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Home Forums 68kMLA Calling Lisa gurus: Floppy Emu disk emulation — #15
Post #15 by bigmessowires
Source Forum68kMLA
CategoryTroubleshooting
Post DateTue, 24 Feb 2015 - 04:04
Original URLhttps://68kmla.org/bb/threads/calling-lisa-gurus-floppy-emu-disk-emulation.1329/
Post
I posted a longer progress update at http://www.bigmessowires.com/2015/02/23/lassoing-the-lisa/, as well as a link to the new firmware I'm using. If anyone else has a Lisa and a Floppy Emu and wants to try this out, please read that update and then grab the firmware from the link at the end.

The good thing that may come out of this is you'll discover bugs that you never even knew you had! (as youve noticed) and ultimately increase performance on the Macintosh. 
Yeah! I hope so. Normally the Floppy Emu seems well behaved, but I have noticed a few test cases with specific machine and OS combinations where it sometimes seems to do a LARGE number of retries. So maybe this is the explanation.

is the data rate on the Lisa's drive interface slightly different than on the Mac? It talks about initializing the... whatever, at either "15.7mhz" or "16mhz";...

my thought there was that the PWM signal from the Lisa might spin the drive slightly faster than it does in the Mac to make it even, but then it occurred to me that the Lisa can supposedly work with 800k drives that ignore PWM with an upgrade so... yeah, never mind that idea.)
Great thought. Though I don't think that's a factor here, I could be wrong. On the Mac, the IWM works at one bit per 16 clock cycles, and with a 7.8336 MHz clock, that comes to one bit every 2.04 microseconds. On the Lisa, I think it's precisely 8 MHz (or 16 MHz???), so that comes to one bit every 2 microseconds. Floppy Emu already runs at exactly 2 microseconds per bit, so if anything it should be better on the Lisa than on a Mac. And Floppy Emu ignores the PWM signal, same as how an 800k drive does.

Using my Floppy Emu, SN#67, App FW 1.0 L, CLPD FW 11
That is awesome! And perplexing. 1.0L-FW11 is a slightly older firmware, so it's possible that some change I made afterwards actually broke the emulation from the point of view of a Lisa. Or maybe the firmware is immaterial, and there's some different about your Lisas. Do you know if they have an 800K ROM on the IO board?

But what's really strange is that 1.0L-FW11 still contains the bitslip generation bug that I mentioned. So if your tests worked (albeit slowly), it means that bitslip wasn't actually the source of the problems I was having. It might still be a bug, but probably not THE bug. Or maybe there are several bugs, all interacting with each other.

mp.ls