[cctalk] Re: emulating floppies [was: Paper tape in casettes...]
CORRECTION: GCR was used on Apple2, 400K/800K Mac, Commodore, Sirius/Vector, etc. That should read Victor 9000, NOT Vector [Graphics] Vector Graphics was hard sectored, and not GCR. Northstar is probably the best known of the hard sector formats.
[cctalk] Re: emulating floppies [was: Paper tape in casettes...]
On Tue, 27 Feb 2024, CAREY SCHUG via cctalk wrote: did not know about gcr/mfm on same floppy...if you respond, please mention who does that. gaak, I don't even recognize "gcr" at this point. I remember mfm and something else. mfm was single density, right? was gcr double density? does not seem familiar, but certainly there was a double density encoding scheme that the device attached to the floppy cable would have to recognize. Grossly oversimplified: FM is Frequency Modulation, often called "single density". There are clock pulses, and bit or no bit between the pulses, therefore, strings of off bits look like one frewuency, and strings of on bits look like another (double) frequency. MFM is Modified Frequency modulation. when it came out, it was almost double the capacity of FM, so the marketing people called it "double density". It wasn't until after that naming that FM began to be called "single density" (In a very similar way, if you look at old newspapers, "World War 1" wasn't called that until the existence or spectre of "World War 2") It was obvious that clock pulses weren't really needed between on bits. By leaving those ones out, the average frequency/signal density was much lower, making it possible to increase (typically double) the data transfer rate. and thus almost twice the capacity per track. GCR is Group Coded Record. Some patterns of bits are more "spread out" than others. If you can find those, you could break up your 8 bit data into 2 "nybbles" of 4 bits each, using only the nybbles that were spread out enough to increase the data transfer rate, and squeeze more of those pairs into the space that the 8 bit bytes had taken. If you can find 32 "loose" patterns, then you could record 5 bytes into 8 of those patterns. A little extra firmware to do the conversion, but nothing horrendous. Thus GCR typically would be about one and a half as much data per track as FM, GCR was used on Apple2, 400K/800K Mac, Commodore, Sirius/Vector, etc. 1.4M Mac is ordinary MFM, and can be done with WD style disk controllers. Commodore Amiga was MFM, BUT, did not have the IBM/WD track and sector structures; losing those, and reading a track at a time, and decoding that into sectors in software permitted a little more capacity per track/disk. In addition, on some hard drives, RLL (Run Length limited) is similar to GCR. Changing the motor speed or the data transfer rate for different tracks, makes it easier to use different numbers of sectors, to put less data on the small inner tracks, and more on the longer outer tracks. In order to get closer to a standard linear velocity on the track, instead of a standard angular velocity. There are a few machines, such as Ensoniq, that would put multiple sizes of sectors on a track! You can fit 5 1024 byte sectors on a track, but not enough left for a sixth; however there was enough space for an additional 512 byte sector. There were more recording formats, such as MMFM, having FM sector headers, with MFM sector content, etc. The NEC 765 and its ilk are similar to WD 179x in capability, but with important differences, including, WD has a "track read" command, NEC does not but has a "multiple sector resd", NEC is "flash blinded" by the index pulse, and needs a little more time after index before reading, some NEC controllers can't handle 128 byte MFM sector, many are implemented without support for FM on the FDC board, . . . -- Grumpy Ol' Fred ci...@xenosoft.com
[cctalk] Re: emulating floppies [was: Paper tape in casettes...]
On 2/27/24 15:43, Wayne S via cctalk wrote: > I know you do this for a living and are good at it. Most of us don’t do it as > a living but have piles of floppies that we want to recover cheaply using an > existing method. Grease, cat and other wezels, are fine but you have to do > more work to get usable stuff, unless your floppies are all c64 The > applesauce just seems further along than the others. > Just my opinion. To be fair, the OP was talking about replacing the WD disk controller. As far as I know, WD 17xx and 27xx controllers can do FM and MFM. Heck, they can't even do M2FM. A small exception. Back in the 1970s, we did do GCR using the WD1781, which is basically a 1771 without the modulation appendages. And even then, it took a Multibus-sized board to implement the scheme. --Chuck
[cctalk] Re: emulating floppies [was: Paper tape in casettes...]
