BSD 4.2 minphys() < 64K

[System Mangler]

In article <376 at wyszecki.munsell.UUCP>, jwf at munsell.UUCP (Jim Franklin) writes:
> I would like to be able to blast a 1/4 megabyte to a disk in one i/o --
> the disk, disk controller, and device driver can all deal with this.

What kind of disk controller?

In article <4763 at mimsy.UUCP>, chris at mimsy.UUCP (Chris Torek) writes:
> The MBA byte count register is 32 bits wide,

The MBA byte count register contains two 16-bit byte counts:  the
number of bytes transferred to/from memory, and the number transferred
to/from the drive.  On an error, they may differ, due to buffering.
The 16-bit byte counts limit the MBA to at most 127 sectors at a time.

The massbus disk driver really ought to supply its own minphys to deal
with 516 byte sectors (which happen when you're writing the headers).

> At 63k-at-a-time, I get a raw data rate of
> 1.1Mb/s on a Vax 785 with Eagles on an Emulex SC788

Even a lowly 750 can do that, given Eagles.

> This amounts to less than 20 interrupts per second---quite trivial;

Lost revolutions, not interrupts, are the issue, and only when you're
doing fairly specialized things, like a database writing raw cylinders,
fast bad-block checking, or image backup to a 200-ips 6250-bpi streamer,
all of which probably require more CPU horsepower than a VAX anyway.

Don Speck   speck at vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck