configure: Hameg HMO does not strictly depend on serial communication

[libsigrok.git] / README.devices

-------------------------------------------------------------------------------
README.devices
-------------------------------------------------------------------------------

This README contains various notes for users of libsigrok (or frontends
that are based on libsigrok) about device- and/or driver-specific issues.


Firmware
--------

Some devices supported by libsigrok need a firmware to be uploaded every time
the device is connected to the PC (usually via USB), before it can be used.

The default locations where libsigrok expects the firmware files are:

  $SIGROK_FIRMWARE_DIR (environment variable)
  $HOME/.local/share/sigrok-firmware
  $prefix/share/sigrok-firmware
  /usr/local/share/sigrok-firmware
  /usr/share/sigrok-firmware

($prefix is usually /usr/local or /usr, depending on your ./configure options)

For further information see the section below and also:

  http://sigrok.org/wiki/Firmware


Per-driver firmware requirements
--------------------------------

The following drivers/devices require a firmware upload upon connection:

 - asix-omega-rtm-cli: There is no native sigrok support for ASIX OMEGA
   devices. But the vendor's RTM CLI application can be used in streaming
   mode, which transparently handles the device detection and firmware
   download. The firmware ships with the vendor application. See below
   for details how to make the vendor application available to the sigrok
   driver.

 - asix-sigma: The ASIX SIGMA and SIGMA2 require various firmware files,
   depending on the settings used. These files are available from our
   'sigrok-firmware' repository/project under a license which allows us
   to redistribute them.

 - dreamsourcelab-dslogic: The DreamSourceLab DSLogic/DSCope device series
   requires various firmware files and FPGA bitstream files.
   These can be extracted/downloaded from the vendor's GitHub repo using a
   tool from our 'sigrok-util' repository/project.

 - fx2lafw: Logic analyzers based on the Cypress FX2(LP) chip need the
   firmware files from the 'sigrok-firmware-fx2lafw' repository/project.
   The firmware is written from scratch and licensed under the GNU GPLv2+.

 - hantek-6xxx: Certain oscilloscopes based on the Cypress FX2(LP) chip, such
   as the Hantek 6022BE/6022BL, SainSmart DDS120, and Rocktech BM102, need the
   firmware files from the 'sigrok-firmware-fx2lafw' repository/project.
   The firmware is written from scratch and licensed under the GNU GPLv2+.

 - hantek-dso: The Hantek DSO-2090 (and other supported models of the same
   series of Hantek PC oscilloscopes) need firmware files.
   These can be extracted from the vendor's Windows drivers using a tool
   from our 'sigrok-util' repository/project.

 - lecroy-logicstudio: The LeCroy LogicStudio requires FPGA bitstream files.
   These can be extracted from the vendor's Windows software using a tool
   from our 'sigrok-util' repository/project.
   Additionally, it requires a Cypress FX2 firmware. This can be extracted
   from the vendor's Windows software using another tool. Details:

     http://sigrok.org/wiki/LeCroy_LogicStudio#Firmware

 - saleae-logic16: The Saleae Logic16 needs a firmware file for the
   Cypress FX2 chip in the device, as well as two FPGA bitstream files.
   These can be extracted from the vendor's Linux application using a tool
   from our 'sigrok-util' repository/project.

 - saleae-logic-pro: The Saleae Logic Pro 16 needs a firmware file for the
   Cypress FX3 chip in the device, as well as an FPGA bitstream file.
   These can be extracted from the vendor's Linux application using a tool
   from our 'sigrok-util' repository/project.

 - sysclk-lwla:

    - The Sysclk LWLA1034 requires various bitstream files.
      These files are available from our 'sigrok-firmware' repository/project
      under a license which allows us to redistribute them.

    - The Sysclk LWLA1016 requires various bitstream files.
      These can be extracted from the vendor's Windows drivers using a tool
      from our 'sigrok-util' repository/project.

