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mattcallow / CPC_PICOROM

ROM Emulator for the Amstrad CPC. Using a Pi Pico
BSD 3-Clause "New" or "Revised" License
29 stars 4 forks source link

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CPC ROM Emulator using Pi Pico

Features

Quickstart

To load the firmware image:

You have now programed your Pico. It should reboot and appear a USB drive called PICOROM with about 1.5MB capacity. The LED should slowly blink about once per second.

Format the PICOROM

If this is the first time you have have installed the software, or you are upgrading from an earlier verion, you need to format the drive.

Obtain ROM images

You will need some CPC ROM images. You will also need the picorom.rom file, which is in the firmware directory. There are many ROM iamges available here https://www.cpcwiki.eu/index.php/ROM_List
If the PICOROM detects that the ROM file has a AMSDOS header, it will be removed before loading.

As a minimm you will need OS_6128.ROM and BASIC_1.1.ROM. You should also add picorom.rom

At this point, you can test your PICOROM by unplugging the USB cable and plugging it into your CPC. If all is well, the CPC shold boot into Basic 1.1

Create config files

You can create config files from the PC to define what ROMS to load. These files consist of one or more lines like this:

<SLOT>:<ROMFILE>

Where <SLOT> = L for lower ROM or 0-13 for upper ROM bank
and <ROMFILE> = the filename of the ROM to load

For example:

# Default config
L:OS_6128.ROM
0:BASIC_1.1.ROM
1:picorom.rom
2:maxam15.ROM
3:Protext.rom
4:Utopia_v1_25b.ROM
5:Manic_Miner.rom
6:Chuckie.rom

At startup, if the Pico finds a file called DEFAULT.CFG it will load that. Otherwise if will try to load OS_6128.ROM and BASIC_1.1.ROM

Status LED

The LED shows the status of the board:

ROM Commands

If you have loaded the picorom.rom, the you get some new commands on the CPC which let you control the board:

TODO

More details

Completed Board

Signal GPIO CPC Pin Pico Pin
A0-A13 GPIO0-GPIO13 18-5 1-2,4-7,9-12,14-17
D0-D7 GPIO14-GPIO21 26-19 19-22,24-27
~ROMEN GPIO22 42 29
ROMDIS - 43 -
A15 GPIO26 3 31
WRITE_LATCH GPIO27 - 32
CPC RESET GPIO28 40* 34
Pico RESET - - 30

* GPIO28 connected to CPC RESET via a diode

CPC RESET __|\_|___ GPIO28
            |/ |

CPC Reset also has a push button to 0V

WRITE_LATCH signal is created using a Diode-OR gate:

  A13 __|\|___
        |/|  |
             |
  ~WR __|\|__|____  WRITE_LATCH (GPIO27)
        |/|  |
             |
~IORQ __|\|__|
        |/|

All diodes IN4148 or similar. Pulldown provided by GPIO pin.

ROMDIS is connected to 5V

Pico is powered from 5V via a IN4148 diode to VSYS

Pico Reset is a push button to 0V

Notes

At startup, ROMs are loaded into RAM arrays, the the second core emulates all ROM The first core handles the ROM latch at 0xDFxx with the help of a PIO state machine. The same IO port is also used to send commands to the PICO. This is done by writing a series of bytes to the port, startign with a 0xfc (which I don't think is a valid ROM number). Format is as follows:

Data is sent from the PICO to the CPC via a 0xff byte area in the ROM at 0xC100. Format is as follows:

There is a CPC ROM which provides a control over the ROM emulator.

Flash drive

The flash drive is emulated as a USB MSC device. The SPIFTL library is used to provide wear leveling for the flash.

PCB

WARNING There is an error on the schematic and PCB silkscreen. D2 is reversed. So, if you are going to build this, make sure that you insert D2 with the cathode (stripe) at the bottom.

There is a schematic and PCB layout which includes an optional USB interface. Schematic PCB

My PCBs were made by PCBWay. The gerbers I used are also avalilable.

Credits

FatFs - http://elm-chan.org/fsw/ff/ 

/*----------------------------------------------------------------------------/
/  FatFs - Generic FAT Filesystem Module  Rx.xx                               /
/-----------------------------------------------------------------------------/
/
/ Copyright (C) 20xx, ChaN, all right reserved.
/
/ FatFs module is an open source software. Redistribution and use of FatFs in
/ source and binary forms, with or without modification, are permitted provided
/ that the following condition is met:
/
/ 1. Redistributions of source code must retain the above copyright notice,
/    this condition and the following disclaimer.
/
/ This software is provided by the copyright holder and contributors "AS IS"
/ and any warranties related to this software are DISCLAIMED.
/ The copyright owner or contributors be NOT LIABLE for any damages caused
/ by use of this software.
/----------------------------------------------------------------------------*/

USB flash drive code - https://github.com/oyama/pico-usb-flash-drive

Copyright 2024, Hiroyuki OYAMA. All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

- Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this
  list of conditions and the following disclaimer in the documentation and/or
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- Neither the name of the copyright holder nor the names of its contributors may
  be used to endorse or promote products derived from this software without
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “  AS IS”   AND
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

SPIFTL code - https://github.com/earlephilhower/SPIFTL

# SPIFTL - Embedded, Static Wear-Leveling Library
## Copyright 2024, Earle F. Philhower III

                   GNU LESSER GENERAL PUBLIC LICENSE
                       Version 3, 29 June 2007

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