Re: [hatari-devel] ACSI emulation

2018-01-16 19:20 GMT+01:00 Nicolas Pomarède <npomarede@xxxxxxxxxxxx>:

Le 16/01/2018 à 00:52, Roger Burrows a écrit :

On 15 Jan 2018 at 23:29, Eero Tamminen wrote:

Hi,

On 01/15/2018 09:17 PM, Thomas Huth wrote:

On 15.01.2018 20:14, Roger Burrows wrote:

For EmuTOS-related reasons, I just measured the data transfer rate of an
emulated ACSI disk. On my not-very-fast Linux system, it's about 5 times

the

maximum rate observed on real hardware (6400kB/sec vs 1300kB/sec),

If Hatari should emulate something in this regards, I think it
should be interface speed, not some ancient storage medium.

This IS interface speed I'm talking about. Real disks may be slower.

According to Wikipedia, first SCSI standard (on which ACSI is based?),
has max speed of 5MB/s, and the SCSI chip in TT has max speed of
4MB/s:
https://en.wikipedia.org/wiki/SCSI#Parallel_SCSI
https://en.wikipedia.org/wiki/Atari_TT030#Technical_specifications

ACSI is only implemented on Atari systems, so the only relevant interface is on
real Atari hardware. If you can get I/O at over 1500KB/sec, you should tell
everyone how.

And the SCSI chip on the TT will not transfer at an effective rate above
2MB/sec.

I agree, Hatari should emulate DMA transfer at correct speed for acsi, not trying to match the real spec of asci/scsi, but taking into account the DMA transfer speed (this is what is already done for FDC accesses).

For example, the author of the demo "bad apple" released at sillyventure 2017 explained that during the dev he used Hatari, but when on the real machine the demo ran slower than expected because Hatari was too fast at transferring HD data :( So, he had to rework his transfer routines for real HW.

Nicolas

It would be nice if this could be adjustable (per ACSI/SCSI target), so different devices could be 'emulated' this way.

Semper Fidelis

Adam Klobukowski
adamklobukowski@xxxxxxxxx