Amiga questions you've always been too embarrassed to ask

[dJOS]

Originally Posted by s2325

Why there is information about both sides when you don't need to swap? http://hol.abime.net/1385/diskscan

That really is bizarre considering 3.5" floppy disks are physically incapable of being flipped due to the physical design of the floppy case.

It's physically keyed in multiple areas to prevent being inserted upside down and on top of that the metal drive coupling is on the underside of the disk so it physically can't be spun up if upside down. Adding to that the shutter only opens in one direction.

[Amiga1992]

Originally Posted by dJOS

That really is bizarre considering 3.5" floppy disks are physically incapable of being flipped due to the physical design of the floppy case.

It's still double sided disks. Remember? 2SDD, Double Sided, Double Density.

You don't need to flip a disk to access both sides, the drive head, if I am not wrong, can read from both sides. As DisposableHero said, this is pointless to the user though.
Amiga disks have 79 tracks per side.

If I am not wrong, the 1571 C= disk drive was also double sided so you could read both sides of a floppy without flipping the disk, if in 1571 mode. Anybody correct me if I am wrong please.

[thomas]

Originally Posted by Akira

Amiga disks have 79 tracks per side.

80 tracks numbered from 0 to 79.

2 * 80 * 11 * 512 = 901120 = 880 * 1024

[dJOS]

Originally Posted by Akira

It's still double sided disks. Remember? 2SDD, Double Sided, Double Density.

You don't need to flip a disk to access both sides, the drive head, if I am not wrong, can read from both sides. As DisposableHero said, this is pointless to the user though.
Amiga disks have 79 tracks per side.

If I am not wrong, the 1571 C= disk drive was also double sided so you could read both sides of a floppy without flipping the disk, if in 1571 mode. Anybody correct me if I am wrong please.

I think you missed the point, the label on the 3.5" disk instructs you to flip it, even with Atari 520st single sided drives, this it's physically impossible.

[Samurai_Crow]

Originally Posted by Akira

It's still double sided disks. Remember? 2SDD, Double Sided, Double Density.

You don't need to flip a disk to access both sides, the drive head, if I am not wrong, can read from both sides. As DisposableHero said, this is pointless to the user though.
Amiga disks have 79 tracks per side.

If I am not wrong, the 1571 C= disk drive was also double sided so you could read both sides of a floppy without flipping the disk, if in 1571 mode. Anybody correct me if I am wrong please.

The 1571 could read both sides of a 1571 disk. If someone clipped a notch out of the disk and formatted it single sided on both sides, the second side would have to spin backwards to read it without flipping it.

[Amiga1992]

Originally Posted by dJOS

I think you missed the point, the label on the 3.5" disk instructs you to flip it, even with Atari 520st single sided drives, this it's physically impossible.

No I didn't, I was saying that the floppy still has "two sides" hence the confusion by the computer illiterate designer.

[Daedalus]

Originally Posted by Akira

So basically, there are TWO ways to read multiple buttons on an Amiga joystick port, and you cannot have code that supports both at the same time. I'm not exactly sure why these adapters don't work, what I can guess is that many of these ports use WHDLoad slaves and those slaves are usually made with Master System or Genesis code in them for a 2 button joystick.

The Amiga (and any other system using the Atari 9-pin controller connections) can only read up to 3 buttons without needing to resort to tricks. Once you do that, you need to repurpose some of the signals in order to let the system look at the different buttons independently. Almost every system with more buttons than I/O pins does this differently. Some use a sort of bank switching (like the Megadrive/Genesis), where the system outputs a signal enabling one or other sets of buttons, then reading them in over the remaining pins. Others use a serial input (like the SNES), where each button is assigned one bit, and a clock signal from the computer keeps everything in sync while all controls are read in over one pin. The CD32 uses a serial input combined with the traditional joystick scheme, and a mode selector, so directions are controlled by their original pins but serial is used for the buttons. The clock and selector signal used for the communication are on the same pins as the original fire buttons, so the software must decide to use one or the other. It can't do both.

