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diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt deleted file mode 100644 index ce0c1a9b8aab..000000000000 --- a/Documentation/serial/serial-rs485.txt +++ /dev/null @@ -1,95 +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 - implement the rs485_config callback in the uart_port structure. The - serial_core calls rs485_config to do the device specific part in response - to TIOCSRS485 and TIOCGRS485 ioctls (see below). The rs485_config callback - receives a pointer to struct serial_rs485. - -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> - - /* Include definition for RS485 ioctls: TIOCGRS485 and TIOCSRS485 */ - #include <sys/ioctl.h> - - /* 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 while 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/uapi/linux/serial.h - [2] Documentation/devicetree/bindings/serial/rs485.txt |