DOC HOME SITE MAP MAN PAGES GNU INFO SEARCH PRINT BOOK
 
HDK Technical Reference

Channel number

The channel number is a DDI 8 abstraction that holds driver-specific information such as channel types, sub-component addresses, and modes. The device instance (see ``Device instance'') represents the specific device. The channel number abstraction is supported in DDI versions 8 and later, and replaces the per-device portion of the minor number.

The pointer to the channel number is set on entry; the driver may change it to redirect the open(D2) routine to another channel to implement channel redirection or ``cloning''. The cloning device only needs one node, which corresponds to a device instance; each clone generated out of that node is a channel.

DDI 8 drivers define the largest channel number that is accessible to the driver instance by setting the $maxchan field in their Node(DSP/4dsp) files. If only one channel is accessible to the driver instance, this field is set to $maxchan 0.

The SVR5 implemtation uses a 32-bit channel number, but the filesystem implementation only provides device space for about 2^20 channels; most devices need significantly fewer channels.


© 2005 The SCO Group, Inc. All rights reserved.
OpenServer 6 and UnixWare (SVR5) HDK - June 2005