[Twiggy]

That's pretty damn interesting. Shame it means I need hunt around for some CD32 controllers that work with the unofficial compilations. That or make my own WHDload compilations.

[Mrs Beanbag]

CD32 wasn't released until late 1993, by which time some games already existed that used Master System style two-button joysticks, so why C= opted for the serial-data version instead of something more like the Megadrive (which would have been much simpler to implement (?) imho, while retaining compatibility), i dunno... these decisions are made by somebody somehow, there is presumably a reason.

I have been meaning for ages to make an adapter to enable Megadrive pads to be fully programmable on Amiga, which is possible in theory i think, by swapping two pins over, it would make far more pads available, if it worked, but of course no existing games would use it.

[idrougge]

Originally Posted by Mrs Beanbag

I have been meaning for ages to make an adapter to enable Megadrive pads to be fully programmable on Amiga, which is possible in theory i think, by swapping two pins over, it would make far more pads available, if it worked, but of course no existing games would use it.

Except Flashback.

[Daedalus]

Originally Posted by Mrs Beanbag

CD32 wasn't released until late 1993, by which time some games already existed that used Master System style two-button joysticks, so why C= opted for the serial-data version instead of something more like the Megadrive (which would have been much simpler to implement (?) imho, while retaining compatibility), i dunno... these decisions are made by somebody somehow, there is presumably a reason.

The Amiga has supported 3 buttons since launch but nobody ever used them. And while the serial protocol is a little more complex than a Megadrive controller, it's not a huge difference really and either type would still needs games to be written specifically to take advantage. It also has the advantage that controller type is detectable by software, something that can never be done for a MD pad. It does offer backwards compatibility as well - it works as a standard 2-button controller for non-CD32 games, just as the Mastersystem pad does. I'm not sure what the problem with compatibility you're referring to might be.

I have been meaning for ages to make an adapter to enable Megadrive pads to be fully programmable on Amiga, which is possible in theory i think, by swapping two pins over, it would make far more pads available, if it worked, but of course no existing games would use it.

Yep, only the one game I can think of as idrougge has pointed out. It's trivial to add support for it in newer games however. All that's needed is for pins 5 and 7 to be swapped, then toggle pin 5 to switch between the two banks of buttons to read them.

[Mrs Beanbag]

Originally Posted by Daedalus

It also has the advantage that controller type is detectable by software, something that can never be done for a MD pad. It does offer backwards compatibility as well - it works as a standard 2-button controller for non-CD32 games, just as the Mastersystem pad does. I'm not sure what the problem with compatibility you're referring to might be.

ok i must have confused myself somehow then, you said "The CD32 uses a serial input combined with the traditional joystick scheme, and a mode selector" so if two lines are already used for "serial input" and "mode selector" then how are there enough lines left for two buttons? I have obviously not understood this correctly.

Yep, only the one game I can think of as idrougge has pointed out. It's trivial to add support for it in newer games however. All that's needed is for pins 5 and 7 to be swapped, then toggle pin 5 to switch between the two banks of buttons to read them.

i did not know that about Flashback, that is very interesting, is such an adapter actually available anywhere or am i going to have to get the soldering iron out like i originally planned?

[Amiga1992]

Originally Posted by Mrs Beanbag

i did not know that about Flashback, that is very interesting, is such an adapter actually available anywhere or am i going to have to get the soldering iron out like i originally planned?

THere's no adapter like that, afaik Flashback docs came with a description of how to make your own adapter.

[Daedalus]

Originally Posted by Mrs Beanbag

ok i must have confused myself somehow then, you said "The CD32 uses a serial input combined with the traditional joystick scheme, and a mode selector" so if two lines are already used for "serial input" and "mode selector" then how are there enough lines left for two buttons? I have obviously not understood this correctly.