 - sysclk-sla5032: The Sysclk SLA5032 needs an FPGA bitstream file.
   This file can be copied (and renamed) from the Windows vendor software
   installation directory. Details:

     https://sigrok.org/wiki/Sysclk_SLA5032#Firmware

The following drivers/devices do not need any firmware upload:

 - agilent-dmm
 - appa-55ii
 - arachnid-labs-re-load-pro
 - atten-pps3xxx
 - baylibre-acme
 - beaglelogic
 - cem-dt-885x
 - center-3xx (including all subdrivers)
 - chronovu-la
 - colead-slm
 - conrad-digi-35-cpu
 - demo
 - fluke-45
 - fluke-dmm
 - ftdi-la
 - gmc-mh-1x-2x (including all subdrivers)
 - gwinstek-gds-800
 - gwinstek-gpd
 - hameg-hmo
 - hantek-4032l
 - hp-3457a
 - hp-3478a
 - hung-chang-dso-2100
 - ikalogic-scanalogic2
 - ikalogic-scanaplus
 - ipdbg-la
 - kecheng-kc-330b
 - kern-scale
 - korad-kaxxxxp
 - lascar-el-usb
 - lecroy-xstream
 - link-mso19
 - manson-hcs-3xxx
 - maynuo-m97
 - mic-985xx (including all subdrivers)
 - microchip-pickit2
 - mooshimeter-dmm
 - motech-lps-30x
 - norma-dmm
 - openbench-logic-sniffer
 - pce-322a
 - pipistrello-ols
 - rdtech-dps
 - rigol-dg
 - rigol-ds
 - rohde-schwarz-sme-0x
 - scpi-dmm
 - scpi-pps
 - serial-dmm (including all subdrivers)
 - serial-lcr (including all subdrivers)
 - siglent-sds
 - teleinfo
 - testo
 - tondaj-sl-814
 - uni-t-dmm (including all subdrivers)
 - uni-t-ut32x
 - yokogawa-dlm
 - zeroplus-logic-cube
 - zketech-ebd-usb


Specifying serial ports
-----------------------

Many devices supported by libsigrok use serial port based cables (real RS232
or USB-to-serial ones, CDC class) to connect to a PC. These serial cables are
supported by the libserialport library. Some vendors prefer to use HID chips
instead of CDC chips in their serial cables. These cables can get supported
by means of the hidapi library. Note that each chip type requires specific
support in the libsigrok library. Bluetooth connected devices may be supported
as well when they communicate by means of RFCOMM channels, or one of the
implemented BLE notification/indication approaches, and one of the Bluetooth
supporting platforms is used.

For all these devices, you need to specify the serial port they are connected
to (e.g. using the 'conn' option in sigrok-cli). It is not possible to scan
for such devices without specifying a serial port.

Example:

 $ sigrok-cli --driver <somedriver>:conn=/dev/ttyUSB0 ...
 $ sigrok-cli --driver <somedriver>:conn=hid/cp2110 ...
 $ sigrok-cli --driver <somedriver>:conn=bt/rfcomm/01-23-45-67-89-ab ...

Formal syntax for serial communication:

 - COM ports (RS232, USB CDC):
   conn=<com-port>
 - USB HID cables:
   conn=hid[/<chip>]
   conn=hid[/<chip>]/usb=<bus>.<dev>[.<if>]
   conn=hid[/<chip>]/raw=<path>
   conn=hid[/<chip>]/sn=<serno>
   conn=hid[/<chip>]/iokit=<path>
   chip can be: bu86x, ch9325, cp2110, victor
   path may contain slashes
   path and serno are "greedy" (span to the end of the spec)
 - Bluetooth Classic and Bluetooth Low Energy (BLE):
   conn=bt/<conn>/<addr>
   conn can be: rfcomm, ble122, nrf51, cc254x
   addr can be "dense" or separated, bt/cc254x/0123456789ab or
     bt/rfcomm/11-22-33-44-55-66 or bt/ble122/88:6b:12:34:56:78
     (note that colons may not be available when the conn= spec is taken
     from a string that separates fields by colon, e.g. in the "--driver
     <name>:conn=<spec>" example, that is why the dense form and the use
     of dashes for separation are supported)

Some of the drivers implement a default for the connection. Some of the
drivers can auto-detect USB connected devices.

Beyond strict serial communication over COM ports (discussed above), the
conn= property can also address specific USB devices, as well as specify TCP
or VXI communication parameters. See these examples:

 $ sigrok-cli --driver <somedriver>:conn=<vid>.<pid> ...
 $ sigrok-cli --driver <somedriver>:conn=tcp-raw/<ipaddr>/<port> ...
 $ sigrok-cli --driver <somedriver>:conn=vxi/<ipaddr> ...
 $ sigrok-cli --driver <somedriver>:conn=usbtmc/<bus>.<addr> ...

Individual device drivers _may_ implement additional semantics for the
conn= specification, which would not apply to other drivers, yet can be
rather useful for a given type of device.

