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diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt deleted file mode 100644 index 41c8378c0b2..00000000000 --- a/Documentation/serial/serial-rs485.txt +++ /dev/null @@ -1,136 +0,0 @@ - RS485 SERIAL COMMUNICATIONS - -1. INTRODUCTION - - EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the - electrical characteristics of drivers and receivers for use in balanced - digital multipoint systems. - This standard is widely used for communications in industrial automation - because it can be used effectively over long distances and in electrically - noisy environments. - -2. HARDWARE-RELATED CONSIDERATIONS - - Some CPUs/UARTs (e.g., Atmel AT91 or 16C950 UART) contain a built-in - half-duplex mode capable of automatically controlling line direction by - toggling RTS or DTR signals. That can be used to control external - half-duplex hardware like an RS485 transceiver or any RS232-connected - half-duplex devices like some modems. - - For these microcontrollers, the Linux driver should be made capable of - working in both modes, and proper ioctls (see later) should be made - available at user-level to allow switching from one mode to the other, and - vice versa. - -3. DATA STRUCTURES ALREADY AVAILABLE IN THE KERNEL - - The Linux kernel provides the serial_rs485 structure (see [1]) to handle - RS485 communications. This data structure is used to set and configure RS485 - parameters in the platform data and in ioctls. - - The device tree can also provide RS485 boot time parameters (see [2] - for bindings). The driver is in charge of filling this data structure from - the values given by the device tree. - - Any driver for devices capable of working both as RS232 and RS485 should - provide at least the following ioctls: - - - TIOCSRS485 (typically associated with number 0x542F). This ioctl is used - to enable/disable RS485 mode from user-space - - - TIOCGRS485 (typically associated with number 0x542E). This ioctl is used - to get RS485 mode from kernel-space (i.e., driver) to user-space. - - In other words, the serial driver should contain a code similar to the next - one: - - static struct uart_ops atmel_pops = { - /* ... */ - .ioctl = handle_ioctl, - }; - - static int handle_ioctl(struct uart_port *port, - unsigned int cmd, - unsigned long arg) - { - struct serial_rs485 rs485conf; - - switch (cmd) { - case TIOCSRS485: - if (copy_from_user(&rs485conf, - (struct serial_rs485 *) arg, - sizeof(rs485conf))) - return -EFAULT; - - /* ... */ - break; - - case TIOCGRS485: - if (copy_to_user((struct serial_rs485 *) arg, - ..., - sizeof(rs485conf))) - return -EFAULT; - /* ... */ - break; - - /* ... */ - } - } - - -4. USAGE FROM USER-LEVEL - - From user-level, RS485 configuration can be get/set using the previous - ioctls. For instance, to set RS485 you can use the following code: - - #include <linux/serial.h> - - /* Driver-specific ioctls: */ - #define TIOCGRS485 0x542E - #define TIOCSRS485 0x542F - - /* Open your specific device (e.g., /dev/mydevice): */ - int fd = open ("/dev/mydevice", O_RDWR); - if (fd < 0) { - /* Error handling. See errno. */ - } - - struct serial_rs485 rs485conf; - - /* Enable RS485 mode: */ - rs485conf.flags |= SER_RS485_ENABLED; - - /* Set logical level for RTS pin equal to 1 when sending: */ - rs485conf.flags |= SER_RS485_RTS_ON_SEND; - /* or, set logical level for RTS pin equal to 0 when sending: */ - rs485conf.flags &= ~(SER_RS485_RTS_ON_SEND); - - /* Set logical level for RTS pin equal to 1 after sending: */ - rs485conf.flags |= SER_RS485_RTS_AFTER_SEND; - /* or, set logical level for RTS pin equal to 0 after sending: */ - rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND); - - /* Set rts delay before send, if needed: */ - rs485conf.delay_rts_before_send = ...; - - /* Set rts delay after send, if needed: */ - rs485conf.delay_rts_after_send = ...; - - /* Set this flag if you want to receive data even whilst sending data */ - rs485conf.flags |= SER_RS485_RX_DURING_TX; - - if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) { - /* Error handling. See errno. */ - } - - /* Use read() and write() syscalls here... */ - - /* Close the device when finished: */ - if (close (fd) < 0) { - /* Error handling. See errno. */ - } - -5. REFERENCES - - [1] include/linux/serial.h - [2] Documentation/devicetree/bindings/serial/rs485.txt |