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Old 24 July 2018, 10:43   #1
betajaen
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Raspberry Pi Mini to 1200 Clockport Advice

Hello All,

This has probably been talked to death. But it's worth a short. Let's say I want to connect a raspberry pi mini to the 1200 clockport, via a cable from the GPIO pins of the RPI, which is powered via USB externally.

I believe you can control the pins by hand, so no need for i2c, spi, r232 or other fancy protocols.

Let's assume, I'm a complete idiot to electronics, no matter how much I try and learn it doesn't stick. I have all the bits and pieces; cables, dev-boards, etc. However, I'm pretty good at programming (if I may do say so myself), so software side of things not a problem.

I assume I couldn't just wire the pins 1:1 to them, would there have to be some capacitors, resistors, motors, flux-capacitors, etc. and what about voltage?

Hope someone can help.

Thank you,

Robin/Betajaen
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Old 24 July 2018, 21:05   #2
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The voltage needs to be adapted, the Amiga does 5V and the RPi GPIO is 3.3V.

You will also need to write drivers for both ends.
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Old 24 July 2018, 21:17   #3
nogginthenog
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Betajaen: 3.3v <> 5v logic level convertors are cheap and super easy to use. No flux capacitors required
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Old 24 July 2018, 22:11   #4
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Thanks guys.

Don't worry, I'll be writing those drivers.

Do you mean something like this nogginthenog?

https://www.sparkfun.com/products/12009

Because if it's as easy as that, I can get plenty.
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Old 25 July 2018, 00:05   #5
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Yes, exactly that. 4 pins might be a bit limited.
I used these in a recent project (RPI to C64 floppy emulator)

https://www.aliexpress.com/item/I2C-...816690842.html

Or not China:

https://www.ebay.co.uk/itm/1-5PCS-8-...o/351447294920

You might want to look at Raspberry PI to Arduino as this is quite common and (most) Arduinos run at 5v. Good luck!
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Old 25 July 2018, 09:27   #6
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Brilliant. Thankyou. I ordered 5

Presumingly I can do the same thing with an Arduino (Clockport to Arduino), but since it runs at 5 volts, I wouldn't need the 3.3v <> 5 voltage converters. Just direct wires to the digital pins?

Then at least, I can use the Arduino to listen into the clockport, and output it via serial to my PC? For debugging purposes, and understanding the timing and how it all works.

Thankyou - again, this was easier than I thought.
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Old 25 July 2018, 20:29   #7
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I don't see why not. I would recommend connecting the GND on the Arduino to the GND on the clockport so the Amiga & Arduino have a common ground.

Thinking about this, it might be a nice way to connect a I2C or SPI device to the Amiga. I wouldn't expect high speed!
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Old 25 July 2018, 22:07   #8
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Good idea! Could I power the Arduino off the clockport as well?

The plan was to see if I could use a Raspberry Pi, as a "$5 HDMI graphics card". I have a Subway USB connected to my Clockport, and it's not very fast. First step is to use an Arduino to look at the communication methods, timing, etc. But we'll see.

But if it doesn't work, then I may tackle the expansion slot - but that is a HUGE can of worms. Really, I just need access to the main CPU address and data buses.
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Old 26 July 2018, 00:17   #9
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Arduinos in general are pretty low power so it should be OK. I doubt you're going to make a gfx card but maybe a small oled display is doable.

None of my Amigas has a clock port so I'm just guessing!

BTW Arduino is more of a programming API. I've got many 'Arduinos' that can be programmed with the Arduino GUI: Nano, Micro, Mini, ESP3266, ATmega32, ATtiny86 & ATtiny13.
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Old 26 July 2018, 10:24   #10
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I have a few arduinos as well, including the ESP3266 which would be a nice Wifi board come to think about it. I quite like the ATtiny86 personally.

However; The Raspberry Pi has a bit more oomph than the AVR processors, so it's more than capable of outputting a HDMI video. Trick is for the Amiga to keep up, and can it? Only one way to find out.
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Old 26 July 2018, 11:35   #11
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You'll find yourself limited by the clock port bandwidth. Unless... maybe you can just forward the graphics.library calls as-is to the pi and do all the drawing there.
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Old 26 July 2018, 13:42   #12
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That was I was thinking, just a light wrapper/driver. My biggest concern was transferring any bitmap data over, how long that would take to do.
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Old 26 July 2018, 14:15   #13
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Many years ago there was a similar concept, the Siamese System, which redirected graphics.library calls over a network connection to a PC. Apparently it worked surprisingly well, despite the bandwidth limitations. Moving bitmaps were quite laggy however, as you would rightly expect.

Bear in mind that there is already an SPI adaptor available for the clock port That would save a lot of work if you're looking to attach an SPI-driven display, network adaptor or whatever. All you'd need are the device drivers for whatever you're connecting.

Edit: I see it's not available yet - it should be very close though...
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Old 26 July 2018, 18:06   #14
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Interesting. I think I remember something about that in Amiga Format (Siamese Systems?)

I think my interest in the project is, that someone can buy a cable of ebay, a Raspberry Pi, flash an SD card, and fit it into their Amiga. No complex or expensive hardware.

Even if the display doesn't work out exactly as planned, it could be useful. There is also the USB stack that could be used, the SD card for extra storage, or even the WiFi. Even the ARM processor could be used a slow-but-fast co-processor.
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Old 26 July 2018, 21:01   #15
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One thing to remember is that a PI runs Linux and a Arduino microcontroller is just bare metal. So if you need fast polling or fast interrupts a PI might be an issue.
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Old 26 July 2018, 22:18   #16
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You can write bare metal on the raspberry pi. No need for Linux, you just basically write a simple 'bootloader' which is copy-paste assembly, then you can write the rest in C. Direct access to the hardware. Just include libs as needed.

I am going to mess around with the Arduino first though...it's easier to debug with, and I have a output console, I can read from.
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Old 26 July 2018, 23:41   #17
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Of course :-) But it's not easy. Ask Bloodline: http://eab.abime.net/showthread.php?p=1212968

My C64 is connected to a PI3 running a 1541 emulator. Bare metal as it needs accurate timing. Mine is a mess of wires but I'm making a PCB.

https://cbm-pi1541.firebaseapp.com/
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Old 27 July 2018, 10:17   #18
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Thanks for the links, I had a quick peek/read, but I shall be investigating those in full later.

Thanks again for all of this.
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Old 27 July 2018, 11:39   #19
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@betajaen - what is the idea of this, what do you want the thing to DO???
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Old 27 July 2018, 17:09   #20
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Essentially, I want to hook up a Raspberry Pi to an Amiga 1200 via the clockport. The intention with written drivers (on both sides), is for the Raspberry Pi to act as a realtime graphics card for the Amiga. Taking advantage of the higher screen modes, HDMI output, and extra speed.
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