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Arduino
RPi modules:
- Serial communication
- Wireless map distribution
- Routing module
Considerations:
- Disable XON/XOFF or bytes 0x11 and 0x13 get eaten by the RPi.
- RPi off, Uno turns on. Uno does not need to wait for RPi.
- RPi already on, Uno just turns on. RPi needs to wait for Uno and then perform
a reset.
- RPi is basically the client (controlling the server)
- Uno is basically the server
[RPi]->Uno serial handshake:
1. Send RESET1 command.
2. Read a byte.
- If it is ACK1, goto 3.
- Else repeat 1.
3. Send RESET2 command.
4. Read a byte.
- If it is ACK1, repeat 4.
- If it is ACK2, finish.
- Else goto 1.
RPi->[Uno] serial handshake (state = UNKNOWN):
1. Read a byte.
- If equal to RESET1, goto 2.
- Else write OUTOFSYNC and finish.
2. Discard buffers and send ACK1.
3. Wait for byte.
- If it is RESET1, goto 2.
- If it is RESET2, write ACK2, set state = READY and finish.
- Else ignore and finish.
Protocol (byte-oriented):
Higher-level header (1-2 bytes):
10.. ....
00 00.. (Handshake, chosen to reduce need to escape signed bytes)
01 RESET1 ([RPi]->Uno) / ACK1 ([Uno]->RPi)
10 RESET2 ([RPi]->Uno) / ACK1 ([Uno]->RPi)
11 OUTOFSYNC, please reset ([Uno]->RPi)
00 0000 PING ([Uno]->RPi) / PONG ([RPi]->Uno)
00 0100 00.. .... DATA_ESCAPE ([Uno]->RPi) Read as 10.. ....
00 1... 101. .... DATA_LEN2 ([Uno]->RPi) max len 256, len=...+1)
.. .... DATA_LEN1 ([Uno]->RPi) max len 56, len=...-7)
Rationale for no PING from RPi to Uno is because the Pi is helpless if the
Arduino died.
Rationale for DATA_ESCAPE is to avoid interpretation as handshake.
Rationale for DATA_LEN2 encoding is to avoid interpreting as handshake, but
still pass the length definition to the control handler.
Note: data length describes the length of decoded bytes following the header.
Example for sending the byte sequence for debug print:
1111 0000 0111 1111 1011 1111
aaaa bbbb cccc dddd eeee ffff
becomes:
1000 0110 1111 0000 0111 1111 1000 0000 0011 1111
(len=3) aaaa bbbb cccc dddd eeee eeee eeee ffff
Data is interpreted as follows:
0... .... .... .... Bits that need to be updated (max 15). The length of the
following data depends on this.
1000 0000 Debug packet, max len is determined by higher-level hdr.
Serial state machine:
init -->-- Device unavailable
/ \
| \
v device connected ^ IO error
| |
\ /
Device available -
RPi architecture
main
|
+-----+------+---------------+
| | |
serial route map sync
I/O finder with others (optional)
route finder:
- updates map based on data updates
- suggests alternative directions
serial I/O
- queues map updates from Uno and fwds to route finder
- takes route suggestions and fwds to Uno
Linear flow:
- I/O (in) has data update
- data update dispatch to route finder
- route finder calculates optimal route to target
- route finder gives next directions
- I/O (out) to Uno
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