Hu7 development system interface routines

[ccovell]

Hi, folks.  The talk about NEC Avenue games having analogue joystick code in them, etc, got me browsing around a few of their ROMs.  And I found something cool inside the boot bank of OutRun (probably others...): from $F400- onwards, it has a minimal Hu7 command interface!

Search around for the Hu7, Hu7CD on the Web or YouTube if you don't have an idea of it yet.  It contains a large amount of extra RAM, and possibly several MBits of ROM space too.  Well, by examining how the OutRun code does stuff, we can glean a bit of information about the Hu7 interface.

At least bank $FC contains RAM, and it is needed as OutRun's code copies bank $00 to this, then modifies the first $400 bytes, and uses it as a boot bank as well as RAM.

A PC Parallel Port is connected to the Hu7 system, and its ports are $1C00-1C4x or higher.  These ports are always accessed by the PC-Engine in LOW CPU SPEED MODE...

A map of ports:
$1C00: data byte from PC to PCE
$1C01: data byte to PC from PCE
$1C02: handshake from PC to PCE in bit 2 and/or 3
$1C03: handshake to PC from PCE in bits 0,1,3,4, and 7 (dunno what they all do)
$1C20-$1C22:  (??  CD-ROM simulator?)
$1C40: ?  Both written and read.

Dunno about the others for now, but the command interpreter in OutRun waits for the bytes $48,$75,<command byte> then acts on command numbers from $00-$1F.  (Heartwarmingly, $48,$75 is "Hu" in ASCII.)

The commands (as far as I have deciphered them) are:
00: "NO COMMAND"
01: Send byte data "$03,$11" to PC from PCE.
02: Read further address bytes from PARPORT (LL,HH) and send byte at that Add. location back to PC.
03: Read (as above) from PARPORT and write sent byte to specified address into PCE Add.
04: Boot to ROM/RAM, maybe?
05: Send stored registers/MPR to PC from PCE.
06: Send stored registers/MPR from PC to PCE.
07: Send mem range (ADDR, LEN) to PC from PCE.
08: Send mem range (ADDR, LEN) from PC to PCE.
09: Send VRAM version of command 07.
0A: Write VRAM version of command 08.
0B: Fill memory version of 08 (with a single byte value).
0C: Fill VRAM version of 08 (with a word value).
0D: Copy memory (SRCADDR, LEN to ADDR2).
0E: Copy memory (SRCADDR, LEN to VRAMADDR).
0F: Copy VRAMADDR to memory (ADDR, LEN).

10: Copy (move?) VRAM to VRAM
11: Send Physical address (??) to PC from PCE.
12: Read 1 dummy byte from PC to PCE.
13: Send boot MPR regs to PC from PCE.
14: Send boot MPR regs from PC to PCE.
15: Version of command 07 with specified PCE bank.
16: Version of command 08 with specified PCE bank.
17: Send byte data "$24" to PC from PCE then boot to ROM/RAM?
18: Send VCE PAL version of command 07.
19: Write VCE PAL version of command 08.
1A: Send 3 bytes from PC to PCE, written to regs $1C20-$1C22.
1B: Regs $1C20-$1C22 sent to PC from PCE.
1C: Send word data at (ADDR,Bank,LEN) to PC from PCE.
1D: Write word data to (ADDR,Bank,LEN) from PC to PCE.
1E: VRAM version of command 1C.
1F: VRAM version of command 1D.

----

When Hu7 is started up, the code in OutRun does the following:
#$80 -> $1C23
#$00 -> $1C20,$1C21,$1C22
#$01 -> $1C40
#$91 -> $1C03
... wait for $1C02 bits 2,3 to both be high
#$09 -> $1C03
#$0B -> $1C03

... wait for $1C02 bit 3 to be low     ;start of "get byte" routine
read $1C00
#$08 -> $1C03
... wait for $1C02 bit 3 to be high
#$09 -> $1C03                              ;end of "get byte"
-----

here's the "write byte" routine:
byte -> $1C01
#$0A -> $1C03
... wait for $1C02 bit 2 to be low
#$0B -> $1C03
... wait for $1C02 bit 2 to be high

[elmer]

Nice find! 

It sounds like they've left in the stub code for the PC debugger ... that's a bit of a "naughty".

[ccovell]

Here are the HuCards that I found had a Hu7 header in them:

game                    ver.    address

Atomic Robo Kid         1.10    $F400
Deep Blue               1.00    $F800
Drop Rock Hora Hora     1.10    $F400
Drop Off (U)            1.20    $F200
F-1 Pilot               1.00    $F800
Gai Flame               1.20    $F200
Gaia no Monshou         1.00    $F800
Mahjong Goku Special    1.10    $F400
Niko Niko Pun           1.10    $F400
Out Run                 1.10    $F400
P-47                    1.00    $F800
Titan           (? possibly 1.10) ~$F400

Version 1.20 adds about 8 more functions, so I'll look into them.

[MooZ]

I'll try to run etripator on some v1.20 games tonight.

[ccovell]

Do you have a (Win) executable of etripator anywhere for download?

[MooZ]

Yep :

• etripator04.zip
• README
• Examples

For Gai Flame, I'm using this configuration file for the moment:

Code Select Expand

[hu7d]
filename=hu7.asm
type=code
bank=0
org=f243
size=d9
update

• gaiflame.cfg
• labels.cfg
• hu7.asm

[ccovell]

Thanks!  By the way, if you want to test out any of these Hu7 stubs in an emulator, you can change the reset vecs to the start, and change the 3 or so references to bank $FC at the start to $F8 (regular PCE RAM.)

[dangdang]

Interesting.

[ccovell]

Mooz, does your disassembler have a way to add labels to ZP (RAM) locations and absolute addresses used in operands?

[MooZ]

Not yet. It's on the todo list.

[MooZ]

I quickly hacked something.
Labels are now used in opcode arguments.

etripator v0.5 (beta)

[ccovell]

Well, I finished before your latest version came out, but here's my disassembly of the Hu7 routines:

https://www.chrismcovell.com/texts/chris_hu7_dis.asm
https://www.chrismcovell.com/texts/labels.cfg
https://www.chrismcovell.com/texts/gaiflame.cfg

Version 1.20 has 8 more routines that add BRAM, ADPCM, and Supergrafx support.  A few functions, registers, and RAM locations I couldn't figure out how they worked, so let me know if you figure them out.

[MooZ]

cmd11_Send_Phys_Addr_Broken? is super/really weird...
Do you know if it appears in the other games?