Secondary floppy controller questions

[jrmymllr]

I have a P5 motherboard that of course supports two floppy drives, but I have a third I want to use. I'm an electronics DIYer so I built Sergey's Monster Floppy Controller, but populated only the secondary half, and the BIOS section. I know the floppy controller works because I used Maxtherabbit's floppy driver and could read a drive attached to it. The ultimate would be if I could also boot from a drive on this card (being able to boot from any of the three floppies in the system). I tried Sergey's multi floppy BIOS, but it just screws everything up and is unpredictable. To be fair, I don't believe it's for a system that already has its own floppy controller.

I was looking at some commercial floppy controllers with BIOS and noticed one states driver.sys must be used. So my question is, what good is the BIOS if I have to use a driver in DOS? Could an option ROM allow me to boot from a drive on a secondary controller? Or would this just not work? And could DOS ever directly detect and use a third floppy drive without a driver like it does with A: and B:? Or does the system BIOS have to support this?

 

[krebizfan]

DOS could detect a third floppy drive on the 5150 and 5160 (PC and XT) because those BIOSes were designed to permit 4 drives at once. Why IBM decided to limit the AT BIOS to only 2 floppy drives is a mystery to me.

I have to admit some puzzlement with the need to boot off any of three floppy drives. High density drives can boot off double density disks; the extra drive typically is a 5.25" DD to write double density disks. Could you describe the use case in more detail?

It is possible on some systems to boot off a floptical drive or SCSI floppy to extend the number of options though that generally only makes sense if the floppy controller is assigned unusual drives like 3.25" that don't exist in SCSI flavors.

 

[Chuck(G)]

In theory, it's possible to design a BIOS that boots from a secondary floppy, but I'm aware of none. The set of primary addresses/IRQs/DMA is firmly wired into a lot of software, so I'm not sure what good it would do.

Have you considered just switching the Drive Select/Motor enable lines on your primary to a third floppy? Some time ago, I posted on a card that I use with an AMD CPU board that supports only a single floppy.

 

[jrmymllr]

DOS could detect a third floppy drive on the 5150 and 5160 (PC and XT) because those BIOSes were designed to permit 4 drives at once. Why IBM decided to limit the AT BIOS to only 2 floppy drives is a mystery to me.

I have to admit some puzzlement with the need to boot off any of three floppy drives. High density drives can boot off double density disks; the extra drive typically is a 5.25" DD to write double density disks. Could you describe the use case in more detail?

It is possible on some systems to boot off a floptical drive or SCSI floppy to extend the number of options though that generally only makes sense if the floppy controller is assigned unusual drives like 3.25" that don't exist in SCSI flavors.

I'll admit it's a nice to have, but I have a 3.5 and 5.25, and a Gotek emulator to do most of the work because installing things with the Gotek is just far more convenient. But it would be nice to still have the capability to boot off the real floppy drives too. And I also like the floppy seek noise during POST

 

[jrmymllr]

In theory, it's possible to design a BIOS that boots from a secondary floppy, but I'm aware of none. The set of primary addresses/IRQs/DMA is firmly wired into a lot of software, so I'm not sure what good it would do.

Have you considered just switching the Drive Select/Motor enable lines on your primary to a third floppy? Some time ago, I posted on a card that I use with an AMD CPU board that supports only a single floppy.

I have seen this method of switching between drives, and that would be Ok. I do prefer each drive having its own dedicated interface though. This was the reason I asked you about that GSI card because interestingly, it has the same controller and same memory chip as the Monster Floppy controller (don't know if the same brand EEPROM though which could mean different commands for writes). I thought it would be interesting to try the BIOS image on it, but I can think of a few roadblocks I may encounter with that.

Which brought me to the question, if a floppy controller with BIOS doesn't allow one to boot from it, and won't get DOS to automatically detect and use it, what does it actually do? Because if a DOS driver is required anyway, that's where I'm at with the Monster Floppy controller, and it has no BIOS right now.

 

[maxtherabbit]

I was looking at some commercial floppy controllers with BIOS and noticed one states driver.sys must be used. So my question is, what good is the BIOS if I have to use a driver in DOS? Could an option ROM allow me to boot from a drive on a secondary controller? Or would this just not work? And could DOS ever directly detect and use a third floppy drive without a driver like it does with A: and B:? Or does the system BIOS have to support this?

I think you may be overestimating the weight and purpose of DRIVER.SYS. It doesn't even use 1kB of memory when loaded, and still relies on the option ROM or system BIOS to manage the drive. It's sole purpose it to inform DOS of the presence and type of additional floppy drive

 

[jrmymllr]

I think you may be overestimating the weight and purpose of DRIVER.SYS. It doesn't even use 1kB of memory when loaded, and still relies on the option ROM or system BIOS to manage the drive. It's sole purpose it to inform DOS of the presence and type of additional floppy drive

Ahh, ok I think that explains it. So your DOSFDRV.SYS does what the option ROM and DRIVER.SYS does. Sounds like I wouldn't be gaining much by screwing around with a BIOS on a card then since I likely won't get it to boot from that drive, and your driver does the rest that a ROM would normally handle.