exxos's Atari, Amiga & retro forum

Badwolf wrote: 26 Sep 2025 00:20

stephen_usher wrote: 26 Sep 2025 00:01 The other issue is that large block reads/writes would cause the system to hang in I/O wait for far too long for an interactive, multi-user, multi-tasking OS. Linux would most likely use the normal UNIX system 4K or, in exceptional cases, 8K chunks.

Interestingly the cursor continued to flash during my tests. Including when it hung, so interrupts must still have been working implying the bus isn’t relinquished for the entire duration of the transfer.

Does it work a bit like blitter nohog mode, I wonder?

Anyway point being I don’t see why multitasking would be unduly affected. Or perhaps I’ve misunderstood your point?

BW

exxos wrote: 26 Sep 2025 00:28 We need to know now if cubase has its own SCSI driver.. And if so.. Does it suffer from the same "8MB bug"..

These are the main changes in HDDRIVER 12.72:

- HDDRIVER: On the Falcon, an undocumented behavior of the DMA chip limits the number of bytes that can be transferred via SCSI/DMA in one go to just under 8 MiB. This value is also used by AHDI. The accelerated transfer mode for Ataris without Alternate-RAM has been adjusted accordingly.
- HDDRUTIL: The display of invalid partition data with "Check Boot Sector" has been improved.
- HDDRUTIL: Calling "Locate HDDRIVER" before an update installation could result in a corrupted HDDRIVER.SYS file. "Locate HDDRIVER" before an update is needless, because just like with the initial installation, double-clicking the boot drive is sufficient. The manual explains when to use "Locate HDDRIVER

Badwolf wrote: 25 Sep 2025 13:28 Here's how EmuTOS does it:

The sector count, calculated from file size and contiguous available clusters (1), is passed directly to the hardware and it's set off (2).

1. https://github.com/emutos/emutos/blob/m ... fsio.c#L84
2. https://github.com/emutos/emutos/blob/m ... csi.c#L167

So on a nice clean drive, a large file will be perhaps only three transfers depending on cluster boundaries (head, middle [the big bit], tail).

BW

Badwolf wrote: 26 Sep 2025 10:12 I note on the emutos-devel list it's reported that the 16k cluster limit is known about and enforced. I must have misinterpreted the trace I did above, in that case. I did however still see a lock up on Emutos PRG (albeit v1.3) so when I have a chance I'll investigate that further in case I was seeing an artefact of a previous (HDDriver-induced) failure.

one more thing I want to mention for the sake of completeness: The precise
limit is 8388096 bytes, not 16383 sectors. This is an important to memorize,
because media with a different physical sector size than 512 bytes also
have to be taken into account, and such media are also used by Ataris.
CDs or DVD-RAMs are a good example. If you are using software like ExtenDOS,
which uses the SCSI Driver, the block limit is 4096 sectors (blocks) for
data CDs and even less for audio CDs.
The same applies if you access a DVD-RAM disc, e.g. with a SATA drive
connected to the Atari. Almost any DVD-RW drive supports DVD-RAM media,
and HDDRIVER can make use of these media as if they were hard drives. You
can format them, partition them, and then use them with TOS.
A bit more exotic, but still in use with some Ataris: MODs. They also often
use physical sector sizes > 512 bytes.

czietz wrote: 26 Sep 2025 10:31 If you have a reproducible test case that shows that something still is wrong with EmuTOS's implementation, please share it on emutos-devel and Roger or I will have a look when time permits. However, I can confirm that the limit of 16383 for the Falcon SCSI DMA is known to EmuTOS and being enforced by its disk driver.

exxos wrote: 26 Sep 2025 11:48 one more thing I want to mention for the sake of completeness: The precise
limit is 8388096 bytes, not 16383 sectors. This is an important to memorize,
because media with a different physical sector size than 512 bytes also