BBC Micro on MISTer

During Covid-19 lockdown one of the things I wanted to do was to revisit some of the old computers I used. I don’t really have the space or inclination so collect the original hardware, so I decided to try out what emulation options exist now.

I have been interested in trying some ASIC based projects, so a natural choice seemed to me to use the MISTer platform. This is a retro computer, console and arcade emulation system based on the DE-10 Nano FPGA development board. This MISTer project was developed from the earlier MIST project which used an older development board.

To get started with MISTer you just need the DE-10 Nano board, but I also chose to get the MISTer add-on board, mostly for the secondary SD Card (more on that later). Most of the emulation cores, but not the BBC Micro, need a RAM add-on board too.

Once you have the DE10 you can just flash the MISTer core on to an SD Card and boot it. You will also need a USB keyboard connected to the “USB to go” socket.

Some useful keys:
CTRL-F11   Break (BBC Micro)
F12        Load MISTer menu

One limitation of the current core is that it doesn’t support split-mode games like Elite and Revs.

Using BEEB.MMD

The BBC Micro core uses files in “MMB” format. This was a format originally developed for a BBC Micro add-on that connects SD cards to the user port and makes it look like a virtual set of disk-drive. The MMB file is a bundle of hundreds of BBC floppy disk images. Using commands on the BBC Micro you can choose to mount the images from the file in to virtual drives.

The BBC core offers two ways to mount the MMB file. If you have a secondary SD card then format as FAT32 or FAT16. Copy the MMB file as “BEEB.MMB” on to the card. The core will automatically pick up that card. In this mode the file can be both read and written.

The alternative is to rename the file as “.VHD” and copy it to the “games/BBC Micro” directory on the main SD Card. If it is called “boot.vhd” then it will be automatically loaded. If not then you can manually load from the MISTer menu. In this mode the file is read only. To unmount a previously mounted VHD (e.g. to go back to the secondary card) press backspace when picking the VHD.

There are various utilities to manipulate MMB files on PCs. I used “MMBReader” which is available on the stardot forum. On the emulated BBC Micro the MMB file is accessible using MMFS. Note that if no MMB file is available then MMFS will stall the boot of the BBC Micro by displaying the message “CARD?”.

Some useful MMFS Commands:
 *DCAT [start #] [end #]   - List disks in the MMB file
 *DIN [Drive #] <Disk #>   - Mount disk in the specified drive (default 0)

Most of the MMB files you will find on the web are pre-loaded with many original games. By default they boot in to a menu to pick the games. You can disable the autoboot on the first disk by using the command *OPT 4,0. If you subsequently want to run the boot use *EXEC !BOOT.