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Re: Apple II Pi
David Schmenk <dschmenk@gmail.com> wrote:
> On Thursday, 23 May 2013 17:58:45 UTC-7, Michael J. Mahon wrote:
>> David Schmenk <dschmenk@gmail.com> wrote:
>>
>>> This weeks project:
>>
>>>
>>
>>> http://youtu.be/Kx_ggKHWaxA
>>
>>
>>
>> Dave,
>>
>>
>>
>> You can probably use the RPi GPIO pins to eliminate the need for a serial
>>
>> link... It shouldn't take more than an octal transceiver connected between
>>
>> the RPi and the Apple bus--controlled by the Apple bus.
>>
>>
>>
>> -michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
>
>
> The RPi GPIO pins really aren't as powerful as you might think. The
> choice by the Raspberry Pi foundation as to which pins to bring out to
> the header, was, um, a little odd.
That's too bad--I find it hard to imagine that there wouldn't be at least
an 8-bit port there, plus a couple of lines for handshaking/interrupts.
I wonder what part of GPIO they misunderstood? Or maybe it's a limitation
of the Broadcom part...
> Once I gave in to using the serial interface as the communication channel
> and using the 6502 to do the dirty work, it actually made things much
> easier. For one, it's pretty hard to service interrupts for the Apple
> Mouse remotely. As I'm running the serial link at 115K and the
> communication traffic is pretty light, performance isn't much of an
> issue. I would like to add the ability to read and write Apple II memory
> from the RPi, as well as call code on the Apple II - kind of like a retro Arduino.
The first three commands/transactions I implemented for NadaNet, back in
the beginning, were peek, poke, and call. ;-). I figured if necessary I
could build anything else out of those!
> My thoughts on the IIe expansion card are to use a 6551 (same as the
> SuperSerial Card) but derive it's baud rate clock from the RPi's GPIO
> general purpose clock pin (thus saving a crystal). Also connecting one
> of the GPIO pins to the 6502 RESET line would allow the RPI to reboot the
> Apple II if it hung. Then we could play with the Apple II's I/O bus from Linux.
Just out of curiosity, if GPIO can't control a transceiver, how do you
manage to interact with the Apple bus?
-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon