[Coco] Becker port

[RETRO Innovations]

On 4/21/2019 1:43 PM, Michael Furman wrote:
> Over the past few years I have been pitching the idea of building a hardware Becker port for real cocos to the hardware wizards in this group.  I had even proposed that it would be possible to interface a Becker port to SPI and that could open up some some possibilities.  For example the ESP8266 does have a SPI access mode which as far as I know has not been has explored.  It also could be interesting to interface to a CH375 usb drive adapter. Wiznet Ethernet adapter, SD card, a lot of possibilities here.
>
> I have a breadboard prototype of a hardware Becker port interface connected to an Arduino Mega but I haven’t had really had much time to work on it lately.
>
> Sent from my iPad

I think the hesitation is the nature of the port.  Gary designed the 
port as a shortcut to expose some peripherals to the CoCo3FPGA so he 
could continue development in other areas and folks could utilize what 
he had developed so far.  I don't know that Gary intended on it being a 
standard of any kind.

It has a few issues:

  * It's nonstandard.  One must use a patched OS to leverage the port.
  * It sits right int he same space as the FDC and related items
    (CoCoSDC).  Thus, it requires one to use a MPI to enable it to share
    space with other peripherals.  Not horrid, but makes it a bit harder
    than if it was i the upper $ff5x range or maybe $ff7x.
  * It doesn't offer much in the way of configuration.  Thus, one must
    depend on the drivewire protocol (or the protocol that resides on
    the port) to support any configuration options the endpoint device
    might need.
  * It does not offer interrupts, as I recall.  Some apps needs an
    interrupt-driven data transfer.

Please understand I'm not faulting the port for its initial purpose.  As 
a designer, I am sure Gary was focusing on other aspects of the CoCo 
emulation and didn't want to spend a lot of time implementing a bit-bang 
receiver on the other end of the software serial port, so this was a 
great way to quickly bolt up a real or virtual serial port so he could 
spend time elsewhere.

Jim