Vector uses gcr. Apparently. I’m not well versed in any of this, just relaying stuff i read from the Applesauce discord support channel. People ask questions like all of yours there all the time. Join it and scroll back on that channel. Lotsa interesting stuff. Sent from my iPhone > On Feb 27, 2024, at 15:43, Wayne S wrote: > > I know you do this for a living and are good at it. Most of us don’t do it > as a living but have piles of floppies that we want to recover cheaply using > an existing method. Grease, cat and other wezels, are fine but you have to > do more work to get usable stuff, unless your floppies are all c64 The > applesauce just seems further along than the others. > Just my opinion. > > Sent from my iPhone > >> On Feb 27, 2024, at 15:33, CAREY SCHUG via cctalk >> wrote: >> >> I knew most of this, which is why emulating the floppy controller should be >> easier. >> >> applesauce is platform specific (ok, ANY floppy emulation will be platform >> specific for apple) >> >> I thought the applesauce page said it was not yet available for standard >> shugart style as in trs-80, s-100... >> >> greaseweasel is platform specific. the color coco is not yet available in >> the USA, needing shipping from Europe, which in my experience is not cheap. >> not even promised for trs80 1/3/4 or s-100. and are the parts cheap? dunno. >> >> did not know about gcr/mfm on same floppy...if you respond, please mention >> who does that. gaak, I don't even >> recognize "gcr" at this point. I remember mfm and something else. mfm was >> single density, right? was gcr >> double density? does not seem familiar, but certainly there was a double >> density encoding scheme that the >> device attached to the floppy cable would have to recognize. >> >> I had forgotten that atari? commodore? changed speed, though I remember I >> knew that before. >> >> --Carey >> On 02/27/2024 5:18 PM CST Wayne S via cctalk wrote: >>> >>> >>> The “support” channel has the most info on the applesause. >>> >>> >>> Sent from my iPhone >>> On Feb 27, 2024, at 15:12, Wayne S wrote: >>> >>> Chuck, not to disagree much, because you are an expert, but there’s more >>> to decoding floppies than just reading them. Some floppies have tracks that >>> are recorded at different speeds. Some have tracks that use different >>> modulation gcr on some and mfm on others. A lot of floppies have different >>> skew. The applesauce tries to handle these problems and give you a readable >>> file. It’s mostly in the software. >>> >>> I tried to send the discord link but don’t know if it got thru so here it >>> is again >>> >>> https://discord.gg/njetE8zU >>> >>> Wayne >>> >>> >>> Sent from my iPhone >>> On Feb 27, 2024, at 15:02, Chuck Guzis via cctalk wrote: >>> >>> On 2/27/24 14:42, Wayne S via cctalk wrote: >>> Take a look at the Applesauce. >>> It hooks up to a lot of different floppy drives and records and decodes the >>> flux. >>> Version2 of the hardware is being sourced and should be available in a few >>> months. >>> >>> Good grief, there are more of these things floating around than one can >>> shake a stick at. The Greasweazel is perhaps the cheapest, using a $3 >>> ($1.30 or so from Aliexpress) STM32F103 "Blue Pill" board. >>> >>> It's almost trivial doing this if you don't need the "eye candy". >>> Basically you run a timer in capture mode, with capture triggered by an >>> edge on the drive's "read data" line. >>> >>> Modern MCUs don't even break a sweat doing this. >>> >>> It's nice seeing the proliferation after many years of harping on the >>> subject... >>> >>> --Chuck
[cctalk] Re: emulating floppies [was: Paper tape in casettes...]
I know you do this for a living and are good at it. Most of us don’t do it as a living but have piles of floppies that we want to recover cheaply using an existing method. Grease, cat and other wezels, are fine but you have to do more work to get usable stuff, unless your floppies are all c64 The applesauce just seems further along than the others. Just my opinion. Sent from my iPhone > On Feb 27, 2024, at 15:33, CAREY SCHUG via cctalk > wrote: > > I knew most of this, which is why emulating the floppy controller should be > easier. > > applesauce is platform specific (ok, ANY floppy emulation will be platform > specific for apple) > > I thought the applesauce page said it was not yet available for standard > shugart style as in trs-80, s-100... > > greaseweasel is platform specific. the color coco is not yet available in > the USA, needing shipping from Europe, which in my experience is not cheap. > not even promised for trs80 1/3/4 or s-100. and are the parts cheap? dunno. > > did not know about gcr/mfm on same floppy...if you respond, please mention > who does that. gaak, I don't even > recognize "gcr" at this point. I remember mfm and something else. mfm was > single density, right? was gcr > double density? does not seem familiar, but certainly there was a double > density encoding scheme that the > device attached to the floppy cable would have to recognize. > > I had forgotten that atari? commodore? changed speed, though I remember I > knew that before. > > --Carey > >> On 02/27/2024 5:18 PM CST Wayne S via cctalk wrote: >> >> >> The “support” channel has the most info on the applesause. >> >> >> Sent from my iPhone >> >> On Feb 27, 2024, at 15:12, Wayne S wrote: >> >> Chuck, not to disagree much, because you are an expert, but there’s more >> to decoding floppies than just reading them. Some floppies have tracks that >> are recorded at different speeds. Some have tracks that use different >> modulation gcr on some and mfm on others. A lot of floppies have different >> skew. The applesauce tries to handle these problems and give you a readable >> file. It’s mostly in the software. >> >> I tried to send the discord link but don’t know if it got thru so here it is >> again >> >> https://discord.gg/njetE8zU >> >> Wayne >> >> >> Sent from my iPhone >> >> On Feb 27, 2024, at 15:02, Chuck Guzis via cctalk >> wrote: >> >> On 2/27/24 14:42, Wayne S via cctalk wrote: >> Take a look at the Applesauce. >> It hooks up to a lot of different floppy drives and records and decodes the >> flux. >> Version2 of the hardware is being sourced and should be available in a few >> months. >> >> Good grief, there are more of these things floating around than one can >> shake a stick at. The Greasweazel is perhaps the cheapest, using a $3 >> ($1.30 or so from Aliexpress) STM32F103 "Blue Pill" board. >> >> It's almost trivial doing this if you don't need the "eye candy". >> Basically you run a timer in capture mode, with capture triggered by an >> edge on the drive's "read data" line. >> >> Modern MCUs don't even break a sweat doing this. >> >> It's nice seeing the proliferation after many years of harping on the >> subject... >> >> --Chuck