Umm, well maybe I didn't describe it well enough. On a joystick port you can have 3 buttons *or* CD32 mode, not both. The CD32 provides the four directions straight up as a traditional joystick, and then can either give two fire buttons on the standard fire 1 & 2 pins (classic mode), or serial input for all buttons (CD32 mode). In CD32 mode it doesn't transmit any fire buttons on the standard pins at all, those pins are re-used for the serial transfer. The third fire pin is used by CD32 games as the mode select output to put the pad in CD32 mode, and is the same signal used with a MD adaptor to read the extra buttons.

i did not know that about Flashback, that is very interesting, is such an adapter actually available anywhere or am i going to have to get the soldering iron out like i originally planned?

I've never seen a commercial one, though homebrew ones show up on eBay, AmiBay and the likes from time to time. I've built one myself including diodes to protect a C64 should I ever use it with one. They're pretty trivial to build as you'd expect, so get the soldering iron out

[Mrs Beanbag]

ah ok i get it, so it is compatible by having a "compatibility mode" whereas MD format is simply an extension of the original spec making use of the remaining unused pin, i think i prefer the MD's way, personally, but then they needed even more buttons than that and the way the 6-button Megadrive pads worked was quite crazy.

I would like to support Megadrive pad in future games.

[Daedalus]

Yep the MD way is simpler alright, and the 6-button pad is another thing again. I don't have one but from what I remember it sends the extra button signals on the D-pad lines on the trailing edge of the bank switch signal. Seems funky to me when they could've squeezed them into the original protocol but I guess they had their reasons - maybe certain game compatibility or something. Whatever their reasons were for changing the power pin though, it was a bizarre decision.

As for the CD32 pad, yep it's a compatibility mode, but it's also the default mode, meaning it should work with any game that uses a 1 or 2-button pad.

[Amiga1992]

Originally Posted by Daedalus

meaning it should work with any game that uses a 1 or 2-button pad.

As long as they support a 2 button MASTER SYSTEM pad. I have to say again that games coded to work with Megadrive pads don't work with Master System pads (example: Alien Breed: TA). The way the second button is read is different. First button will work fine.

[Mrs Beanbag]

Originally Posted by Daedalus

Yep the MD way is simpler alright, and the 6-button pad is another thing again. I don't have one but from what I remember it sends the extra button signals on the D-pad lines on the trailing edge of the bank switch signal.

i thought they just pulsed the Select line with a short pulse (instead of holding the signal) to select the third bank?

Whatever their reasons were for changing the power pin though, it was a bizarre decision.

yeah that was quite strange, given it was a fairly established standard already, that they were already using in their consoles..

Originally Posted by Akira

As long as they support a 2 button MASTER SYSTEM pad. I have to say again that games coded to work with Megadrive pads don't work with Master System pads (example: Alien Breed: TA). The way the second button is read is different. First button will work fine.

Hm! shouldn't be, AFAIK...

Pin 6 = Button 1 or Button B
Pin 9 = Button 2 or Button C, if Select is high (which it should be)
if Select is low on a MD pad, Button B becomes Button A and Button C becomes start.

Why they didn't just multiplex the D-pad to get more buttons for the 6 button pads i don't know, it would have been simple but perhaps it broke some games, that expected Up and Down to still work with Select line low?

[Amiga1992]

We discussed this at length here:
http://eab.abime.net/showthread.php?t=81330
On page 3 we discuss AB:TA vs. AB2 (AB2 works with SMS pads, not with MD pads, AB:TA works with MD pads)

The fact is: games that support the SMS pad 2 button don't work with the MD pad C button (dunno about viceversa, gotta check but I don't have an SMS pad now) and it seems to have to do with this question of what pin is pulled high or not or whatever. I am not techy enough to explain it though :/ Daedalus gave some insight again over there.

[Mrs Beanbag]

hm! that is very odd, mind you it is not entirely straightforward even to read the second button in software on the Amiga. Reading the first button it is just a bit in a register, to read the second button is a bit more involved, it is because of the circuitry for reading analogue joysticks i think, you have to set a bit, wait, and then read it back. So maybe that whole process confuses things.