stk500 is an Erlang implementation of enough of the STK500 protocol to
talk to an Arduino.

## Example

```
% Open the serial device attached to the Arduino
% The Diecimila uses 19200
{ok,FD} = stk500:open("/dev/ttyUSB0", [{speed, 19200}]),

% Read a hex file generated by the Arduino IDE
%
% hex_file/1 returns a list of binaries as read from the
% file (16 bytes). It's faster to use 128 bytes chunks.

Hex = stk500:hex_file("test/counter.cpp.hex"),
Bytes = stk500:chunk(Hex, 128),

ok = stk500:load(FD, Bytes),

stk500:close(FD).
```

`test/counter.cpp.hex` is a compiled hex file for testing, generated
from the example in examples/counter/counter.pde. To call the example
code from Erlang:

```
1> counter:run(). % loops adding 1 to a counter

2> {ok, FD} = counter:start("/dev/ttyUSB0").
3> counter:read(FD).
{ok, 0}

4> counter:incr(FD).
ok
5> counter:incr(FD, 5).
6> counter:read(FD).
{ok, 6}

7> counter:set(FD, 3).
ok
8> counter:read(FD).
{ok, 3}
```

## Build

```
$ rebar3 compile

# running tests
# arduino is attached to /dev/ttyUSB2
STK500_SERIAL_PORT=/dev/ttyUSB2 rebar3 ct
```

## Note on Protocol Dumping

The simplest way to dump the serial communications is by using strace. For
example, on an Ubuntu system, to see how the Arduino IDE is calling
avrdude:

```
# as root
cd /usr/share/arduino/hardware/tools

mv avrdude avrdude.dist

cat<<EOF>avrdude
#!/bin/sh

set -e

mkdir /tmp/arduino-$$
strace -e read=3 -e write=3 -v -o /tmp/arduino-$$/dump \
-e trace=open,close,read,write,ioctl \
/usr/share/arduino/hardware/tools/avrdude.dist $@
EOF
```

An example protocol dump is doc/protocol_trace.txt.

## Resources

The STK500 protocol documentation can be found here:

```
http://www.atmel.com/Images/doc2525.pdf
```