On Thu, Feb 6, 2014 at 12:24 PM, Kyle Owen <kylevowen at gmail.com> wrote:
I intend to bring out the Raspberry Pi shortly. The
only downside is that
the USB functionality is hindered greatly by the fact that both USB ports
and the Ethernet port all tie into the same bus.
True.
Also, I don't mind running
headless, but with both USB ports taken up by USB-serial converters, I
won't have a spot for a flash drive. Either I'll map a network drive or
just suffer with using the SD card. Then again, if I use a real man's
terminal, I'll save a USB port! :)
I recommend using that real serial port for the connection to the
PDP-8. You could ssh into the R-Pi for control or, for a follow-on
product, it's not hard to stick a textual LCD and a couple of buttons
onto the GPIO header. You can even get them as a pre-assembled
shield.
My other goal is to compile this for an Arduino (or
compatible) and have a
"hands-free" version that can sit nicely in the case of the PDP-8 and not
require any external maintenance.
I love the idea.
I fear though that I won't have enough
RAM in the Arduino to buffer the input stream. I may have to handicap the
handler a bit to fix that.
The lack of RAM in the smaller AVR chips _is_ an impediment. The
larger chips have 4K or even up to 8K of onboard SRAM (up from 1K or
2K), or alternately, some people have had good success with SPI or I2C
RAM. It is likely to be fast enough to buffer incoming packets at
the cost of a few bucks on top of the AVR. Consider, for example, the
ATmega644P or ATmega1284P - as seen in the Sanguino. They have 2
internal UARTs (no serial bitbanging required) and 4K of SRAM. They
come in 40-pin-DIP and 44-pin TQFP, IIRC.
-ethan