Raspberry PI

[JimS]

That or using the PI like a bridge board or how about as a video card? All these things have crossed my mind. I'm a software dev and love to sit down with a good hardware dev for a day or two to know more about things like PICs and working with and wiring up a GPIO.

I've been thinking of using a microcontroller board as some kind of super I/O board for a classic Amiga. There are a lot of chips out there that do cool stuff like mp3 decoding, radio reciever, networking and usb hosting. Seems like a microcontroller could host these - via SPI. and communicate with the Amiga via a parallel interface.
One thing to consider, I'm almost sure the PI uses 3.3v logic. You'd need some level shifting to connect to the Amiga.

[JimS]

Before I ordered the PI, I was all about trying to figure out a way to arduino-up my Amiga. I'd still be interested. It's so frustrating for me because I understand just enough to not be able to know the right direction about how to best use the hardware.

I was thinking about the arduino as well as some other boards maybe ARM or Propellor based.

Also, Amigas are not a dime a dozen so the thought of damaging one in testing also frightens me. So, I understand that most modern electronics use 3.3 volts and older stuff like the Amiga uses 5 volts. How do you do "level shifting"?

There are lots of ways, from resistors & diodes to custom chips made just for level shifting. Peruse the adafruit or sparkfun web sites for some ideas...

Also I asked earlier about the fastest interface area. I know the mediator, for example, has a pass-thru for the cpu 150 pin slot adapter for the A1200. Perhaps something like that would provide the best solution, but how do you make subsequent attachments work?

I don't know about speed. What I had in mind was making a card for the Zorro bus (but too lazy to do autoconfig) that implemented a 16 bit parallel port. Just a matter of decoding the Amiga's address bus to pick some spare address. Add a couple of handshaking lines and you need less than 20 lines. Because I was thinking of multiple devices on the other end of the microcontroller, the Amiga would send over a control word first with a device address. The micro would then route the data as needed. At least that's kinda what I was thinking.

I've also read that you may need a PIC or something (again, what is a PIC) to create/call/provide (?!) interrupts at the 14MHz cycle in order to make the rest of the hardware happy if you wish to provide some sort of accelerator.

A PIC is just another type of microcontroller chip

Do you need to connect to all 150 pins? What is the minimum needed if your microcontroller/microcomputer has only in the range of 25-35 GPIO pins?

Like I said, for what I had in mind, I'd only need about 20 pins. But if you want an accellerator, GPIO is irrelevant. What you need are the CPU's address and memory busses. Those aren't necessarily available outside the chip.  

I would love to get into an IRC chatroom with anybody capable and patient enough to explain this stuff to me; or better yet, in person in you're in San Jose, CA.

You can try the Sunday nite Asha chat on irc.superhosts.net  #team*amiga  
We meet Sundays at 9pm EST. Sometimes some hardware knowlegeable folk show up.

[JimS]

What is wrong with the physical parallel port on the backside of the Amiga's? Are they too slow? Were you planning on something else so that it could be handled from the inside of the machine?

Nothing wrong with the built in port... except that it's only 8 bits wide.... and I'd prefer to leave it for the printer. BTW. "planning" is too strong a word. ;-) It's just some ideas I've been mulling around.

[JimS]

Interesting, so would you say that each GPIO pin is roughly a bit given it's states are likely high or low. Therefore if you had 8 pins you could spit out roughly a byte at a time? Is that how this works. Give some signal to read, the software reads the state of pins 0-7 and assigns their values to bits 0-7 respectively and then either waits for the next read now signal or otherwise signals the device that it's ready for the next byte's worth of bit/GPIO pin values?

Is this roughly how data transfer between them would take place?

That's exactly how it would work.

Or could you do something like set the voltage on the GPIO pin to be a value between 0.0v and 0.256v and read the voltage as a byte value? Not sure how precise voltage can be set and read.

No, I don't think that would work... too inaccurate.

What are the maximum throughput values if it's used like this? Sorry if this is way OT, but I'm just pondering in "out loud" in these POSTs now.

Maximum thruput would most likely be limited by the clock speed of the CPUs on either side of the link. Probably the Amiga side would be the limiting factor.