[[drivers]]
== E1 drivers

`osmo-e1d` was primarily developed for the icE1usb hardware, but also
supports some other drivers by now.


=== The `usb` driver for icE1usb and e1-tracer

The `usb` driver implements the USB interface first implemented by the
`icE1usb` hardware.

For more information on the `icEusb`, please see its related user
manual, published at https://downloads.osmocom.org/docs/latest/icE1usb-usermanual.pdf

Each `icEusb` device implements one E1 interface with up to two E1
lines.  Note that supporting two E1 lines is only supported on very few
select USB host controllers. In most cases, your USB host controller
will only permit using one of the two lines.

==== Configuration

`osmo-e1d` will automatically detect any supported USB devices when
starting up. It will dynamically allocate E1 interface and E1 line
numbers to those USB devices.  However, the order is not guaranteed and
particularly in case you have multiple devices, it is strongly
recommended to use _static configuration_.

In this static configuration, you would have a block like

.Example configuration snippet for an icE1usb
----
 interface 2 icE1usb
  usb-serial dc697407e7881531
----

This way you reserve/allocate the E1 interface number 2 for the icE1usb
with serial number dc697407e7881531.  The Serial number is unique and
stored in the iSerial string of the USB device descriptor.  You can for
example use `lsusb -v -d 1d50: | grep iSerial` to obtain it, or check
the `dmesg` kernel log after plugging in a device.

==== Using the `usb` driver with `e1-tracer`

The same driver has been slightly extended to also support the passive,
bi-directional `e1-tracer` hardware.  The configuration and use is
identical to the use with the `icE1usb`, with the notable difference
that a passive tracer can obviously only receive data from E1, but not
transmit.  The two directions of a E1 circuit are represented as two
lines in `osmo-e1d`.

=== The `vpair` driver for virtual E1 circuits

Sometimes it is useful to be able to interface multiple E1-using
applications without a real E1 circuit or any hardware whatsoever.

This can be used in automatic / virtualized software testing, but also
in case a legacy application is migrate away from real physical E1
circuits.

==== Configuration

The configuration of the `vpair` driver is relatively simple.  It
consists of a single `virtual-e1-pair` command.

.Example configuration snippet for a virtual E1 pair with one E1 line
----
e1d
 virtual-e1-pair 1
----

The above example will create a virtual pair of E1 interfaces, each
of those interface with one E1 line.

.Log output of the example configuration for 1 virtual pair
----
intf_line.c:184 (I0) Created
intf_line.c:285 (I0:L0) Created
intf_line.c:184 (I1) Created
intf_line.c:285 (I1:L0) Created
----

You can subsequently use the Lines just like you would use physical E1
lines.  Any data you transmit on one line will be received on the other
line, and vice versa.