Jason Thorpe wrote:

> On Tue, 16 Mar 1999 22:28:25 -0500 
>  Thor Lancelot Simon <tls@rek.tjls.com> wrote:
> 
>  > It seems to me the issue is quite probably not just that the TCDS card is
>  > on a 12.5MHz TurboChannel bus, it's also that, as mentioned above, it
>  > can't DMA directly to/from host memory -- everything has to be copied to
>  > a buffer on the card first.  That's burning a lot of memory bandwidth and
>  > CPU cycles on a machine that's not exactly got a whole lot of either to
>  > spare...
> 
> Um... the TCDS certainly CAN DMA to host memory.  It's the PMAZ-A
> which cannot (TURBOchannel single scsi).  Those the CPU must bounce
> the data to/from the SRAM buffer on the card.
> 
>  > I think Jonathan and I discussed a couple of times whether it was feasible
>  > to put one of the TurboChannel SCSI cards that shipped with the Alphas --
>  > which *could* DMA directly to/from host memory -- into a TC DECstation.
>  > AFAIK nobody has mashed the appropriate device drivers into shape and tried
>  > it yet.
> 
> That' the TCDS (TURBOchannel Dual SCSI), and Tohru has made the driver
> work on the DECstation.  He's sent some mail about this before, as I
> recall...
> 
> So, anyhow, it seems perfectly reasonable that the TCDS is eing
> limited by the 12.5MHz TURBOchannel.

Note that the 5000/2xx series machine have a 25MHz
TURBOchannel, unlike the /xx and /1xx machines have.

Some figures for "time dd if=/dev/rrzXc of=/dev/null bs=32k count=32k".
All disks are RZ28Ms.

5000/240  NetBSD 1.3.3  onboard SCSI	0.598u 31.750s 4:44.83 11.3%  3.60 MB/s
5000/240  NetBSD 1.3.3  T/C SCSI	0.851u 30.421s 7:17.81  7.1%  2.34 MB/s
5000/260  NetBSD 1.3K   onboard SCSI	0.392u 13.416s 4:19.68  5.3%  3.94 MB/s
5000/260  Ultrix 4.5    onboard SCSI	0.855u 10.307s 5:42.74  3.2%  2.99 MB/s
5000/260  Ultrix 4.5    T/C SCSI	0.703u 11.878s 5:45.86  3.6%  2.96 MB/s

Given that TURBOchannel is a 32bit bus, you'd think that a 25MHz bus
with a peak bandwidth of 100Mbyte/s could sustain more than the 5MB/s we
can get out of narrow 8bit SCSI.  Ultrix's figures of almost identical
figures for onboard and T/C give some hope of getting better figures for
NetBSD's T/C SCSI performance.

As far as part numbers, Ultrix's tc_option_data.c lists a PMAZ-AA as an
"asc" board and "PMAZB-AA" and "PMAZC-AA" as using the "tcds" driver.
The on-board controller probes as a "PMAZ-BA" under Ultrix.

Simon.