 $ sigrok-cli --driver <somedriver>:conn=sn=<serno>


Specifying serial port parameters
---------------------------------

Every serial device's driver has default serial port parameters like baud
rate, number of data bits, stop bits and handshake status. If a device requires
different parameters, pass them as option "serialcomm" with the driver name.
See libsigrok docs for the function serial_set_paramstr() for complete specs.

Example:

 $ sigrok-cli --driver <somedriver>:conn=<someconn>:serialcomm=9600/7n1/dtr=1


Permissions of serial port based devices
----------------------------------------

When using devices supported by libsigrok that use serial port based cables
(real RS232 or USB-to-serial ones) to connect to a PC, you need to ensure
that the user running the libsigrok frontend has (read/write) permissions to
access the serial port device (e.g. /dev/ttyS0, /dev/ttyUSB0, and so on).

You can use 'chmod' to apply permissions as you see fit, and/or 'chown' to
change the owner of the serial port device to a certain user or group.

For USB-to-serial based devices, we recommended using our udev rules file
(see below for details).


Permissions for USB devices (udev rules files)
----------------------------------------------

When using USB-based devices supported by libsigrok, the user running the
libsigrok frontend (e.g. sigrok-cli) has to have (read/write) permissions
for the respective USB device.

On Linux, this is accomplished using udev rules. libsigrok ships a rules
file containing all supported devices which can be detected reliably
(generic USB-to-serial converters are omitted, as these are used for a wide
range of devices, e.g. GPS receivers, which are not handled by libsigrok).

The file is available in contrib/60-libsigrok.rules. This file just contains
the list of devices and flags these devices with ID_SIGROK="1". Access is
granted by the 61-libsigrok-plugdev.rules or 61-libsigrok-uaccess.rules files,
allowing access to members of the plugdev group or to currently logged in
users, respectively.

When using a libsigrok package from your favorite Linux distribution, the
files should already be installed in /usr/lib/udev/rules.d/, i.e.
60-libsigrok.rules and one of the access granting rules files. Use of
61-libsigrok-uaccess.rules is encouraged on systemd distributions.

The access policy can be locally overridden by placing appropriate rules in
/etc/udev/rules.d/, disabling or ammending the default policy. See the
udev documentation, e.g. man 7 udev, for details.

If you're building from source, you need to copy the file to the place
where udev will read these rules. Local rules should go to /etc/udev/rules.d.
Keep the file naming, otherwise interaction between the libsigrok rules and
rules shipped by the system will be broken.

Please consult the udev docs for details.


Non-default drivers for commodity chips
---------------------------------------

Some vendors include common USB chips in their products yet assign device
specific VID:PID pairs. Which results in the necessity for extra steps
before the serial port can be used:

- GW Instek VCP, found in GDM-8000 and probably other meters: Install the
  vendors Windows driver to get access to a COM port. Or force the driver
  assignment on Linux:
    # modprobe cp210x
    # echo 2184 0030 > /sys/bus/usb-serial/drivers/cp210x/new_id


Cypress FX2 based devices
-------------------------

Devices using the Cypress FX2(LP) chip without any specific USB VID/PID will
be enumerated with VID/PID 04b4:8613 (the default for "unconfigured FX2").
These are usually "FX2 eval boards" (that can also be used as LAs, though).

On Linux, the 'usbtest' driver will usually grab such devices, and they will
thus not be usable by libsigrok (and frontends).

You can fix this by running 'rmmod usbtest' as root before using the device.


UNI-T DMM (and rebranded models) cables
---------------------------------------

UNI-T multimeters (and rebranded devices, e.g. some Voltcraft models) can
ship with different PC connectivity cables:

 - UT-D02 (RS232 cable)
 - UT-D04 (USB/HID cable with Hoitek HE2325U chip, USB VID/PID 04fa:2490)
 - UT-D04 (USB/HID cable with WCH CH9325 chip, USB VID/PID 1a86:e008)
 - UT-D07 (Bluetooth adapter, ISSC BL79 BLETR chip)
 - UT-D09 (USB/HID cable with SiL CP2110 chip, USB VID/PID 10c4:ea80)

The above cables are all physically compatible (same IR connector shape)
with all/most currently known UNI-T multimeters. For example, you can
use either of the UT-D04 USB/HID cables or the UT-D02 RS232 cable with
the UNI-T UT61D multimeter.

