Documentation/usb/gadget_printer.rst

===============================
Linux USB Printer Gadget Driver
===============================

06/04/2007

Copyright (C) 2007 Craig W. Nadler <craig@nadler.us>


General
=======

This driver may be used if you are writing printer firmware using Linux as
the embedded OS. This driver has nothing to do with using a printer with
your Linux host system.

You will need a USB device controller and a Linux driver for it that accepts
a gadget / "device class" driver using the Linux USB Gadget API. After the
USB device controller driver is loaded then load the printer gadget driver.
This will present a printer interface to the USB Host that your USB Device
port is connected to.

This driver is structured for printer firmware that runs in user mode. The
user mode printer firmware will read and write data from the kernel mode
printer gadget driver using a device file. The printer returns a printer status
byte when the USB HOST sends a device request to get the printer status.  The
user space firmware can read or write this status byte using a device file
/dev/g_printer . Both blocking and non-blocking read/write calls are supported.


Howto Use This Driver
=====================

To load the USB device controller driver and the printer gadget driver. The
following example uses the Netchip 2280 USB device controller driver::

	modprobe net2280
	modprobe g_printer


The follow command line parameter can be used when loading the printer gadget
(ex: modprobe g_printer idVendor=0x0525 idProduct=0xa4a8 ):

idVendor
	This is the Vendor ID used in the device descriptor. The default is
	the Netchip vendor id 0x0525. YOU MUST CHANGE TO YOUR OWN VENDOR ID
	BEFORE RELEASING A PRODUCT. If you plan to release a product and don't
	already have a Vendor ID please see www.usb.org for details on how to
	get one.

idProduct
	This is the Product ID used in the device descriptor. The default
	is 0xa4a8, you should change this to an ID that's not used by any of
	your other USB products if you have any. It would be a good idea to
	start numbering your products starting with say 0x0001.

bcdDevice
	This is the version number of your product. It would be a good idea
	to put your firmware version here.

iManufacturer
	A string containing the name of the Vendor.

iProduct
	A string containing the Product Name.

iSerialNum
	A string containing the Serial Number. This should be changed for
	each unit of your product.

iPNPstring
	The PNP ID string used for this printer. You will want to set
	either on the command line or hard code the PNP ID string used for
	your printer product.

qlen
	The number of 8k buffers to use per endpoint. The default is 10, you
	should tune this for your product. You may also want to tune the
	size of each buffer for your product.


Using The Example Code
======================

This example code talks to stdout, instead of a print engine.

To compile the test code below:

1) save it to a file called prn_example.c
2) compile the code with the follow command::

	 gcc prn_example.c -o prn_example


To read printer data from the host to stdout::

	# prn_example -read_data


To write printer data from a file (data_file) to the host::

	# cat data_file | prn_example -write_data


To get the current printer status for the gadget driver:::

	# prn_example -get_status

	Printer status is:
	     Printer is NOT Selected
	     Paper is Out
	     Printer OK


To set printer to Selected/On-line::

	# prn_example -selected


To set printer to Not Selected/Off-line::

	# prn_example -not_selected


To set paper status to paper out::

	# prn_example -paper_out


To set paper status to paper loaded::

	# prn_example -paper_loaded


To set error status to printer OK::

	# prn_example -no_error


To set error status to ERROR::

	# prn_example -error


Example Code
============

::


  #include <stdio.h>
  #include <stdlib.h>
  #include <fcntl.h>
  #include <linux/poll.h>
  #include <sys/ioctl.h>
  #include <linux/usb/g_printer.h>

  #define PRINTER_FILE			"/dev/g_printer"
  #define BUF_SIZE			512


  /*
   * 'usage()' - Show program usage.
   */

  static void
  usage(const char *option)		/* I - Option string or NULL */
  {
	if (option) {
		fprintf(stderr,"prn_example: Unknown option \"%s\"!\n",
				option);
	}

	fputs("\n", stderr);
	fputs("Usage: prn_example -[options]\n", stderr);
	fputs("Options:\n", stderr);
	fputs("\n", stderr);
	fputs("-get_status    Get the current printer status.\n", stderr);
	fputs("-selected      Set the selected status to selected.\n", stderr);
	fputs("-not_selected  Set the selected status to NOT selected.\n",
			stderr);
	fputs("-error         Set the error status to error.\n", stderr);
	fputs("-no_error      Set the error status to NO error.\n", stderr);
	fputs("-paper_out     Set the paper status to paper out.\n", stderr);
	fputs("-paper_loaded  Set the paper status to paper loaded.\n",
			stderr);
	fputs("-read_data     Read printer data from driver.\n", stderr);
	fputs("-write_data    Write printer sata to driver.\n", stderr);
	fputs("-NB_read_data  (Non-Blocking) Read printer data from driver.\n",
			stderr);
	fputs("\n\n", stderr);

	exit(1);
  }


  static int
  read_printer_data()
  {
	struct pollfd	fd[1];

	/* Open device file for printer gadget. */
	fd[0].fd = open(PRINTER_FILE, O_RDWR);
	if (fd[0].fd < 0) {
		printf("Error %d opening %s\n", fd[0].fd, PRINTER_FILE);
		close(fd[0].fd);
		return(-1);
	}

	fd[0].events = POLLIN | POLLRDNORM;

	while (1) {
		static char buf[BUF_SIZE];
		int bytes_read;
		int retval;

		/* Wait for up to 1 second for data. */
		retval = poll(fd, 1, 1000);

		if (retval && (fd[0].revents & POLLRDNORM)) {

			/* Read data from printer gadget driver. */
			bytes_read = read(fd[0].fd, buf, BUF_SIZE);

			if (bytes_read < 0) {
				printf("Error %d reading from %s\n",
						fd[0].fd, PRINTER_FILE);
				close(fd[0].fd);
				return(-1);
			} else if (bytes_read > 0) {
				/* Write data to standard OUTPUT (stdout). */
				fwrite(buf, 1, bytes_read, stdout);
				fflush(stdout);
			}

