Re: [MiNT] TT SCSI Speed (off topic)

[Michael Schwingen <rincewind@discworld.dascon.de>]

On Sun, Jun 20, 1999 at 12:18:13AM +1200, Mario Becroft wrote:
> As I am working on a SCSI - ethernet adapter, I have lately been
> implementing a SCSI target controller which I test on a standard,
> un-modified, 32 MHz TT. The controller is implemented in a FPGA (Field
> Programmable Gate Array). I have taken considerable effort to ensure that
> the controller is as fast as possible, and I believe I am achieving in the
> region of 95% to 100% of the maximum possible speed. Therefore by
> utilising this controller my results should represent the true maximum
> speed that is possible with the TT SCSI bus.

Just as a side note: the maximum transfer speed which I observed using
asynchronous SCSI was 4.8-4.9MB/s (using HowFast with block sizes
>>512bytes, which means overhead is nearly irrelevant) via GEMDOS, measured using a Fujitsu M2915 disk and a symbios
logic PCI controller in my Milan.

> Data transfer phase initiator from target (i.e. reading from SCSI
> peripheral): First byte takes an exceptionally long time (about 15
> microseconds) but subsequent bytes are transferred at a rate varying
> between approximately 1.9 and 2.0 megabytes per second.

IIRC, the TT transfers only data via DMA, so the CPU has to provide the
command data byte by byte - correct me if I am wrong.

cu
Michael
-- 
Michael Schwingen, Ahornstrasse 36, 52074 Aachen