Add user manual

To enable SSH, login on console and run "puzzle-sshcfg enable"

README.md

@@ -27,7 +27,7 @@ PuzzleFW has the following features:
 
 Further details about the firmware are in these documents:
 
-- User manual, to be written
+- [User manual](doc/user_manual.md)
 - Developer manual, including the build procedure, to be written
 - [FPGA firmware description](doc/fpga_firmware.md)
 

doc/fpga_firmware.md

@@ -1,6 +1,11 @@
+---
+gitea: none
+include_toc: true
+---
+
 # PuzzleFW FPGA firmware
 
-The PuzzleFW firmware provides the following functionality:
+The FPGA firmware provides the following functionality:
 
 * Collect ADC samples at 125 MSa/s with configurable decimation or averaging.
 * Trigger on external digital input and collect a configurable number of samples.
@@ -12,7 +17,7 @@ The PuzzleFW firmware provides the following functionality:
 
 LED0 to LED7 are the first 8 yellow LEDs from left to right on the side of the Red Pitaya.
 
-LED0 blinks at a rate of 1 Hz when the PuzzleFW firmware is active.
+LED0 blinks at a rate of 1 Hz when the FPGA firmware is active.
 Its purpose is to provide a minimal indication that the FPGA is active.
 
 LED1 is on when the analog acquisition chain is enabled (register `ACQUISITION_EN`).
@@ -213,10 +218,8 @@ It marks the point in the message sequence where an unknown number of messages h
 # Timetagger
 
 The timetagger has 4 digital input signals.
-If a rising or falling edge occurs on one of these signals, a timestamp is assigned to that event and a message is emitted and transferred via DMA.
-
-A 4-cycle glitch filter is applied to the digital input signals.
-This filter rejects digital pulses shorter than 4 clock cycles (32 ns).
+If a rising or falling edge occurs on one of these signals, a timestamp is assigned to that event.
+Timestamped event messages are transferred via DMA.
 
 Messages are only emitted for _enabled_ event types.
 Rising edges and falling edges can be separately enabled or disabled for each digital input channel.
@@ -226,6 +229,14 @@ The messages are queued in a FIFO buffer inside the FPGA before being transferre
 This FIFO is necessary to hold messages for a short time while the DMA engine sets up a DMA transfer.
 It has room for 4096 messages.
 
+## Digital input signals
+
+The 4 digital input channels are connected to the digital I/O connector of the Red Pitaya.
+Digital input channels 0 to 3 correspond to pins `DIO0_P` to `DIO3_P`.
+
+A 4-cycle glitch filter is applied to the digital input signals.
+This filter rejects digital pulses shorter than 4 clock cycles (32 ns).
+
 ## Output data format
 
 The output from the timetagger is a sequence of 64-bit messages.
@@ -926,7 +937,7 @@ Therefore, the smallest unit of data transferred via DMA is a 64-bit word.
 The size of every DMA transfer is a multiple of 8 bytes, and the address of every transfer is aligned to a multiple of 8 bytes.
 
 (This is an implementation choice in the firmware.
-It is possible in principle to transfer smaller amounts of data via the AXI bus, but the PuzzleFW firmware is designed to transfer 64-bit words in all cases.)
+It is possible in principle to transfer smaller amounts of data via the AXI bus, but this firmware is designed to transfer 64-bit words in all cases.)
 
 Data are temporarily queued in a FIFO RAM block inside the FPGA until the DMA engine is ready to start a transfer.
 This is necessary because DMA operates in bursts, and it may take some time before the DMA engine can initiate a burst.

