Jonathan Stone <jonathan@DSG.Stanford.EDU> wrote

> Documentation on the TC Alpha is more complete and detailed than the
> TC DECstations.  It's also publically available ;) The ioctl asic
> chips are the same, down to different stepping differences.  
> If the Alpha documentation says there's an interlock between SCSI and
> Lance DMA it's _almost_ certainly so for the DECstations as well.

In Digital Technical Journal Vol.4 No. 4 1992, an article titled "The
Design of the DEC 3000 AXP Systems, Two High-performance
Workstations," the author refers why TCDS ASIC was designed adandoning
IOCTL scsi curcuitry.  On page 10, I can see;

  [auther is refering to advantages, TCDS offers dual channels, then ...]

Second, this design elimanates contention between the Ethernet
controller and the SCSI controller for IOCTL bus.  Third, the TCDS
ASIC supports much longer TURBOchannel DMA bursts (64-byte burst
rather than 16-byte burst).

  [4th point is, TCDS ASIC could also be used with PMAZB/PMAZC option cards]

Anyway, I'm dreaming of the day when NetBSD/pmax fully utilizes the
IOCTL ASIC capabilities will be realized.  I firmly believe in there is
more room for improvements of TC DECstation and TC Alpha NetBSDs. 

Tohru Nishimura
Information Technology Centre
Nara Institute of Science and Technology