When using the UT-D02 RS232 cable with any of the supported UNI-T DMMs,
you have to use the respective driver with a '-ser' drivername suffix
(internally all of these models are handled by the 'serial-dmm' driver).

You also need to specify the serial port via the 'conn' option, e.g.
/dev/ttyUSB0 (attached via a USB-to-serial cable) or /dev/ttyS0 (actual
RS232 port) on Linux (see above).

Finally, the user running the frontend (e.g. sigrok-cli) also needs
permissions to access the respective serial port (see above).

Examples (sigrok-cli):

 $ sigrok-cli --driver uni-t-ut61e-ser:conn=/dev/ttyUSB0 ...
 $ sigrok-cli --driver voltcraft-vc820-ser:conn=/dev/ttyS0 ...

When using any of the UT-D04 USB/HID cables you have to use the respective
driver _without_ the '-ser' drivername suffix (internally all of these models
are handled by the 'uni-t-dmm' driver).

You also need to specify the USB vendor/device IDs of the cable.
Autodetection is not possible here, since various other products use the
USB VID/PID of those cables too, and there is no way to distinguish them.

Since the UT-D04 cables are USB based (but don't use a USB-to-serial chip)
there is no need to specify a serial port via 'conn', of course.
However, the user running the frontend does also need to have permissions
to access the respective USB device (see above).

Examples (sigrok-cli):

 $ sigrok-cli --driver uni-t-ut61e:conn=1a86.e008 ...
 $ sigrok-cli --driver voltcraft-vc820:conn=04fa.2490 ...


UNI-T UT-D04 cable issue on Linux
---------------------------------

The UNI-T UT-D04 cable with Hoitek HE2325U (or WCH CH9325) chip seems to have
a very specific problem on Linux. Apparently it requires to be put into
suspend (and woken up again) before it is usable. This seems to be a
Linux-only issue, Windows is not affected by this since apparently the
Windows kernel does this for every USB device, always.

Thus, if you want to use any of the UNI-T DMMs with this specific cable,
you'll have to run the following script (as root) once, every time you attach
the cable via USB. The script was written by Ralf Burger.

See also: http://erste.de/UT61/index.html

  #!/bin/bash
  for dat in /sys/bus/usb/devices/*; do
    if test -e $dat/manufacturer; then
      grep "WCH.CN" $dat/manufacturer > /dev/null && echo auto > ${dat}/power/level && echo 0 > ${dat}/power/autosuspend
    fi
  done


Enabling multimeter / data logger measurement output
----------------------------------------------------

Some multimeters or data loggers will not start outputting measurement data
unless a certain action has been performed by the user beforehand. This is
usually mentioned in the vendor manual of the respective device, but here's
a short list for convenience:

 - BBC Goertz Metrawatt M2110: Briefly press the "Start/Reset" button on the
   interface panel on top.
 - Brymen BM257s: Press HOLD during power-on.
 - Digitek DT4000ZC: Briefly press the "RS232" button.
 - EEVBlog 121GW: Hold "1ms PEAK" until the "BT" indicator is shown.
 - ES51919 based LCR meters (DER EE DE-5000, PeakTech 2170, UNI-T UT612):
   Press the button with the "RS232" or "USB" or "PC link" label (usually
   the "up" cursor button).
 - Gossen Metrawatt Metrahit 1x/2x devices, driver gmc-mh-1x-2x-rs232:
   - Power on the device with the "DATA" button pressed.
   - Metrahit 2x devices must be configured for the respective interface type.
 - Gossen Metrawatt Metrahit 2x devices, driver gmc-mh-2x-bd232:
   - 'BD232' interface:
      The multimeter must be configured for the respective interface type.
   - 'SI232-II' interface ("PC Mode"):
      The multimeter must be configured for interface type 'BD232' (all),
      'SI232 online' (28-29S) or 'SI232 store' (22-26x). The interface must
      be configured to the same baud rate as the host (default 9600).
      Multimeter and interface must be configured to the same address.
 - GW Instek GDM-397: Press the "REL/RS232C (USB)" button for roughly 1 second.
 - GW Instek VCP: See the discussion on manual driver assignment to common
   USB to UART chips with non-default USB identification.
 - MASTECH MS6514: Press the "Setup/PC-Link" button for roughly 3 seconds.
 - Meterman 38XR: Press the "RS232" button.
 - Metrix MX56C: Press the PRINT button to have the meter send acquisition
   data via IR. Hold the PRINT button to adjust the meter's transmission
   interval.
 - Norma DM950: If the interface doesn't work (e.g. USB-RS232 converter), power
   on the device with "FUNC" pressed (to power the interface from the DMM).
 - PCE PCE-DM32: Briefly press the "RS232" button.
 - RadioShack 22-812: Press and hold "SELECT" and "RANGE" together.
 - TekPower TP4000ZC: Briefly press the "RS232" button.
 - Tenma 72-7750: Briefly press the "RS232C" button.
 - UNI-T UT60G: Briefly press the "RS232C" button.
 - UNI-T UT61B/C/D: Press the "REL/RS232/USB" button for roughly 1 second.
 - UNI-T UT71x: Press the "SEND/-/MAXMIN" button for roughly 1 second.
   Briefly pressing the "EXIT" button leaves this mode again.
 - UNI-T UT181A: In the "SETUP" menu set "Communication" to "ON".
 - UNI-T UT325: Briefly press the "SEND" button (as per manual). However, it
   appears that in practice you don't have to press the button (at least on
   some versions of the device), simply connect the device via USB.
 - V&A VA18B/VA40B: Keep the "Hz/DUTY" key pressed while powering on the DMM.
 - Victor 70C/86C: Press the "REL/RS232" button for roughly 1 second.
 - Voltcraft VC-830: Press the "REL/PC" button for roughly 2 seconds.
 - Voltcraft VC-870: Press the "REL/PC" button for roughly 1 second.