doc/remote_control.md

@@ -102,8 +102,8 @@ In the response string, such data elements are separated by space characters.
 | `AIN:CHANNELS:COUNT?`     | Number of input channels. |
 | `AIN:CHANNELS:ACTIVE`     | Number of active input channels. |
 | `AIN:CHn:RANGE`           | Analog input range. |
-| `AIN:CHn:OFFSET[:LO|HI]`  | Offset calibration. |
-| `AIN:CHn:GAIN[:LO|HI]`    | Gain calibration. |
+| `AIN:CHn:OFFSET`          | Offset calibration. |
+| `AIN:CHn:GAIN`            | Gain calibration. |
 | `AIN:CAL:SAVE`            | Save calibration. |
 | `AIN:CHn:SAMPLE[:RAW]?`   | Read ADC sample. |
 | `AIN:CHn:MINMAX[:RAW]?`   | Read ADC range monitor. |

doc/user_manual.md

@@ -0,0 +1,733 @@
+---
+gitea: none
+include_toc: true
+---
+
+# PuzzleFW User Manual
+
+PuzzleFW is an alternative, unofficial firmware package for the Red Pitaya.
+It consists of FPGA firmware and embedded software.
+The embedded software runs under Linux on the ARM processor in the Zynq.
+
+The PuzzleFW firmware does not provide a built-in user interface.
+It does not have a web interface, nor any other kind of graphical interface.
+The only way to control the system is via the network, using a remote command protocol.
+
+In typical cases, you would design custom PC software that connects to the Red Pitaya via the network to send commands and receive data.
+Such software can then present the measured data on the PC in any way it wants, possibly via a custom graphical user interface.
+
+
+## Analog input operation
+
+The analog input subsystem captures ADC samples.
+Depending on various configuration settings, the ADC samples are processed and ultimately transferred via the network.
+
+### Analog input signals
+
+A standard Red Pitaya STEMlab 125-14 has 2 analog input channels,
+sampled by one dual-input ADC.
+The analog inputs are labeled as channel 1 and channel 2.
+
+A Red Pitaya STEMlab 125-14 4-input has 4 analog input channels,
+sampled by a pair of dual-input ADCs.
+The analog inputs are labeled as channel 1 to channel 4.
+On a 4-input system, the firmware can operate either in 2-channel mode or
+in 4-channel mode.
+In 2-channel mode, only samples from channel 1 and channel 2 are processed.
+
+### Sampling
+
+All analog input channels are simultaneously sampled at a fixed
+sample rate of 125 MSa/s.
+
+Samples are unsigned 14-bit integers.
+An input level of 0 Volt corresponds to the middle of the 14-bit range,
+i.e. approximately 8192.
+Since the Red Pitaya uses an inverting input circuit.
+positive input voltages correspond to lower ADC codes,
+and negative input voltages correspond to higher ADC codes.
+
+### Downsampling (decimation)
+
+The ADCs operate at a fixed sample rate of 125 MSa/s.
+While the sample rate of the ADC can not be changed, the effective sample rate can be reduced by digital processing in the FPGA.
+
+The effective sample rate after digital processing is equal to the ADC sample rate divided by the _sample rate divisor_ (also called _downsample factor_ or _decimation factor_).
+The sample rate divisor is always an integer.
+Setting the sample rate divisor to 1 results in an effective sample rate equal to the ADC sample rate, i.e. 125 MSa/s.
+Setting a higher sample rate divisor reduces the effective sample rate to `125000000 / divisor` samples per second.
+The maximum supported sample rate divisor is 2<sup>18</sup>, corresponding to
+an effective sample rate of approximately 477 samples/s.
+
+Rather than configuring the sample rate divisor, the system also supports configuring an effective sample rate in samples per second.
+In this case, the requested sample rate is converted to the corresponding sample rate divisor and rounded to the nearest integer.
+
+The system supports two modes of sample rate reduction: decimation and averaging.
+In decimation mode with sample rate divisor _N_, only the first sample out of every group of _N_ samples is processed, and the remaining _N_ - 1 samples are discarded.
+Decimation causes high frequency signals (above the Nyquist frequency) to alias into the downsampled data.
+
+In averaging mode, the system calculates the sum of each group of _N_ samples.
+Averaging mode has the advantage that it suppresses aliasing and noise.
+For this reason, averaging mode is the default setting.
+
+Averaging mode is implemented by summing sample values.
