I'm starting to finally add various Tube devices to the BBC Micro range. These are 2nd processors that can be added and the official Acorn devices include 6502, 65C102, Z80, 32016, 80186, 80286, ARM. They (parasite) communicate with the BBC Micro (host) via a Tube ULA (Ferranti and later Acorn). The Tube ULA is fairly well documented and I've added this as a new machine device (tube). When working we'll be able to promote some machines to working bbcmt, bbcm512 and support the currently not supported software lists bbc_flop_6502, bbc_flop_z80, etc.
So far I have 6502 and almost 65C102 working, just need to check interrupts are fully handled between host and parasite CPU's.
6502 2nd Processor:
The Z80 is in progress but I'll come back to that later.
I need a little advice on the 80186. The Tube device has 8 registers to be addressed from the parasite CPU. The 8-bit CPU's map these consecutively so I have handlers parasite_r, parasite_w and for the Z80 are addressed:
static ADDRESS_MAP_START(tube_z80_io, AS_IO, 8, bbc_tube_z80_device)
AM_RANGE(0x00, 0x07) AM_DEVREADWRITE("ula", tube_device, parasite_r, parasite_w)
For the 80186 the registers are mapped into even locations only:
static ADDRESS_MAP_START(tube_x86_io, AS_IO, 16, bbc_tube_80186_device)
AM_RANGE(0x80, 0x8e) AM_DEVREADWRITE8("ula", tube_device, parasite_r, parasite_w, 0x00ff)
Is there a way to map my 8 registers into even locations only, ie. 0x80, 0x82, 0x84, 0x86, 0x88, 0x8a, 0x8c, 0x8e. Or should I just create another set of handlers in my tube_device, parasite_x86_r, parasite_x86_w?
The 80186 co-processor has 512K RAM and 16K ROM and memory map is:
00000h to 3FFFFh : Lower 256kb of RAM
40000h to 7FFFFh : Upper 256kb of RAM
80000h to BFFFFh : Upper 256kb of RAM
C0000h to FFFFFh : ROM
My address map for this is:
static ADDRESS_MAP_START(tube_x86_mem, AS_PROGRAM, 16, bbc_tube_80186_device)
AM_RANGE(0x00000, 0x3ffff) AM_RAM
AM_RANGE(0x40000, 0x7ffff) AM_RAM AM_MIRROR(0x80000)
AM_RANGE(0xc0000, 0xc3fff) AM_ROM AM_REGION("bootstrap", 0) AM_MIRROR(0x3c000)
But am unsure of my AM_MIRROR's and when run I don't see my bootstrap region anywhere in memory, am expecting to see it mirrored throughout c0000-fffff.