[HECnet] TOPS-10 KS10 Ethernet Monitor

[Johnny Billquist]

On 2015-04-26 22:22, John Wilson wrote:
> From: Johnny Billquist <bqt at softjar.se>
>
>> I'm curious on exactly how a DEUNA/DELUA works in a KS-10. Does anyone
>> know? Does it do 8-bit-byte DMA to the 18-bit memory, leaving the top
>> two bits alone. Or does it only work if it do word DMA (would be
>> strange, as the controller itself can send and receive odd byte length
>> ethernet packets).
>
> This is what the BLTBU and BLTUB instructions are for in the later microcode
> (converting between sensible PDP-10 memory and the mishmash you get as a
> result of DMA through the UBA to a 16-bit peripheral).  Since a DELUA is
> not 18-bit-data-aware, it ignores the high two bits of each 18-bit halfword
> when doing DMA.

That would be nice...

>> Is there some potential problem with regards to a PDP-11, which have two
>> parity bits for data, which are used for actual data on a KS? (If I
>> remember right.)
>
> IIRC you're OK as long as you don't set those bits in memory that the DELUA
> will read.  I feel like the Unibus documentation changed at some point,
> between whether PA/PB are actual parity bits (I think that's what the very
> early doc said), vs. being parity *error* bits (and I think PB isn't even
> really used -- PA asserted means there's been a parity error detected in the
> current DATI/DATIP).  I could be wrong about all of this.

I seem to remember having read that they were parity for each byte, but 
looking at a Unibus spec now (from 1979), it seems PB is actually 
indicating a parity error, while PA is reserved for future use. And the 
slave are expected to generate these signals, and the master is expected 
to check them, so I guess the DEUNA/DELUA should generate/check them, if 
it is a proper Unibus citizen. Which could make life in a KS interesting...

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol