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 erw_eadm — EADM Subchannel 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 esw_eadm — EADM Subchannel 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
pathmask_to_pos — find the position of the left-most bit in a pathmask

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.