Fast serial port/SD card adapter for the 1MHz Bus

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myelin
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Fast serial port/SD card adapter for the 1MHz Bus

Postby myelin » Fri Nov 10, 2017 11:03 pm

Another new project... this is something I started on ages ago and finally got some PCBs made. It's a CPLD/MCU board that provides a (very) fast USB serial connection for anything with a 1MHz Bus (BBC B/B+/Master, or Electron+AP5). On my Electron, using the prototype of this, I managed to get 39 kB/s (the equivalent of 390 kbaud in a real serial port) in MODE 6

The PCBs just arrived in the mail, so I should have them tested sometime in the next couple of weeks.

serial_front.jpg

It's open source (Apache 2.0 license) like all my other Acorn hardware, and the latest designs live on GitHub here: https://github.com/google/myelin-acorn- ... sd_adapter
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.

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tricky
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Re: Fast serial port/SD card adapter for the 1MHz Bus

Postby tricky » Sat Nov 11, 2017 7:23 am

Very nice, I was thinking about something similar in the week. I was thinking MMC but with options for some combination of user port/ADC/speech/D2A. The main difference is that I would g never have got mine made.
Well done =D>

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myelin
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Re: Fast serial port/SD card adapter for the 1MHz Bus

Postby myelin » Fri Nov 17, 2017 5:53 pm

... and it works!

I have it running JGH's HostFS, with the only changes being the port addresses (I have TxData and RxData on &FCA0, and TxStatus and RxStatus on &FCA1), and it works beautifully. With my WaitLoadIO fast path, it gets 29 kB/s on pretty much all transfers. Not sure why it's slower than the Electron version, but it's still very quick.

2017-11-installed_in_bbc.jpeg

(Pictured with USB cable disconnected)

I haven't tried out the SD port yet, but I should be able to get MMFS working without too much trouble, using the Electron Plus 1 interface (and maybe the fast shift register interface, although the CPLD is getting pretty full).
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.

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myelin
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Re: Fast serial port/SD card adapter for the 1MHz Bus

Postby myelin » Sat Dec 02, 2017 1:12 am

I just posted one of these off to Dominic Beesley, and it appears that a single PCB just counts as a "letter" to the USPS, which means I can post them out pretty cheaply to anyone who wants one. I don't have time to assemble them, but if anyone wants a bare PCB, PM me an address and I'll post you one!
SW/EE from New Zealand, now in San Francisco: http://myelin.nz/
Having fun making hardware projects for the Electron!
So far: 32k flash cart, USB cart interface, 3-cart expansion, Elk PiTubeDirect. Later: Dual ported ram cart.

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danielj
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Re: Fast serial port/SD card adapter for the 1MHz Bus

Postby danielj » Sat Dec 02, 2017 7:24 am

=D> very impressed! I'd love one, and if anyone wants some putting together, I'm happy to oblige (you can ping them directly to me and I'll construct and pass on). Will drop PM shortly :)


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