Chapter 2. The ccw bus

Table of Contents

I/O functions for channel-attached devices
ccw devices
The channel-measurement facility

The ccw bus typically contains the majority of devices available to a s390 system. Named after the channel command word (ccw), the basic command structure used to address its devices, the ccw bus contains so-called channel attached devices. They are addressed via I/O subchannels, visible on the css bus. A device driver for channel-attached devices, however, will never interact with the subchannel directly, but only via the I/O device on the ccw bus, the ccw device.

I/O functions for channel-attached devices

struct ccw1 - channel command word
struct erw - extended report word
struct sublog - subchannel logout area
struct esw0 - Format 0 Extended Status Word (ESW)
struct esw1 - Format 1 Extended Status Word (ESW)
struct esw2 - Format 2 Extended Status Word (ESW)
struct esw3 - Format 3 Extended Status Word (ESW)
struct irb - interruption response block
struct ciw - command information word (CIW) layout
struct ccw_dev_id - unique identifier for ccw devices
ccw_dev_id_is_equal - compare two ccw_dev_ids

Some hardware structures have been translated into C structures for use by the common I/O layer and device drivers. For more information on the hardware structures represented here, please consult the Principles of Operation.