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.Dd January 19, 2016
.Dt CAM_PERIPH 9
.Os
.Sh NAME
.Nm cam_periph
.Nd Peripheral driver for CAM
.Sh SYNOPSIS
.In cam/cam_xpt_periph.h
.Sh DESCRIPTION
In CAM, periph drivers translate upper layer requests into protocol
requests that the CAM transport (XPT) delivers to a CAM SIM driver.
.Sh COMPONENTS
.Ss Creating a Periph Driver
Peripheral drivers are created with
.Xr cam_periph_alloc 9
with a number of routines.
The
.Va ctor
function is used to initialize the instance of the driver.
The
.Va oninvalidate
function, if present, is called when CAM determines the driver is no
longer valid.
The
.Va dtor
function is called when the driver is destroyed.
The
.Va start
function is called when CAM allocates a CCB for this periph to do
work.
.Ss Device Queue
Each periph has a device queue associated with it.
The device queue throttles the number of requests that CAM will allow
the periph to generate.
When a request is freed, or other times when the device queue is run,
CAM will call the device's
.Va start
routine with a free CCB.
This is how CAM gets work done in the system.
Periph drivers usually call
.Xr xpt_schedule 9
when they have work to do.
If there's free slots in the device queue, the
.Va start
routine will be called to do it.
CAM also allows limits between devices for total requests at one time
to accommodate SIM drivers for devices that can have fewer total
outstanding transactions than the sum of the transactions each device
can have outstanding.
.Sh TYPES
.Ss ac_callback_t
.Ss ac_code
.Sh SEE ALSO
.Xr cam_periph 9 ,
.Xr xpt_release_ccb 9 ,
.Xr xpt_setup_cbb 9
.Sh AUTHORS
This manual page was written by
.An M. Warner Losh .