# Device Identifiers

Contents

- Description
  - Serial Device Identifiers
  - USB Device Identifiers
  - Bluetooth Device Identifiers
  - HID Device Identifiers
  - Null Device Identifiers

## Description

The general syntax of a device identifier is:

    qualifier:parameter=value+...

More specifically, with [brackets] meaning optional, the syntax is:

    [qualifier:][parameter=]value[+parameter=value]...

The qualifier specifies which class of device is being identified. It is separated from the rest of the device identifier by a colon (`:`). It may be one of:

> Qualifier | Assumed First Parameter
> serial: | name=
> usb: | serialNumber=
> bluetooth: | address=
> hid: | address=
> null: |

The qualifier is case insensitive, and any abbreviation may be used. For backward compatibility (to when a device identifier was strictly interpreted as the absolute path to a serial device), the qualifier (along with its colon delimiter) is optional, and, if it isn't supplied, `serial` is assumed.

One or more parameters may be supplied after the qualifier. Each parameter is specified as its name and its value, in that order, separated by an equals (`=`) sign. Parameters are separated from one another by a plus (`+`) sign. Parameter names are case insensitive, and any abbreviation may be used. Supplying a zero-length value means to use the parameter's default value.

For backward compatibility (to when device identifier parameters weren't supported), the first supplied parameter is special in that its name (along with its equals sign delimiter) is optional. If the name of the first parameter isn't supplied then the class-dependent parameter that most specifically identifies the device is assumed. See the table above for which parameter is assumed for each class.

It isn't possible to supply no parameters at all. Specifying only the qualifier is equivalent to also specifying a zero-length value for the assumed first parameter for that class. For example, specifying `usb:` is equivalent to specifying `usb:serialNumber=`.

An example to illustrate the optionality of both the qualifier and the name of the first supplied parameter:

- On Linux, the name of the first serial device is `ttyS0`. All of the following device identifiers refer to the same serial device:

      serial:name=ttyS0
      serial:ttyS0
      ttyS0
      name=ttyS0

### Serial Device Identifiers

Serial device identifiers support the following parameters:

> Name | Value
> `name` | name of, relative path to, or absolute path to the device
> `baud` | the data transmission/reception rate (bits per second)
> `dataBits` | the number of data bits per character
> `stopBits` | the number of stop bits per character
> `parity` | `none`, `odd`, `even`, `space`, `mark`
> `flowControl` | `none`, `hardware`

All of the parameters are optional, although the `name=` parameter should be supplied. It shouldn't normally be necessary to supply any of the others, especially since, in most cases, the braille driver overrides them.

`name=`
  Specify the host device to use. It must be the name of the device, the relative path to the device, or the absolute path to the device. If it's either a name or a relative path then the host's device directory (usually `/dev` on Unix-based platforms) is used. If this parameter isn't supplied then the primary (first) serial device is assumed.
`baud=`
  Specify the speed, in bits per second, at which to communicate with the device. It must be a positive integer. Typical values are: `9600`, `19200`, `38400`, `57600`, `115200`. If this parameter isn't supplied then `9600` is assumed.
`dataBits=`
  Specify the number of bits to use to represent a character, not including any metadata (start bit, stop bit(s), parity, etc). It must be a positive integer, and is usually within the range `5`-`8`. If this parameter isn't supplied then `8` is assumed.
`stopBits=`
  Specify the number of stop bits to inject after a character has been transmitted and to expect after a character has been received. It must be a positive integer, and is usually either `1` (for higher speeds) or `2` (for lower speeds). If this parameter isn't supplied then `1` is assumed.
`parity=`
  Specify the type of error detection to use. It must be one of: `none`, `odd`, `even`, `space`, `mark`. If this parameter isn't supplied then `none` is assumed.
`flowControl=`
  Specify the kind of flow control to use. It must be one of: `none`, `hardware`. If this parameter isn't supplied then `none` is assumed.

### USB Device Identifiers

USB device identifiers support the following parameters:

> Name | Value
> `serialNumber=` | one or more arbitrary characters
> `vendorIdentifier=` | an integer within the range 1-65535 (0X0001-0XFFFF)
> `productIdentifier=` | an integer within the range 1-65535 (0X0001-0XFFFF)
> `genericDevices=` | `yes`, `no`

All of the parameters are optional. It shouldn't normally be necessary to supply any of them.

