RPROM

RPROM

RPROM is a ROM emulator for 16 bit Amiga computers (A500, A600, A2000) based on the RP2350B microcontroller. RPROM was designed in collaboration by Niklas Ekström and Per Bengtsson.

The RPROM board has a 4 MB SPI flash memory. Each ROM image is 512 kB in size, and therefore the 4 MB is divided into eight slots of 512 kB each. The first slot is dedicated to store code and configuration data for the RP2350B. The seven remaining slots are used to store ROM images.

ROM images can be written to flash memory either via USB, or directly from the Amiga using a program called RPROM. This RPROM program is also used to switch which slot is the active slot.

This repository contains the hardware, firmware and software for RPROM. The design is intended to be easily understandable and hackable. For example, the firmware is built from a single, roughly 500 lines long, source code file.

The RPROM command

RPROM is a CLI command that runs on the Amiga. It has the following subcommands:

• RPROM status prints status information about the device
• RPROM switch <slot> switches the active slot and reboots the Amiga
• RPROM write <slot> <image> writes the content of file <image> to slot <slot>
• RPROM read <slot> <image> reads the content of slot <slot> and saves it to file <image>
• RPROM erase <slot> erases slot <slot>

Note that ROM images should not be byte swapped.

Programming using USB

Both the firmware and ROM images can be programmed from a PC using USB. Programming is done using the picotool program, which can be downloaded from https://github.com/raspberrypi/pico-sdk-tools/releases. The RP2350B microcontroller needs to first be in download mode. To put the RP2350B in download mode, hold down the BOOTSEL button on the board, and then click the RUN button. The microcontroller should show up as a USB drive on your PC.

To program the firmware, run picotool load rprom.uf2.

To write a ROM image to a slot, run picotool load <image> -t bin -o <addr>, where <addr> depends on the slot:

• slot 1: 0x10080000
• slot 2: 0x10100000
• slot 3: 0x10180000
• slot 4: 0x10200000
• slot 5: 0x10280000
• slot 6: 0x10300000
• slot 7: 0x10380000

Hardware revisions

There are two revisions of the hardware. The difference between the revisions is quite minor. For rev2, the OE and CE signals have moved from gpio pins 36 and 35 to pins 16 and 17. The benefit of this is that both PIOs with gpiobase=0 and gpiobase=16 can read the OE and CE signals. This in turn results in that using rev2, the time from when the Amiga negates the OE signal to when the RPROM tri-states the data bus is a small number of nanoseconds shorter. In most cases this won't make any difference. In any case, if you are ordering new RPROM PCBs then you likely prefer the latest revision.

Compiling the firmware

In order to compile the firmware you need a recent version (e.g. 2.2.0 or later) of the pico-sdk.

Note that there is a RPROM_REV compile definition in Firmware/CMakeLists.txt that should be equal to the hardware revision that the firmware should be used with. Make sure you set it to the correct value.

License

This design is free for non-comercial use. The designers take no responsibility for if it doesn't work or if it causes damage to your equipment. If you want to build boards to sell then you need to first ask for approval from the designers.

Bill of materials (BOM)

Building

The hardware can be cheaply built by JLCPCB using Economic PCBA. Components should be assembled only on the top side, and select that tooling holes are "Added by Customer".

Please pay attention to the orientation of the components if ordering assembly from JLCPCB. Especially pay attention to the orientation of coil L1. When uploading the component placement file to JLCPCB I had to manually fix the orientation of L1 regardless of what the component placement file specified.