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pwemu

A very work-in-progress Pokéwalker emulator. Definitely not ready for regular use for now.

Dependencies

Only zig for now.

Compiling and running

Compile:

zig build

Run:

zig build run

Or alternatively, run zig-cache/bin/pwemu in a debugger after compiling.

Usage

You need to provide the emulator an EEPROM and flash a ROM image. Right now, this is done by placing two files in the working directory (the directory you run zig build run in):

  • pweep.rom: the EEPROM image (65536 bytes)
  • pwflash.rom: the flash ROM image (49152 bytes)

Once the emulator has started up, the user is greeted with the following prompt:

pc=0x   0 fetched=0x   0 ccr=i------- state=State.reset pending=PendingExn.none
er0=0xaaaaaaaa er1=0xaaaaaaaa er2=0xaaaaaaaa er3=0xaaaaaaaa
er4=0xaaaaaaaa er5=0xaaaaaaaa er6=0xaaaaaaaa er7=0xaaaaaaaa
>

The status of the H8/300H CPU is printed, followed by a > prompt. There, you can enter the number of cycles for which the emulator should run. While running, it'll print some debug info, until it either reaches a breakpoint in the emulator (Sched.ibreak(), recognisable by the B! in the output), or the system has reached the specified number of cycles.

Status

CPU and IO ports implemented, SSU and BMA150 have code to get things working, but need a proper implementation so timings and behavior are actually correct in all cases, and not just for the code the Pokéwalker happens to run. The EEPROM is implemented, and there's a stub for LCD stuff, but it does nothing to display things yet. Some peripherals (ADC, WDT), but the rest isn't (AEC, CMP, I2C, RTC, SCI3, timers), and therefore IR comms, the buzzer, ... aren't, either.

Internal sturcture

Aka, how to get started working on the source code.

If you don't know Zig, it's not that much of a problem. This is my first Zig project, too, so I also don't know much about what I'm doing. You'll probably be fine if you know C and keep this nice overview of the language at hand, as that's what I've been doing.

The entrypoint is in main.zig. It instantiates a Walker (from walker.zig), which represents the entire Pokéwalker (NTR-PHC-01 PCB and components). Most of these components can be found inside the walker/ folder, except for the main H8/38606 MCU, which lives in h838606f.zig.

The 38606 itself only has a few basic functions: init(), reset(), to initialize and reset the system, run() to run the MCU for a specified number of cycles. The readXX() and writeXX() functions access the system bus, and are responsible for address decoding, access timings, etc.

The 38606's MMIO peripherals (timers, serial and IrDA input/output, GPIO, analog inputs, ...) can be found in h83860x/, while the H8/300H CPU of the MCU is in h8300h.zig. The CPU uses code in h8300h/ for instruction decoding and interpreting, and is mostly finished. The interface the MCU uses to talk to the peripherals, are their readXX() and writeXX() functions, which handle MMIO register accesses, as well as their reset() function.

The 38606 can talk to the outside world (i.e. the rest of the PCB), this is done using an Iface struct, containing a few callbacks. The Walker implements these to eg. redirect SPI traffic to the correct component, depending on the GPIO pin state, which acts as chip select.

The final part is the scheduler, in sched.zig. It uses libco (from Higan) under the hood, and has more or less the same features as melonDS' scheduler. The scheduler is used in two different ways: outside the emulated system, you can instruct it to run the emulated system for a specified number of cycles (run()). From inside, you can advance the global time by a given number of cycles (cycle()), as well as schedule 'events' a specified number of cycles into the future. Using libco, the scheduler will switch between the emulated system's thread and the outside world thread as needed.

See this, this, this and this article for byuu's notes on how emulator internals work, especially related to the scheduler. Note that, however, as the Pokéwalker is quite fixed and there's only one main clock, things can be simplified quite a bit, and therefore, this emulator does not implement everything talked about in these articles.

This page has all the documents talking about the innards of the H8/30606F. You most likely need the following files:

  • "H8/300H manual": describes the CPU, its instructions and instruction timings, and so on.
  • "H8/38602 group manual": describes the peripherals, their MMIO registers, and their functions.
  • "H8/38606 update": the document that describes the difference between the '602 and the '606 (namely, different ROM and RAM sizes). Other than that, the '606 as used in the Pokéwalker is identical to the '602.