File open on Snapdragon Flight DSP returning suspiciously large number

Question

Why, when calling open("/dev/tty-2",O_RDWR); is the open file number 268435355 (eg -1+2^28)? Is this a normal sized number to output from open() call on a real-time operating system (like android DSP side)? It seems too large.

DSP processor running Qualcomm Real-Time OS. Other processor running Linaro Linux.

Pertinent output from mini-dm, DSP (digital signal processor) runtime debugger:

Running mini-dm version: 3.0
Device found with Product ID 0x9025. Continuing...
mini-dm is waiting for a DMSS connection...
DMSS is connected. Running mini-dm...
[08500/03]  00:40.640  HAP:63:HAP_debug_v2 weak ref not found, return _rtld_sym_zero@_rtld_objmain  0294  symbol.c
[08500/03]  00:40.640  HAP:63:HAP_debug_v2 weak ref not found, return _rtld_sym_zero@_rtld_objmain  0294  symbol.c
[08500/02]  00:40.640  HAP:63:Opening serial port  0062  helloworld_dsp.c
[08500/00]  00:40.640  configuring UART for 4-wire mode, DAL id: 0x2001005  0852  DalUart.c
[08500/02]  00:40.641  HAP:63:Opened serial port number 268435455  0065  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Closing serial port  0075  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Successfully closed serial port number 268435455  0078  helloworld_dsp.c
[08500/02]  00:40.641  HAP:63:Opening serial port  0062  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:workaround: reopening an existing serial port  0351  serial.c
[08500/02]  00:40.642  HAP:63:Opened serial port number 268435455  0065  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Beginning serial read  0123  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:/dev/tty-2 read bytes [0]:   0129  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Closing serial port  0075  helloworld_dsp.c
[08500/02]  00:40.642  HAP:63:Successfully closed serial port number 268435455  0078  helloworld_dsp.c

Pertinent DSP code:

int example_interface_serial_open()
{
LOG_INFO("Opening serial port");
  serial_fds[0] = open(serial_path[0],O_RDWR);
  if (serial_fds[0] >= SUCCESS) {
    LOG_INFO("Opened serial port number %d", serial_fds[0]);
  } else {
  //FIXME log error!
LOG_INFO("Error opening serial port");
    serial_fds[0] = ERROR;
  }
  return serial_fds[0];
}

int example_interface_serial_close(int fd) {
LOG_INFO("Closing serial port");

  if (!close(fd)) {
    LOG_INFO("Successfully closed serial port number %d", fd);
  } else {
    LOG_INFO("Error closing serial port");
    fd = ERROR;
  }

  return fd;
}

int example_interface_serial_read(int fd) {
  int res = SUCCESS;
  char rx_buffer[SERIAL_SIZE_OF_DATA_BUFFER];
  unsigned int num_bytes_read;
  int active_devices = 0;
  int runs, i;

  LOG_INFO("Beginning serial read");

  memset(rx_buffer, 0, SERIAL_SIZE_OF_DATA_BUFFER);
  num_bytes_read = read(fd, rx_buffer,
      SERIAL_SIZE_OF_DATA_BUFFER);
  LOG_INFO("%s read bytes [%d]: %s",
      serial_path[0], num_bytes_read, rx_buffer);

  if (res < SUCCESS) {
    LOG_INFO("Closing file %s",
      serial_path[0]);
    close(fd);
    fd = ERROR;
  }

return fd;
}

Edit: including definition of LOG_INFO()

/****************************************************************************
 * Copyright (C) 2015 Mark Charlebois. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name ATLFlight nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/
#pragma once

#ifdef __cplusplus
extern "C" {
#endif

#ifdef __hexagon__
// Debug output on the aDSP
#include <HAP_farf.h>

#define LOG_INFO(...) FARF(ALWAYS, __VA_ARGS__);
#define LOG_ERR(...) FARF(ALWAYS, __VA_ARGS__);
#define LOG_DEBUG(...) FARF(MEDIUM, __VA_ARGS__);

#else
// Debug output on the apps processor
#include <stdio.h>
#define LOG_INFO(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)
#define LOG_ERR(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)
#define LOG_DEBUG(...) do{ printf(__VA_ARGS__); printf("\n"); } while (0)

#endif

#ifdef __cplusplus
}
#endif

Output of int i=-1; LOG_INFO("%d\n",1);

DSP-side: [08500/02] 02:27.822 HAP:24639: -1 0063 helloworld_dsp.c

Linux-side: -1

Answer 1

From a developer of the device:

The return value from the open() functions is a signed int, and is >= zero for success, and less than zero for failure.

The reason the return value is so large is because it is offset by a known constant of 0x0FFFFFFF. This is done to differentiate device handles from file system handles (file system handles are always less than 0x0FFFFFFF), which are processed differently in the aDSP code.

Quirky! :P