# FAQ¶

## How do I ...¶

### find ARTIQ examples?¶

The examples are installed in the examples folder of the ARTIQ package. You can find where the ARTIQ package is installed on your machine with:

python3 -c "import artiq; print(artiq.__path__[0])"


Copy the examples folder from that path into your home/user directory, and start experimenting!

### prevent my first RTIO command from causing an underflow?¶

The first RTIO event is programmed with a small timestamp above the value of the timecounter when the core device is reset. If the kernel needs more time than this timestamp to produce the event, an underflow will occur. You can prevent it by calling break_realtime just before programming the first event, or by adding a sufficient delay.

If you are not resetting the core device, the time cursor stays where the previous experiment left it.

### organize datasets in folders?¶

Use the dot (”.”) in dataset names to separate folders. The GUI will automatically create and delete folders in the dataset tree display.

### write a generator feeding a kernel feeding an analyze function?¶

Like this:

def run(self):
self.parse(self.pipe(iter(range(10))))

def pipe(self, gen):
for i in gen:
r = self.do(i)
yield r

def parse(self, gen):
for i in gen:
pass

@kernel
def do(self, i):
return i


### create and use variable lengths arrays in kernels?¶

Don’t. Preallocate everything. Or chunk it and e.g. read 100 events per function call, push them upstream and retry until the gate time closes.

### execute multiple slow controller RPCs in parallel without losing time?¶

Use threading.Thread: portable, fast, simple for one-shot calls.

### write part of my experiment as a coroutine/asyncio task/generator?¶

You can not change the API that your experiment exposes: build(), prepare(), run() and analyze() need to be regular functions, not generators or asyncio coroutines. That would make reusing your own code in sub-experiments difficult and fragile. You can however wrap your own generators/coroutines/tasks in regular functions that you then expose as part of the API.

### determine the pyserial URL to attach to a device by its serial number?¶

You can list your system’s serial devices and print their vendor/product id and serial number by running:

\$ python3 -m serial.tools.list_ports -v


It will give you the /dev/ttyUSBxx (or the COMxx for Windows) device names. The hwid: field gives you the string you can pass via the hwgrep:// feature of pyserial serial_for_url() in order to open a serial device.

The preferred way to specify a serial device is to make use of the hwgrep:// URL: it allows to select the serial device by its USB vendor ID, product ID and/or serial number. Those never change, unlike the device file name.

See the TDC001 documentation for an example of hwgrep:// usage.

### run unit tests?¶

The unit tests assume that the Python environment has been set up in such a way that import artiq will import the code being tested, and that this is still true for any subprocess created. This is not the way setuptools operates as it adds the path to ARTIQ to sys.path which is not passed to subprocesses; as a result, running the tests via setup.py is not supported. The user must first install the package or set PYTHONPATH, and then run the tests with e.g. python3 -m unittest discover in the artiq/test folder and lit . in the artiq/test/lit folder.

For the hardware-in-the-loop unit tests, set the ARTIQ_ROOT environment variable to the path to a device database containing the relevant devices.

The core device tests require the following TTL devices and connections:

• ttl_out: any output-only TTL.
• ttl_out_serdes: any output-only TTL that uses a SERDES (i.e. has a fine timestamp). Can be aliased to ttl_out.
• loop_out: any output-only TTL. Must be physically connected to loop_in. Can be aliased to ttl_out.
• loop_in: any input-capable TTL. Must be physically connected to loop_out.
• loop_clock_out: a clock generator TTL. Must be physically connected to loop_clock_in.
• loop_clock_in: any input-capable TTL. Must be physically connected to loop_clock_out.

If TTL devices are missing, the corresponding tests are skipped.