brian at quarterbyte.com
Sun Sep 4 12:42:08 CDT 2005
> ... would it be near to 'plug-and-go' for his
> 3803-controller/3420-drives combination, or would their be a lot
> of 3803-specific software-driver development on the modern-host
> side (and requiring the acquisition of 100 lbs. of 3803 manuals) ?
Pretty much plug and go. It's very much like a SCSI interface.
Each device has a set of commands documented in its Functional
Characteristics manual: read, write, get status, etc. You'd find
this in the device's documentation (e.g. 3420) rather than the
controller's (3803). The commands do follow a common pattern
although there are some variations between devices.
The Bus and Tag protocol communicates these commands from
the channel (the interface in the CPU) to the device controller,
and returns the results. There are several different transfer
modes (byte at a time, burst, etc), different ways that
the device can signal the CPU for attention, and various ways
that either the channel, the controller or the device can
say "hang on, I can't do that right now," so it's fairly
complex. The logic frames for a typical channel interface built
with 1960s vintage SLT are about the same size as the IBM 1130's
CPU, for example. I suspect that data buffers (RAM) are a
significant part of that.
But from the programmer's standpoint, it's very simple. An
IO command points to a "channel program" which is usually just
a device command word and a data transfer address. The channel
takes it from there, and an interrupt is issued when the
operation is complete (usually).
Channel to controller cabling is standardized, two thick
cables. Controller to device cabling is device specific. Some
devices have an integral controller.
_| _| _| Brian Knittel
_| _| _| Quarterbyte Systems, Inc.
_| _| _| Tel: 1-510-559-7930
_| _| _| Fax: 1-510-525-6889
_| _| _| Email: brian at quarterbyte.com
_| _| _| http://www.quarterbyte.com
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