diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-tty | 19 | ||||
| -rw-r--r-- | Documentation/filesystems/proc.txt | 24 | ||||
| -rw-r--r-- | Documentation/serial/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/serial/serial-rs485.txt | 120 |
4 files changed, 165 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty new file mode 100644 index 00000000000..b138b663bf5 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-tty @@ -0,0 +1,19 @@ +What: /sys/class/tty/console/active +Date: Nov 2010 +Contact: Kay Sievers <kay.sievers@vrfy.org> +Description: + Shows the list of currently configured + console devices, like 'tty1 ttyS0'. + The last entry in the file is the active + device connected to /dev/console. + The file supports poll() to detect virtual + console switches. + +What: /sys/class/tty/tty0/active +Date: Nov 2010 +Contact: Kay Sievers <kay.sievers@vrfy.org> +Description: + Shows the currently active virtual console + device, like 'tty1'. + The file supports poll() to detect virtual + console switches. diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index e73df2722ff..9471225212c 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -1181,6 +1181,30 @@ Table 1-12: Files in /proc/fs/ext4/<devname> mb_groups details of multiblock allocator buddy cache of free blocks .............................................................................. +2.0 /proc/consoles +------------------ +Shows registered system console lines. + +To see which character device lines are currently used for the system console +/dev/console, you may simply look into the file /proc/consoles: + + > cat /proc/consoles + tty0 -WU (ECp) 4:7 + ttyS0 -W- (Ep) 4:64 + +The columns are: + + device name of the device + operations R = can do read operations + W = can do write operations + U = can do unblank + flags E = it is enabled + C = it is prefered console + B = it is primary boot console + p = it is used for printk buffer + b = it is not a TTY but a Braille device + a = it is safe to use when cpu is offline + major:minor major and minor number of the device separated by a colon ------------------------------------------------------------------------------ Summary diff --git a/Documentation/serial/00-INDEX b/Documentation/serial/00-INDEX index 07dcdb0d2a3..e09468ad3cb 100644 --- a/Documentation/serial/00-INDEX +++ b/Documentation/serial/00-INDEX @@ -14,6 +14,8 @@ riscom8.txt - notes on using the RISCom/8 multi-port serial driver. rocket.txt - info on the Comtrol RocketPort multiport serial driver. +serial-rs485.txt + - info about RS485 structures and support in the kernel. specialix.txt - info on hardware/driver for specialix IO8+ multiport serial card. stallion.txt diff --git a/Documentation/serial/serial-rs485.txt b/Documentation/serial/serial-rs485.txt new file mode 100644 index 00000000000..a4932387bbf --- /dev/null +++ b/Documentation/serial/serial-rs485.txt @@ -0,0 +1,120 @@ + 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. + + 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; + + /* Set RS485 mode: */ + rs485conf.flags |= SER_RS485_ENABLED; + + /* Set rts delay before send, if needed: */ + rs485conf.flags |= SER_RS485_RTS_BEFORE_SEND; + rs485conf.delay_rts_before_send = ...; + + /* Set rts delay after send, if needed: */ + rs485conf.flags |= SER_RS485_RTS_AFTER_SEND; + rs485conf.delay_rts_after_send = ...; + + 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 |