		}

	}

	/* Close the device file. */
	close(fd[0].fd);

	return 0;
  }


  static int
  write_printer_data()
  {
	struct pollfd	fd[1];

	/* Open device file for printer gadget. */
	fd[0].fd = open (PRINTER_FILE, O_RDWR);
	if (fd[0].fd < 0) {
		printf("Error %d opening %s\n", fd[0].fd, PRINTER_FILE);
		close(fd[0].fd);
		return(-1);
	}

	fd[0].events = POLLOUT | POLLWRNORM;

	while (1) {
		int retval;
		static char buf[BUF_SIZE];
		/* Read data from standard INPUT (stdin). */
		int bytes_read = fread(buf, 1, BUF_SIZE, stdin);

		if (!bytes_read) {
			break;
		}

		while (bytes_read) {

			/* Wait for up to 1 second to sent data. */
			retval = poll(fd, 1, 1000);

			/* Write data to printer gadget driver. */
			if (retval && (fd[0].revents & POLLWRNORM)) {
				retval = write(fd[0].fd, buf, bytes_read);
				if (retval < 0) {
					printf("Error %d writing to %s\n",
							fd[0].fd,
							PRINTER_FILE);
					close(fd[0].fd);
					return(-1);
				} else {
					bytes_read -= retval;
				}

			}

		}

	}

	/* Wait until the data has been sent. */
	fsync(fd[0].fd);

	/* Close the device file. */
	close(fd[0].fd);

	return 0;
  }


  static int
  read_NB_printer_data()
  {
	int		fd;
	static char	buf[BUF_SIZE];
	int		bytes_read;

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR|O_NONBLOCK);
	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	while (1) {
		/* Read data from printer gadget driver. */
		bytes_read = read(fd, buf, BUF_SIZE);
		if (bytes_read <= 0) {
			break;
		}

		/* Write data to standard OUTPUT (stdout). */
		fwrite(buf, 1, bytes_read, stdout);
		fflush(stdout);
	}

	/* Close the device file. */
	close(fd);

	return 0;
  }


  static int
  get_printer_status()
  {
	int	retval;
	int	fd;

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR);
	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	/* Make the IOCTL call. */
	retval = ioctl(fd, GADGET_GET_PRINTER_STATUS);
	if (retval < 0) {
		fprintf(stderr, "ERROR: Failed to set printer status\n");
		return(-1);
	}

	/* Close the device file. */
	close(fd);

	return(retval);
  }


  static int
  set_printer_status(unsigned char buf, int clear_printer_status_bit)
  {
	int	retval;
	int	fd;

	retval = get_printer_status();
	if (retval < 0) {
		fprintf(stderr, "ERROR: Failed to get printer status\n");
		return(-1);
	}

	/* Open device file for printer gadget. */
	fd = open(PRINTER_FILE, O_RDWR);

	if (fd < 0) {
		printf("Error %d opening %s\n", fd, PRINTER_FILE);
		close(fd);
		return(-1);
	}

	if (clear_printer_status_bit) {
		retval &= ~buf;
	} else {
		retval |= buf;
	}

	/* Make the IOCTL call. */
	if (ioctl(fd, GADGET_SET_PRINTER_STATUS, (unsigned char)retval)) {
		fprintf(stderr, "ERROR: Failed to set printer status\n");
		return(-1);
	}

	/* Close the device file. */
	close(fd);

	return 0;
  }


  static int
  display_printer_status()
  {
	char	printer_status;

	printer_status = get_printer_status();
	if (printer_status < 0) {
		fprintf(stderr, "ERROR: Failed to get printer status\n");
		return(-1);
	}

	printf("Printer status is:\n");
	if (printer_status & PRINTER_SELECTED) {
		printf("     Printer is Selected\n");
	} else {
		printf("     Printer is NOT Selected\n");
	}
	if (printer_status & PRINTER_PAPER_EMPTY) {
		printf("     Paper is Out\n");
	} else {
		printf("     Paper is Loaded\n");
	}
	if (printer_status & PRINTER_NOT_ERROR) {
		printf("     Printer OK\n");
	} else {
		printf("     Printer ERROR\n");
	}

	return(0);
  }


  int
  main(int  argc, char *argv[])
  {
	int	i;		/* Looping var */
	int	retval = 0;

	/* No Args */
	if (argc == 1) {
		usage(0);
		exit(0);
	}

	for (i = 1; i < argc && !retval; i ++) {

		if (argv[i][0] != '-') {
			continue;
		}

		if (!strcmp(argv[i], "-get_status")) {
			if (display_printer_status()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-paper_loaded")) {
			if (set_printer_status(PRINTER_PAPER_EMPTY, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-paper_out")) {
			if (set_printer_status(PRINTER_PAPER_EMPTY, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-selected")) {
			if (set_printer_status(PRINTER_SELECTED, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-not_selected")) {
			if (set_printer_status(PRINTER_SELECTED, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-error")) {
			if (set_printer_status(PRINTER_NOT_ERROR, 1)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-no_error")) {
			if (set_printer_status(PRINTER_NOT_ERROR, 0)) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-read_data")) {
			if (read_printer_data()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-write_data")) {
			if (write_printer_data()) {
				retval = 1;
			}

		} else if (!strcmp(argv[i], "-NB_read_data")) {
			if (read_NB_printer_data()) {
				retval = 1;
			}

		} else {
			usage(argv[i]);
			retval = 1;
		}
	}

	exit(retval);
  }