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 Question: removable storage for a hombrew CPU SBC 
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Joined: Wed May 15, 2019 1:17 am
Posts: 21
Hi all. Once I finish up on my 8-bit TTL CPU (, I was thinking of looking at some of the existing minimal 68020 SBCs: the aim would be to port the xv6 system to the SBC. Link:

To do this, I'd want to add some form of removable storage, so I could build a filesystem on the storage with an existing system. Does anybody have any recommendations on suitable removable storage that could be, or has been, added to a homebrew SBC?

So far I was thinking of an SD card in SPI mode, with some shift registers to interface between the card and the CPU.

Any other ideas and suggestions most appreciated!

Wed May 15, 2019 1:32 am

Joined: Tue Dec 11, 2012 8:03 am
Posts: 285
Location: California
We had a similar discussion on the "Brad's Projects" forum:
super-simple file system for flash memory

_________________ lots of 6502 resources

Wed May 15, 2019 1:47 am WWW

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1690
SD card would certainly be my first thought: you don't necessarily need any shift registers, because you're providing both clock and data, so you can proceed as slowly and irregularly as you like.

There is then the question of what you do with the blocks that you read or write: whether to do the normal but slightly complex thing of recognising partition tables and a FAT filesystem, or roll your own mini filesystem, or treat the SD card as sequential block storage, or something in between.

One of the standard SD Card approaches for Acorn's BBC Micro is to have a rather minimal FAT implementation which just reads one file in the root directory: that file contains a number of disk images and then the disk filing system accesses those in the usual way by reading and writing sectors. In this way there's a minimal but useful compatibility with updating or saving the one big file on a PC. However, this approach builds on top of an existing disk file system, which you don't - yet - have.

Wed May 15, 2019 7:47 am
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