ASIX OMEGA in RTM CLI mode
--------------------------

The asix-sigma driver can detect the Omega devices' presence, but does
not support their protocol and emits a diagnostics message. The firmware
image is not available for distribution, and information on the protocol
is not available. That's why native support is in some distant future.
Yet basic operation of Omega devices is available by using the vendor's
command line application for real time mode (RTM CLI).

The vendor application targets Windows (on x86), but also executes on
Linux when 32bit libraries for FTDI communication are provided. The
user manual discusses the installation. The sigrok asix-omega-rtm-cli
driver uses the vendor provided omegartmcli.exe binary to configure the
device for streaming, and to acquire sample data.

Either make an "omegartmcli" executable available in PATH. This can be
the vendor's executable or some wrapper around it or a symlink to it.
Or specify the executable's location in the OMEGARTMCLI environment
variable. The sigrok driver accepts an optional serial number (six or
eight hex digits) to select one out of several connected devices.

  (optional)
  $ export "OMEGARTMCLI=$HOME/.wine/drive_c/progx86/ASIX/SIGMA/omegartmcli.exe"

  (optional)
  $ OMEGASN=":conn=sn=a6030123"

  (example use)
  $ sigrok-cli -d asix-omega-rtm-cli${OMEGASN} --show
  $ sigrok-cli -d asix-omega-rtm-cli${OMEGASN} -o capture.sr --time 10s
  $ sigrok-cli -d asix-omega-rtm-cli${OMEGASN} -o capture.sr --samples 100m
  $ pulseview  -d asix-omega-rtm-cli${OMEGASN}

The RTM mode of operation samples 16 channels at a fixed rate of 200MHz.
Hardware triggers are not available in this mode. Glib should handle
platform specific details of external process execution, but the driver
was only tested on Linux so far. Acquisition start in sigrok applications
may take some time before sample data becomes available (roughly one
second here on a slow machine). This is an implementation detail of the
RTM CLI approach including execution under wine.

The reliability of that setup in the presence of fast changing input
signals is yet to get determined. It's assumed that slow input signals
are operational. It's essential that the _average_ rate of changes in
the input signal in combination with the hardware compression are such
that the FTDI FIFO can communicate all involved data via USB2.0 to the
application. Intermediate bursts of rapid changes shall not be an issue
given the Omega devices' deep memory which RTM uses for buffering.

Native support for the Asix Omega devices depends on the availability of
a protocol description and use of the protocol depends on the firmware's
availability at the user's site. Which then would allow to capture to
DRAM at high rates without the communication bottleneck, before the data
gets communicated to the PC after the acquisition has completed. Compare
the native sigrok support for Asix Sigma.


ChronoVu LA8/LA16 USB VID/PIDs
------------------------------

The ChronoVu LA8/LA16 logic analyzer is available in two revisions. Previously,
the device shipped with a USB VID/PID of 0403:6001, which is the standard ID
for FTDI FT232 USB chips.

