Re: Cycle-accurate Floppy Disk emulation(82077AA)?
Posted on 2016-11-28, 22:59
Multitrack reads end at eot on side 1. They never read onto the next cylinder.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-28, 14:19
Unfortunately my documentation on the NEC µPD765 doesn't explain that behaviour:( http://www.isdaman.com/alsos/hardware/fdc/floppy.htm That's where you got the seek failed thing from, huh. You need to look at the datasheet for controller registers instead, http://www.classiccmp.org/dunfield/r/765. …
Re: IBM PC AT emulation crashing?
Posted on 2016-10-28, 02:20
Sure, it isn't documented anywhere but I ran headfirst into it and had to poke at the chip myself to find out what was happening.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-27, 22:07
The irq line is lowered when a byte is written to the command port. I've personally tested this with a real 765.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-27, 20:36
I've changed the setting of ST2 to 0x00 instead during seek to an invalid track. My latest source code: https://bitbucket.org/superfury/unipcemu/src/99f267f5cb8f160404d30e5a52746b733fa1871b/UniPCemu/hardware/floppy.c?at=master - Recalibrate always returns success, no matter what the floppy disk …
Re: IBM PC AT emulation crashing?
Posted on 2016-10-27, 18:54
PC FDCs never report drive not ready the as the ready line is forced set. Why are you setting bit 2 of ST2? That's scan failed not seek.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-27, 13:09
Oh, that's your code, I thought that was from bochs. If you look at bochs it only returns track 0 not found if the drive is missing or the motor is off (which was a mistake in my comment above as drives won't seek if not spinning). Made a error which reversed what I meant. So if there's no floppy …
Re: IBM PC AT emulation crashing?
Posted on 2016-10-27, 02:14
Oh, that's your code, I thought that was from bochs. If you look at bochs it doesn't return track 0 not found if the drive is missing or the motor is off (which was a mistake in my comment above as drives won't seek if not spinning).
Re: IBM PC AT emulation crashing?
Posted on 2016-10-26, 20:07
That error is only returned if there is no drive. The code comment even says it.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-26, 18:58
Recalibrate only returns track 0 not found if there is no drive connected. The command succeeds even if there is no disk.
Re: IBM PC AT emulation crashing?
Posted on 2016-10-25, 12:57
According to https://www.google.ch/patents/US5822778 the 80286 uses the FS and GS segments (just like the 80386), even though most documentations (like http://ref.x86asm.net/coder32.html#x65 ) mark the instructions prefixes as 80386+? I've modified the CPU core to use and allow the FS and GS …
Re: x86 Exceptions vs normal interrupts error code?
Posted on 2016-10-24, 13:52
I see no reason to think that double faults don't exist in real mode, after all you'd have to jump though hoops to even get one. As I said though, there's no docs one way or another and I'm fairly sure no one has actually tested it so you if you really want to know, you'll have to try it.
Re: x86 Exceptions vs normal interrupts error code?
Posted on 2016-10-23, 22:26
Most faults probably behave the same in real mode as protected mode except they're vectored though the IVT rather than the IDT but I could be wrong. Since these are minimally documented edge cases you'd have to actually test them on a real machine to know for sure.
Re: x86 Exceptions vs normal interrupts error code?
Posted on 2016-10-23, 19:58
#GP and #SP faults in real mode were not a concern of the 80286 designers. If a #GP fault arrives and the IRQ 5 handler that can't deal with the error code is invoked there's nothing that can be done about it. I'm sure Intel did lots of PC/XT software compatibility testing before releasing the 286. …
Re: x86 Exceptions vs normal interrupts error code?
Posted on 2016-10-23, 19:22
That's why they shouldn't do that. By keeping the interrupt gate DPL less than CPL for the interrupts that could also be faults the OS can make sure INT 00h-0Eh will cause a #GP fault rather than a software interrupt. Then just set the PIC to relocate the IRQs and do fix the DPL for them too. And …
Re: x86 Exceptions vs normal interrupts error code?
Posted on 2016-10-22, 20:23
The hardware will set the EXT bit if it's a external interrupt or a fault. Everything else is up to the software to figure out.
Re: DOSEMU in Windows?
Posted on 2016-10-22, 17:54
DOSEMU (and Wine for win16 support) require the ability to create LDT descriptors. Linux permits it in x86-64 mode but Windows doesn't. DOSEMU2 can use KVM so this might be possible to port with hyper-v paravirtualization. Edit: Looking back DOSEMU uses VM86 mode if available but can emulate the …
Re: IBM PC AT BIOS hangs on UniPCemu's 286 emulation?
Posted on 2016-09-29, 13:19
Edit: Tried changing that resulting value with no disk inserted giving a ST0 register value of 0x70 (Indicates: error, track 0 not found, Seek Ended). But the BIOS still gives errors about the floppy disk controller? Seeks shouldn't fail this way. The only time track 0 not found should be returned …
Re: IBM PC hardware clock division (XT 14MHz clock)?
Posted on 2016-08-28, 14:17
The Sound Blaster 1.0 uses a 12Mhz clock input to an 8051 timer (as mentioned above it's 12Mhz, I was thinking of an sb clone that has a 30mhz clock). The Sound Blaster 16 uses a 46.615120Mhz clock divided by (1024*256) and multiplied by a 8-bit value from a lookup table based on the desired …
Re: Properly emulating 80286+ multitasking protected mode with all exceptions etc.?
Posted on 2016-08-12, 12:42
Btw, if the address of the LIDT instruction exceeds the addressed segment and the double/#GP fault handler exists, won't it just be executed? Since the actual load has failed, the IDTR still has it's old(valid) value? Yes, this is why (assuming the idtr is valid) lidt -1 won't cause a triple fault. …
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