Alternative to typing: SPI through game port

Instead of typing, if you have a way to spit SPI slow enough
(for example, with doc/hw/avr/spispit), you can record that data
through the game port.

It's hacking because the game port only has inputs, but if you
perform checksums on both sides, you can end up with good data.

The game port is a DB9 that has the following pinout:

5 4 3 2 1
 9 8 7 6

1 - SW1
2 - +5V
3 - GND
4 - PDL2
5 - PDL0
6 - SW2
7 - SW0
8 - PDL1
9 - PDL3

In my own setup, I used an Arduino because I could power it
directly from the port, which simplifies interfacing (I can wire
directly).

We use only SW0, plugged to SCK and SW1, plugged to MOSI.

SW* are mapped to memory thus:

SW0 - C061
SW1 - C062
SW2 - C063

Only bit 7 is relevant (1=high), the rest is garbage.

The idea is that we point to an address in memory, and then
run an infinite loop that shifts data in A 8 times, then writes
to memory.

The code for doing this is:

\ Receive SPI data through game port
\ Plug SCK in SW0 and MOSI in SW1, then run the program
\ ZP+7 must contain the destination's page.
0 # LDY, 6 <> STY, BEGIN,
  1 # LDA, BEGIN, \ 8 times
    BEGIN, $c061 () LDX, ( SW0 ) BR BPL, \ SW0 high!
    CLC, $c062 () LDX, ( SW1 ) FJR BPL, SEC, THEN, ROLA,
    BEGIN, $c061 () LDX, ( SW0 ) BR BMI, \ SW0 low!
    BR BCC,
  6 []Y+ STA, INY, IFZ, 7 <> INC, THEN, BR BCS,

You might not have Collapse OS on the IIe yet, so you'll have
to type this with the integrated mini assembler. It's position
independant, so you can put it anywhere.

The idea is that before you launch the code, you set the dest-
ination page in ZP+1 (ZP+0 stays at 0 at all times). Then, you
call the code and then spit your SPI. Once it's spit, press
CTRL+RESET to come back to AppleSoft prompt. If everything went
well, you have your data in memory, do stuff with it.

Note that reading the port with the 6502 at 1MHz represents an
important constraint: your SPI spitter has to be pretty slow! At
about 30 cycles for the main loop, you can expect to miss data
if you spit faster than 30KHz.

Be careful, SW0 is hard-wired to "Open-Apple" key and SW1, to
"Solid-Apple". This can have weird effects on warm boot-up, so
you might want to disconnect your SPI spitter before you reset.

If you use the Arduino SPI spitter from doc/hw/avr/spispit, you
need to ignore the first 3 SCK toggles. You can do that by pre-
pending the above code with:

$20 # LDA, BEGIN, \ 3 times
  BEGIN, $c061 () LDX, ( SW0 ) BR BPL, \ SW0 high!
  BEGIN, $c061 () LDX, ( SW0 ) BR BMI, \ SW0 low!
  ROLA, BR BCC,

Reboot afterwards

After you got your data in, that you've checked that it's
correct and that you've saved it to disk, I recommend that you
reboot before launching your binary.

In my tests, the computer exhibited buggy behavior right after
a run of the procedure above, which only a clean reboot could
fix.