if (!FindPacket()) return false;

  uint32_t unstuffed = cows_unstuff(reinterpret_cast<uint32_t *>(buf_),
                                    DATA_STRUCT_SEND_SIZE / 4,
                                    reinterpret_cast<uint32_t *>(packet));
  if (unstuffed == 0) {
    LOG(WARNING, "invalid packet\n");
  } else if (unstuffed != sizeof(packet)) {
    LOG(WARNING, "packet is %" PRIu32 " words instead of %" PRIu32 "\n",
        unstuffed, DATA_STRUCT_SEND_SIZE / 4);
  }

  // Make sure the checksum checks out.
  uint32_t checksum;
  memcpy(&checksum, buf_ + DATA_STRUCT_SEND_SIZE - 4, 4);
  if (cape::CalculateChecksum(reinterpret_cast<uint8_t *>(packet),
                              sizeof(DataStruct)) != checksum) {
    LOG(WARNING, "Rejecting packet due to checksum failure.\n");
    return false;
  }

  return true;
}

}  // namespace bbb