driver/sigrok: Add sigrok driver for DMMs

The SigrokDmmDriver wraps around a single channel DMM controlled by sigrok.
It has been tested with Unit-T UT61C and UT61B devices but probably also
works with other single chnnel DMMs.

This driver binds to a SigrokUsbDevice.
Make sure to select the correct driver for your DMM there.

Example usage:
> resources:
>   - SigrokUSBDevice:
>       driver: uni-t-ut61c
>       match:
>         'ID_PATH': pci-0000:07:00.4-usb-0:2:1.0
> drivers:
>   - SigrokDmmDriver: {}

Args:
    bindings (dict): driver to use with sigrok

Signed-off-by: Chris Fiege <[email protected]>

doc/configuration.rst

@@ -2444,6 +2444,39 @@ Arguments:
   - max_current (float): optional, maximum allowed current for protection against
     accidental damage (in ampere)
 
+SigrokDmmDriver
+~~~~~~~~~~~~~~~
+The `SigrokDmmDriver` uses a  `SigrokDevice` resource to record samples from a digital multimeter (DMM) and provides
+them during test runs.
+
+It is known to work with Unit-T `UT61B` and `UT61C` devices but should also work with other DMMs supported by *sigrok*.
+
+Binds to:
+  sigrok:
+    - `SigrokUSBDevice`_
+    - `SigrokUSBSerialDevice`_
+    - `NetworkSigrokUSBDevice`_
+    - NetworkSigrokUSBSerialDevice
+
+Implements:
+  - None yet
+
+Arguments:
+  - None
+
+Sampling can be started calling `start(samples, timeout=None)`.
+It sets up sampling and returns immediately.
+If no `timeout` is provided the timeout will be set to something reasonable.
+
+Samples can be obtained using `get_samples()`. `get_samples()` will block until either *sigrok* terminates or `timeout`
+is reached.
+This method returns a `(unit, samples)` tuple:
+`unit` is the physical unit reported by the DMM;
+samples is an iterable of samples.
+
+This driver relies on buffering of the subprocess call.
+Reading a few samples will very likely work - but obtaining a lot of samples may stall.
+
 USBSDMuxDriver
 ~~~~~~~~~~~~~~
 The :any:`USBSDMuxDriver` uses a USBSDMuxDevice resource to control a

labgrid/driver/__init__.py

@@ -23,7 +23,7 @@
 from .qemudriver import QEMUDriver
 from .modbusdriver import ModbusCoilDriver
 from .modbusrtudriver import ModbusRTUDriver
-from .sigrokdriver import SigrokDriver, SigrokPowerDriver
+from .sigrokdriver import SigrokDriver, SigrokPowerDriver, SigrokDmmDriver
 from .usbstoragedriver import USBStorageDriver, NetworkUSBStorageDriver, Mode
 from .resetdriver import DigitalOutputResetDriver
 from .gpiodriver import GpioDigitalOutputDriver

labgrid/driver/sigrokdriver.py

@@ -23,6 +23,7 @@
 from .common import Driver, check_file
 from .exception import ExecutionError
 from .powerdriver import PowerResetMixin
+from ..util import Timeout
 
 
 @attr.s(eq=False)
@@ -329,3 +330,94 @@ def measure(self):
         if len(res) != 2:
             raise ExecutionError(f"Cannot parse --show output {out}")
         return res
+
+@target_factory.reg_driver
+@attr.s(eq=False)
+class SigrokDmmDriver(SigrokCommon):
+    """
+    This driver wraps around a single channel DMM controlled by sigrok.
+    It has been tested with Unit-T UT61C and UT61B devices but probably also
+    works with other single chnnel DMMs.
+
+    This driver binds to a SigrokUsbDevice.
+    Make sure to select the correct driver for your DMM there.
+
+    Example usage:
+    > resources:
+    >   - SigrokUSBDevice:
+    >       driver: uni-t-ut61c
+    >       match:
+    >         'ID_PATH': pci-0000:07:00.4-usb-0:2:1.0
+    > drivers:
+    >   - SigrokDmmDriver: {}
+
+    Args:
+        bindings (dict): driver to use with sigrok
+    """
+    bindings = {
+        "sigrok": {SigrokUSBSerialDevice, NetworkSigrokUSBSerialDevice, SigrokUSBDevice, NetworkSigrokUSBDevice},
+    }
+
+    @Driver.check_active
+    @step(result=True)
+    def start(self, samples, timeout=None):
+        """
+        Starts to read samples from the DMM.
+        This function returns once sampling has been started. Sampling continues in the background.
+
+        Note: We use subprocess.PIPE to buffer the samples. When this buffer is too small for the number of
+        sampled requested sampling may stall.
+
+        Args:
+            samples: Number of samples to obtain
+            timeout: Timeout after which sampling should be stopped.
+                     If None: timemout[s] = samples * 1s + 5s
+                     If int: Timeout in [s]
+
+        Returns: None
+        """
+        if not timeout:
+            timeout = samples + 5.0
+
+        args = f"-O csv --samples {samples}".split(" ")
+        self._call_with_driver(*args)
+        self._timeout = Timeout(timeout)
+        self._running = True
+
+    @Driver.check_active
+    @step(result=True)
+    def get_samples(self):
+        """
+        Waits for sigrok to complete and returns all samples obtained afterwards.
+        This function blocks until either sigrok has terminated or the timeout has been reached.
+
+        Returns:
+            (unit_spec, [sample, ...])
+        """
+        if not self._running:
+            raise RuntimeError("Capture was not started before get_samples was called.")
+        while not self._timeout.expired:
+            if self._process.poll() is not None:
+                # process has finished. no need to wait for the timeout
+                break
+            time.sleep(0.1)
+        else:
+            # process did not finish in time
+            self.log.info("sigrok-cli did not finish in time, increase timeout?")
+            self._process.kill()
+
+        res = []
+        unit = ""
+        for line in self._process.stdout.readlines():
+            line = line.strip()
+            if b';' in line:
+                # discard header information
+                continue
+            if not unit:
+                # the first line after the header contains the unit information
+                unit = line.decode()
+            else:
+                # all other lines are actual values
+                res.append(float(line))
+        self._process.communicate()
+        return unit, res