Instrument control package

Instrument-Control is a package for interfacing the outside world of hardware via Serial, i2c or Parallel interfaces. It is currently under development by Andrius Sutas, you can browse the SVN repository here and download the package here.

Compatibility

Below is a table showing package compatibility with various platforms:

	Linux	Windows (Cygwin)	FreeBSD	Mac OS X
Serial	v0.1.0	WIP	WIP	WIP
Parallel	v0.1.0	-	WIP	-
i2c	v0.1.0	-	WIP	-

Where: (VER) - Included since VER version; (WIP) - Work In Progress and will probably be included in next release; (-) - Not supported / Untested.

Examples

Serial

Configuring interface

You might want to configure interface in a loopback mode for testing.

• If you have a Serial adapter, then simply connect pins 3 (Tx) and 2 (Rx) together (assuming your adapter is RS-232 DE9, otherwise check before doing anything). One can also insert an LED in series to view the actual bitstream.
• If you do not have a Serial adapter then create a virtual port using:

$ socat PTY,link=/dev/ttyS15 PTY,link=/dev/ttyS16

which will open two interconnected interfaces, where one (e.g. /dev/ttyS15) can be opened in Octave and second (e.g. /dev/ttyS16) using something like GNU screen:

$ screen /dev/ttyS16 <baudrate>

do not forget to change interface permissions if you want to use them with Octave/screen without root privileges.

Example: basic use

Here is a simple example to get started with the serial package. It tests the RxD and TxD lines. Make sure you have defined a loopback or connected the pins of your adapter.

Code: Serial port example

# Open default serial port ttyUSB0 in default configuration of 115200, 8-N-1 s0 = serial() # Opens serial port ttyUSB1 with baudrate of 115200 (config defaults to 8-N-1) s1 = serial("/dev/ttyUSB1", 115200) # Flush input and output buffers srl_flush(s1); # Blocking write call, currently only accepts strings srl_write(s1, "Hello world!") # Blocking read call, returns uint8 array of exactly 12 bytes read data = srl_read(s1, 12) # Convert uint8 array to string, char(data)

Chaging some configurations is simple done by calling helper functions

Code: Serial port example: helper functions

srl_baudrate(s1, 9600) # Change baudrate srl_bytesize(s1, 5) # Change byte size (config becomes 5-N-1) srl_parity(s1, "E") # Changes parity checking (config becomes 5-E-1), # possible values [E]ven, [O]dd, [N]one. srl_stopbits(s1, 2) # Changes stop bits (config becomes 5-E-2), possible # values 1, 2.

Some properties can be set at opening time

Code: Serial port example: constructor call

s2 = serial("/dev/ttyS0", 9600, 10) # Opens serial port ttyS0 in # 9600 baudrate with 1s read timeout

Do not forget to close the ports when you are done!

srl_close(s0) # Closes and releases file descriptor srl_close(s1) # Closes and releases file descriptor srl_close(s2) # Closes and releases file descriptor

Parallel

Configuring interface

You will need to load following modules:

# modprobe parport
# modprobe ppdev

Now you should see devices like "/dev/parport0". In case you do not, you will need to create them manually and give sufficient privileges for your user:

# mknod /dev/parport0 c 99 0 -m 666

Example 1: LED trace

For this example you will need to connect 8 LEDs to Parallel interface Data port as shown below:

And then the actual script:

Code: trace.m

delay = 0.1; pp = parallel("/dev/parport0", 0); pp_data(pp, 0); pins = pow2([0, 1, 2, 3, 4, 5, 6, 7]); while 1 for p = pins pp_data(pp, p); sleep(delay); endfor # Reverse the order pins = pins(end:-1:1); endwhile pp_close(pp);

Run it and you should see LEDs "tracing" forwards and backwards.

Example 2: LED dimming a.k.a. PWM control

Use the same schematic as in Example 1.

Code: dim.m

delay = 0.00005; pp = parallel("/dev/parport0", 0); pp_data(pp, 0); dRange = 0:100; while 1 for duty = dRange pp_data(pp, 255); for dOn = 0:duty sleep(delay); endfor pp_data(pp, 0); for dOff = 0:(100-duty) sleep(delay); endfor endfor # Reverse order dRange = dRange(end:-1:1); endwhile pp_close(pp);

Run it and you should see LEDs changing brightness from lowest to maximum.

Example 3: Logic analyzer

We can surely make something more interesting, right? Enter basic logic analyzer.

Assume you are working with [this] temperature sensor. Something is not right. You do not have one of those expensive logic analyzers, but you do have a Parallel port! You remember that someone made a package for interfacing it with GNU Octave. So you connect your probes to appropriate Data port terminals and change settings accordingly. In this example:

Probe	Port terminal
!CS	DATA0
SCK	DATA1
SO	DATA2

NB: Parallel ports usually have weak pull-ups to +5V even when in "input" mode, so do not do this if unsure. One could potentially use different terminals in Control/Status ports to get true high-impedance inputs.

And write a simple script below:

Code: logic_analyzer.m

##################################################################### # Settings ##################################################################### # Channels to capture #channels = [0, 1, 2, 3, 4, 5, 6, 7]; channels = [2, 1, 0]; # Channel labels #channel = {"CH0"; "CH1"; "CH2"; "CH3"; "CH4"; "CH5"; "CH6"; "CH7"}; channel = {"SO"; "SCK"; "!CS"}; # Trigger channel triggerCh = 0; # When to trigger trigger = 0; # Capture on low. For high - 1 ##################################################################### samplesTime = []; samplesValue = []; #pp_close(pp); pp = parallel("/dev/parport0", 1); printf("Waiting for trigger...\n"); fflush(stdout); data = pp_data(pp); while (bitget(data, triggerCh + 1) != trigger) oldData = data; data = pp_data(pp); endwhile printf("Capturing...\n"); fflush(stdout); startTime = time(); samplesTime(end + 1) = 0; samplesValue(end + 1) = oldData; while (bitget(data, triggerCh + 1) == trigger) data = pp_data(pp); samplesTime(end + 1) = time() - startTime; samplesValue(end + 1) = data; endwhile # Statistics printf("Average sample rate: %f kHz\n", size(samplesValue)(2) / samplesTime(end) / 1000.0); pp_close(pp); # Plotting figure; for p = 1:size(channels)(2) subplot (size(channels)(2), 1, p) plot(samplesTime, bitget(samplesValue, channels(p) + 1)) ylabel(channel{p}); axis([-0.01, samplesTime(end)+ 0.01, -1, 2], "manual"); set(gca(), 'ytick', -1:2); set(gca(), 'yticklabel', {''; '0'; '1'; ''}); endfor xlabel ("t");

If connections and settings are correct you should see something like this:

Now you can fully debug what is going with your hardware from comfort of GNU Octave.

i2c

i2c