`serialNumber=`
  Specify the serial number that the device must have. The match is case sensitive and must be exact. If this parameter isn't supplied then the serial number of the device isn't verified.
`vendorIdentifier=`
  Specify the vendor identifier that the device must have. It must be an integer within the range `1`-`65535` (or, in hexadecimal, `0X0001`-`0XFFFF`). If this parameter isn't supplied then the vendor identifier of the device isn't verified.
`productIdentifier=`
  Specify the product identifier that the device must have. It must be an integer within the range `1`-`65535` (or, in hexadecimal, `0X0001`-`0XFFFF`). If this parameter isn't supplied then the product identifier of the device isn't verified.
`genericDevices=`
  Specify whether or not a device that has a generic vendor/product identifier pair may be used. It's value must be either `yes` or `no`. The check is case insensitive, and any abbreviation may be used. If this parameter isn't supplied then `yes` is assumed.

### Bluetooth Device Identifiers

Bluetooth device identifiers support the following parameters:

> Name | Value
> `address=` | six two-digit hexadecimal numbers separated by `:` or `-`
> `name=` | one or more arbitrary characters
> `channel=` | an integer within the range `1`-`30`
> `discover=` | `yes`, `no`
> `timeout=` | an integer within the range `1`-`59`

All of the parameters are optional except that the `address=` parameter is required on platforms where BRLTTY can't yet detect a Bluetooth device based on its name. It shouldn't normally be necessary to supply any of the others.

BRLTTY can detect a Bluetooth device by name on the following platforms:

- Android
- Linux (if the Bluetooth version is at least 5)
- Windows

`address=`
  Specify the MAC address of the device. It must be six two-digit hexadecimal numbers (the "letter" digits may be in either case) separated from one another by either a colon (`:`) or a minus (`-`) sign.
`name=`
  Specify the name of the device. It must be one or more arbitrary characters. They need only match the beginning (so not necessarily all) of the name. Case is significant. Only the names of paired devices are considered. This parameter is ignored if the `address=` parameter has been specified.
`channel=`
  Specify the RFCOMM channel to use. It must be an integer within the range `1`-`30`. If this parameter isn't supplied then either a driver-supplied default channel number is assumed or service discovery is performed.
`discover=`

  Specify whether or not service discovery is to be performed. In other words, this parameter specifies whether or not the device is to be "asked" for the RFCOMM channel number. It must be either `yes` or `no`. The check is case insensitive, and any abbreviation may be used. If this parameter isn't supplied then whether or not service discovery is performed is decided according to the following sequence of tests:

  1. If the `channel=` parameter has been supplied, then no.
  2. If the driver has requested service discovery, then yes.
  3. If the driver has specified a default channel number, then no.
  4. Otherwise, no.
`timeout=`
  Specify the number of seconds to wait for a connection to the device to be acquired. It must be an integer within the range `1`-`59`. If this parameter isn't supplied then a reasonable default is assumed.

### HID Device Identifiers

HID device identifiers support the following parameters:

> Name | Value
> `address=` | Bluetooth MAC address
> `name=` | Bluetooth device name
> `manufacturer=` | USB device manufacturer
> `description=` | USB product description
> `serialNumber=` | USB serial number
> `vendor=` | four hexadecimal digits
> `product=` | four hexadecimal digits

All of the parameters are optional, although, in most cases, either the `serialNumber=` parameter (for a USB device) or the `address=` parameter (for a Bluetooth device) should be supplied. USB-specific and Bluetooth-specific parameters may not be combined.

`address=`
  The MAC address of a Bluetooth device. It must be six two-digit hexadecimal numbers separated from one another by a colon (`:`). The letter digits may be in either case.
`name=`
  The name of a Bluetooth device. Only the start of the name is matched. Matching is case insensitive.
`manufacturer=`
  The name of the manufacturer of a USB device. Only the start of the name is matched. Matching is case insensitive.
`description=`
  The product description of a USB device. Only the start of the description is matched. Matching is case insensitive.
`serialNumber=`
  The serial number of a USB device. Only the start of the serial number is matched. Matching is case insensitive.
`vendor=`
  The vendor identifier of the device. It must be four hexadecimal digits. The letter digits may be in either case.
`product=`
  The product identifier of the device. It must be four hexadecimal digits. The letter digits may be in either case.

### Null Device Identifiers

A `null` endpoint has the following properties:

- It always indicates that input is available.
- Reading from it always yields end-of-file.
- Writing to it is always successful but does nothing.