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Marvin 1.5

Firmware for the BeanZee Z80 family: a simple monitor program, with submodule extensions.

Hardware Targets

  • beanzee is a small Z80 single board computer which is accessible only via a USB interface and a host computer with a console emulator
  • beanboard adds a small LCD display and self-contained keyboard to BeanZee, providing direct interaction with the computer in addition to USB; there's also a GPIO to facilitate experimentation
  • beandeck is a work-in-progress and incorporates BeanBoardSPI through which a 7" 800x480 colour TFT and flash storage is added to the beanboard, making a self-contained Z80 computer (BeanBoard LCD display is removed to install this board)
  • beandeck_reva incorporates BeanBoardSPI Rev A - the original revision of the board which should NOT be used, and is provided for interest only - this first revision requires software delays while hardware serialisation occurs, whereas subsequent revisions poll a status register

Submodules

The build optionally embeds RT Russell's BBCZ80 BASIC interpreter in a git submodule.

Marvin provides the glue between BBCZ80 and the hardware. Marvin console I/O and BFDS filesystem are connected:SAVE and LOAD read and write BDFS files and * commands are dispatched to the Marvin monitor (e.g. file directory)

A second ra8875-z80 driver git submodule is added for the beandeck target. This provides low-level interaction with an Adafruit RA8875 TFT controller, configured for an 800x480 TFT display, and a simple console layer for the display supporting a software cursor, wrapping and scrolling.

Building

Requires z88dk (z88dk-z80asm).

Clone repo with submodules:

git clone --recurse-submodules https://github.com/PainfulDiodes/marvin.git

The build script assembles all submodule sources directly — you do not need to build the submodules separately:

./build.sh

Output binaries are placed in targets/<target>/output/.

For each target there is full "marvin" output which includes the BASIC interpreter, and in addition a "marvin_minimal" output which contains only the monitor program.

Memory Map

  • 0x0000 - 0x7FFF : 32k ROM (firmware)
  • 0x8000 - 0xEFFF : User program area
  • 0xF000 - 0xFFFF : System RAM (monitor use + stack)

Stack starts at 0xFFFF (working down).

Trampoline Functions (ABI)

Fixed ROM entry point addresses for target-independent access from Z80 assembly and C programs: abi/marvin.inc

Each entry is a JP trampoline at a fixed address. Entries not supported on a given target are stubs that return immediately without hanging.

Usage (z88dk assembly):

INCLUDE "marvin.inc"

    LD HL, message
    CALL MARVIN_PUTS    ; write string to active console

message: DEFM "Hello!\n", 0

Monitor Commands

See: monitor

BBC BASIC

RT Russell's Z80 BASIC interpreter can be launched from the monitor prompt:

  • b - cold start (clears variables and program)
  • B - warm start (retains existing program)

From BASIC you can access BDFS with SAVE "name.ext" and LOAD "name.ext". If the filename extension is missed, ".BBC" is assumed. You may also use * to run any monitor command.

Return to the monitor with:

  • QUIT

Links