An UZI target for the Amstrad PCW series computers

16K banked memory with flexible bank setting. Programs for now (until brk()
is done right) get 64K in four consecutive page numbers. The UAREA is mapped
high at 0xF900 with the process and irq stacks following and a copy of the
common area beyond (so we have a sort of common code area as needed)

The very top of memory must be free as the top of bank 3 (top of OS kernel
mapping) is "magically" the keyboard mappings.

Need to try and keep kernel under 48K or so to make it easier to handle the
screen memory, fonts etc. We need to put the screen (720x256 pixels + roller
ram table of 512 bytes or so = ~ 24K) in the low 128K

WIP - lots to do to add swap support and memory map needs a re-arrange so we
can get fork() going

FIXME:
- Move disk buffers into own bank and use external disk buffers to keep under
  the 48K line


Supported Hardware (all only in early test)
------------------

	Amstrad PCW 8256
	Amstrad PCW 8512
	Joyce emulation of the above

	Planned:
	Amstrad PCW 9256/9256+/9512/9512+/PCW10 (need a subtly different boot
		disk)

	Options:
		CF2 floppy
		CF2DD floppy
		3.5" floppy	(need to sort seek rates better)
		UIDE
		Fake IDE on xjoyce
		CPS8256 and clones (parallel port not yet done)
		AMX mouse
		Kempston Mouse
		Kempston Joystick

	Planned:
		Keyboard mouse/joystick hacks
		Centronics on CPS8256
		Standalone centronics
		DKTronics sound

	Not Supported:
		Other printers
		SCA Mark2 RTC
		Locolink
		Other hard disk controllers



Building A Boot Image
---------------------

edit Makefile and set it to z80, platform pcw8256
make clean; make
cd platform-pcw8256/BOOTBLOCK
zmac 765.s


# Make a blank disc
dd if=/dev/zero of=bootdisk.raw bs=512 count=360
# Add the boot block in sector 0
dd if=platform-pcw8256/BOOBLOCK/765.cim of=bootdisk.raw conv=notrunc
# Add the kernel
dd if=fuzix.bin of=bootdisk.raw bs=512 seek=1 conv=notrunc

# Start the emulator
xjoyce

Hit F3 (Boot from alternative disc)
Boot From
	=>Other
Enter filename for disc image
	Disc file...
		select bootdisk.raw
	Advanced
		Raw disc image file
	OK
	OK

Should boot and detect the drives then prompt bootdev:

At that point the keyboard should work.

The floppy driver is incomplete but given a rootfs image on /dev/fd1 you
should be able to at least get it to mount

device 256 = fd0 257 = fd1

(0-255 are the UIDE hard disks, or FID hard disks on Joyce)


Mixed boot/root images are not currently supported (this just needs a modified
boot block that starts at a different offset)


Memory
------

Then PCW8256 memory is split into multiple banks not all of which can be used
for any purpose

The display takes 23040 bytes of video line memory. Each line must be within
the low 128K and is indexed by the roller RAM

The roller RAM must also be within the low 128K and is 512 bytes.

The keyboard magically replaces the top 16 bytes of bank 3.

Our loader puts the screen into bank 4 and bank 5 (part of), then loads the
OS into bank 0/1/2/3.

Other work needed here is to put the buffer cache at the end followed by the
font data if we do it this way, then discard. At that point we can move the
font into video mappings.

Right now bank 0-3 are fully used if we do the buffer reclaim (which gets us
a nice 12 or so extra buffers), bank 4 is all video and bank 5 would have
5K left after the fonts.  An obvious use for that would be to go to 256
byte tty queues and add ptys - (costing us about 3K)

Other candidates would be the low level graphics rendering routines as we'll
want those for a graphics mode (or we need to support an mmap like mode for
direct mapping a 16K graphics window over the app memory)