att6300p.cpp: Add support for 1.2MB drive (525hd)

[donohoe00]

The standard configurations for the 6300 Plus have drive A as a 1.2MB floppy, with either a hard drive or a 360K floppy as a secondary drive. One thing that's unique to the 6300 Plus is that port 0x65 is used for data rate control.

Since the FDC is on the motherboard, isa8_fdc_6300p_device is unique to the 6300 Plus... I'm wondering if it should go in a machine-specific file, instead of in fdc.cpp?

[rb6502]

I'd say just move this to the actual driver since it's on the motherboard. It's small enough that it can probably just go right in the driver, or you can add it as a separate device in mame/olivetti.

[donohoe00]

OK, I did the latter - should be good to go.

[rb6502]

Almost there. For motherboard devices added via a slot mechanism, you can use set_fixed() to prevent the user from changing them. For the most directly applicable example, the Kaypro 16 PC luggable in pc.cpp does this to lock down the ISA slots it uses:

subdevice<isa8_slot_device>("isa1")->set_fixed(true);

[donohoe00]

ISA8_SLOT(config, "mb2", 0, m_isabus, att6300p_mb_isa_devices, "fdc_6300p", true);

I thought that's what the last parameter was doing? If I change it to "false", I can change the device in the "Slot Devices" menu (well, it lets me choose between fdc_6300p or nothing, since there's only one option), otherwise the menu won't let me change it.