Nest Hacking
Info
- /dev/event1 is the knob; /dev/event2 is the button
Nest software
/nestlabs/sbin/nlclient -config /nestlabs/etc/client.config -config /nestlabs/etc/Display/Display-2/client.config
Backplate firmware
Found in /nestlabs/share/bp/data/firmware/nlbpfirmware.plist
Nest backplate interface
- Connected on /dev/ttyO2
- All communications with backplane begin with (d5)d5aa96 (d5 is doubled only for data FROM backplane)
- 16-bit command
- 16-bit data length
- 16-bit checksum
Monitor:
strace -ff -p $(pidof nlclient) -x -s9999 -e read,write 2>&1 | grep '(54'
Checksum
<Bytes-from-end>.<bit-value> <xor-with>
00.01 2110 (1021) 00.02 4220 (2042: 1021<<1) 00.04 8440 (4084: 2048<<1) 00.08 0881 (8108: 4084<<1) 00.10 3112 (1231: 8108<<1^1021) 00.20 6224 (2462: 1231<<1) 00.40 c448 (48c4: 2462<<1) 00.80 8891 (9188: 48c4<<1) 01.01 3133 (3313: 9188<<1^1021) 01.02 6266 01.04 c4cc 01.08 a989 01.10 7303 01.20 e606 01.40 cc0d 01.80 981b 02.01 3037 02.02 606e ... 03.01 b476 03.02 68ed 03.04 f1ca 03.08 c385 03.10 a71b 03.20 4e37 03.40 9c6e 03.80 38dd ... 07.20 687b
If you compute the contribution of the individual bit changes in the data you end up with the xor table above; byte offset from the end of the data, bit pattern, xor value. Correcting for little endianess in the output you end up with the hex values in parenthesis. The least significant bit is 0x1021 and each subsequent bit is a shift left, if the XOR value has the 0x8000 bit set then it is XORed with 0x1021. This is the CRC-CCITT polynomial.
8 7 6 5 4 3 2 1 0
d5 aa 96 82 00 02 00 00 00: 08b2
|| |
|| 68ed
|408b
20d4
08b2: 68ed ^ 408b ^ 20d4
Starting at the least significant bit and filling in the XOR values for each bit gives the above diagram; the diagram stops at the 20d4 XOR value because at that point it matches the final CRC. This tells us that the CRC covers the 6 bytes prior.
#!/usr/bin/env perl
use Digest::CRC qw(crc);
my $data = pack("H*", "820002000000");
printf("%04x\n", crc($data,16,0,0,0,0x1021,0,0));
We can also compute the same CRC in Perl; note the result will be byte swapped since the data encodes the number as little endian.
Command ids
Display to backplane
0082 - FET control 0083 - 008f - FET presence 0090 - 0098 - 0099 - 009b - 009c - 009d - 009e - 009f - 00a1 - 00a2 - 00a3 - 00a4 - 00b1 - 00b3 - 00b5 - 00b9 - 00ba - 00c2 - 00ff -
Backplane to display
0000 - 0001 - 0002 - 0004 - FET presence 0005 - 0007 - 0009 - FET presence 000a - 000b - 000c - 000e - 0010 - 0014 - 0018 - 0019 - 001b - 001c - 001d - 001e - 001f - 0022 - 0023 - 0025 - 0027 - 0029 - 002a - 002b - 002f - 0038 - 003f - 0070 - 020d -
FET control
Turn on W1: d5aa96 8200 0200 00 01 29a2 Turn off W1: d5aa96 8200 0200 00 00 08b2 Turn on Y1: d5aa96 8200 0200 01 01 1891 Turn off Y1: d5aa96 8200 0200 01 00 3981 Turn on G : d5aa96 8200 0200 02 01 4bc4 Turn off G : d5aa96 8200 0200 02 00 6ad4 Turn on OB: d5aa96 8200 0200 03 01 7af7 Turn off OB: d5aa96 8200 0200 03 00 5be7 Turn on W2: d5aa96 8200 0200 04 01 ed6e Turn off W2: d5aa96 8200 0200 04 00 cc7e Turn on Y2: d5aa96 8200 0200 07 01 be3b Turn off Y2: d5aa96 8200 0200 07 00 9f2b Turn on * : d5aa96 8200 0200 0b 01 d37e Turn off * : d5aa96 8200 0200 0b 00 f26e
For the sake of documentation, we will refer to the unique id numbers for each wire as "wire id numbers". So wire id 0 is W1, wire id 1 is Y1, wire id B is *, etc.
FET presence
The backplate will, at least upon connection, send information about which FETs have a wire present. This data is received with command ids 0004, 0009, and 008f, in that order. Each sensor is represented by one byte which is either 00 (not present) or 01 (present).
The content of 0004 and 008f appears to be identically formatted, and in order of the "wire id numbers" used for control: W1, Y1, G, OB, W2, ?0, ?0, Y2, ?1, ?1, ?0, *, ?0
The content of 0009 is arranged differently and has 2 more values: W1, Y1, ?1, ?1, ?0, G, OB, W2, ?0, Y2, ?0, *, ?0, ?0, ?0
Run BeagleBone/Debian programs
ln -s . /lib/arm-linux-gnueabihf ln -s ld-2.11.1.so /lib/ld-linux-armhf.so.3