Since this made it hard to distinguish the LA8/LA16 from any other device
with this FTDI chip connected to the PC, the vendor later shipped the
device with a USB VID/PID of 0403:8867.

The 'chronovu-la' driver in libsigrok supports both VID/PID pairs and
automatically finds devices with either VID/PID pair.


OLS
---

The Dangerous Prototypes Openbench Logic Sniffer (OLS) logic analyzer
driver in libsigrok assumes a somewhat recent firmware has been flashed onto
the OLS (it doesn't need a firmware upload every time it's attached via USB,
since the firmware is stored in the device permanently).

The most recent firmware version that is tested is 3.07.

If you use any older firmware and your OLS is not found or is not working
properly, please upgrade to at least this firmware version. Check the
Dangerous Prototypes wiki for firmware upgrade instructions:

 http://dangerousprototypes.com/docs/Logic_Sniffer_upgrade_procedure

Also, you need to specify a serial port for the OLS in the frontends, e.g.
using the 'conn' option in sigrok-cli, and you also need to have the
permissions to access the serial port (see above).

Example:

 $ sigrok-cli --driver ols:conn=/dev/ttyACM0 ...


JTAGulator
----------

The Grand Idea Studio JTAGulator also implements the SUMP protocol and
thus is covered by the OLS driver. See the vendor's wiki on details how
to enable the Logic Analyzer mode of operation.

  https://github.com/grandideastudio/jtagulator/wiki/Logic-Analyzer


Mooshimeter
-----------

The Mooshim Engineering Mooshimeter is controlled via Bluetooth Low Energy
(sometimes called Bluetooth 4.0), as such it requires a supported Bluetooth
interface available. The 'conn' option is required and must contain the
Bluetooth MAC address of the meter.

Example:

  $ sigrok-cli --driver mooshimeter-dmm:conn=12-34-56-78-9A-BC ...

Since the Mooshimeter has no physical interface on the meter itself, the
channel configuration is set with the 'channel_config' option. The format
of this option is 'CH1,CH2' where each channel configuration has the form
'MODE:RANGE:ANALYSIS', with later parts being optional. In addition for
CLI compatibility, the ',' in the channels can also be a '/' and the ':' in
the individual configuration can be a ';'.

Available channel 1 modes:

  - Current, A: Current in amps
  - Temperature, T, K: Internal meter temperature in Kelvin
  - Resistance, Ohm, W: Resistance in ohms
  - Diode, D: Diode voltage
  - Aux, LV: Auxiliary (W input) low voltage sensor (1.2V max)

Available channel 2 modes:

  - Voltage, V: Voltage
  - Temperature, T, K: Internal meter temperature in Kelvin
  - Resistance, Ohm, W: Resistance in ohms
  - Diode, D: Diode voltage
  - Aux, LV: Auxiliary (W input) low voltage sensor (1.2V max)

Only one channel can use the shared inputs at a time (e.g. if CH1 is measuring
resistance, CH2 cannot measure low voltage). Temperature is excepted from
this, so the meter can measure internal temperature and low voltage at the
same time.

Additionally, the meter can calculate the real power of both channels. This
generally only makes sense when CH1 is set to current and CH2 is set to a
voltage and so it is disabled by default. It must be enabled by enabling the
'P' channel (the third channel).

The range of the channel specification sets the maximum input for that channel
and is rounded up to the next value the meter itself supports. For example,
specifying 50 for the voltage will result in the actual maximum of 60.
Specifying 61 would result in 600. If omitted, sigrok will perform
auto-ranging of the channel by selecting the next greater value than the
latest maximum.

The analysis option sets how the meter reports its internal sampling buffer
to sigrok:

 - Mean, DC: The default is a simple arithmetic mean of the sample buffer
 - RMS, AC: The root mean square of the sample buffer
 - Buf, Buffer, Samples: Report the entire sample buffer to sigrok. This
   results in packets that contain all the samples in the buffer instead
   of a single output value.

The size of the sample buffer is set with the 'avg_samples' option, while
the sampling rate is set with the 'samplerate' option. So the update rate
is avg_samples/samplerate. Both are rounded up to the next supported value
by the meter.

Example:

  $ sigrok-cli -c channel_config="Aux;0.1/T" --driver mooshimeter-dmm...
  $ sigrok-cli -c channel_config="A;;AC/V;;AC" --driver mooshimeter-dmm...