+This causes an effective gain factor that depends on the sample rate divisor:
+if _N_ samples are summed, the result is equal to _N_ times the average
+sample value.
+If the sample rate divisor is greater than 1024, the result may not fit
+in a 24-bit word.
+To fix this, the summed values are divided by a suitable power of 2. <br>
+If _N_ &le; 1024, the effective downsample gain is equal to _N_. <br>
+If _N_ &gt; 1024, the effective downsample gain is equal to _N_ / 2<sup>_k_</sup>, where _k_ = ceil(log<sub>2</sub>(_N_ / 1024)).
+
+### Triggering
+
+When a trigger occurs, the system collects a record consisting of a
+configurable number of (downsampled) samples.
+Samples are collected for all active channels.
+The number of samples collected per trigger must be between 1 and 65536.
+Collected samples are transferred via the network.
+
+There are 3 ways to trigger the system:
+
+- By sending an explicit trigger command.
+- Via an external digital input signal.
+  A record is collected for each trigger pulse in the digital signal.
+- Continuous triggering in auto-trigger mode.
+
+There are 4 digital input signals that can be used for external triggering.
+These signals are connected via pins `DIO0_P` to `DIO3_P` on the Red Pitaya.
+Settings are available to select one of these signals, and
+to trigger on either rising or falling edges of the selected signal.
+
+An optional trigger delay can be specified.
+The delay specifies the number of 8 ns cycles to wait after detecting
+the trigger event and before recording the first ADC sample.
+The external trigger event is subject to a jitter of 1 sample (8 ns).
+
+New trigger events are ignored while the system is still processing a previous trigger.
+
+When auto-trigger mode is active, the system triggers continuously.
+A new trigger occurs as soon as acquisition for the previous trigger has ended, after a dead time controlled by the trigger delay setting.
+In this mode, the sample rate divisor must be at least 2 (or at least 4 in 4-channel mode).
+If the trigger delay is zero, sampling continues accross triggers at a fixed pace controlled by the sample rate divisor.
+This makes it possible to set up continuous streaming sampling.
+
+### Performance limits
+
+Sample rates are limited in a number of ways:
+
+- For acquisition runs up to about 16000 samples, the sample rate
+  is limited by internal data paths in the FPGA.
+  In this case, the sample rate divisor must be at least 1,
+  or at least 2 when operating in 4-channel mode.
+- However, in auto-trigger mode, even for short acquisition runs,
+  the sample rate divisor must be at least 2,
+  or at least 4 when operating in 4-channel mode.
+- For longer acquisition runs, the sample rate is limited by the
+  network transfer rate.
+  In this case, the maximum sample rate is approximately 5 MSa/s,
+  or 2.5 MSa/s when operating in 4-channel mode.
+
+If the configured sample rate is too high, the system will either
+refuse the sample rate setting, or sample data will be lost
+when internal data buffers fill up.
+
+When using external triggering, the maximum trigger rate depends
+on the time it takes to complete data collection for a trigger.
+The system is ready to accept a new trigger as soon as data collection
+for the previous trigger ends.
+At high sample rates, the maximum trigger rate is eventually also limited
+by the data transfer rate via the network.
+
+### Calibration
+
+The analog inputs of the Red Pitaya support two different input ranges:
+&plusmn; 1 V and &plusmn; 20 V.
+The range is selected through jumpers on the board.
+Software commands can not change the actual input range.
+
+The firmware does provide commands to specify which input range is used by each channel.
+The firmware also keeps track of calibration coefficients for each channel
+and input range.
+
+Two calibration coefficients, _offset_ and _gain_, establish a linear relation
+between ADC codes and input voltage.
+The conversion formula is as follows:
+
+    adc_code = offset + gain * input_voltage
+
+Input ranges and calibration coefficients can be saved to the SD card of
+the Red Pitaya to be preserved across power cycles.
+
+
+## Timetagger operation
+
+The timetagger subsystem detects changes on digital input signals
+and assigns timestamps to such events.
+The stream of timetagged events is transferred via the network.
+
+The timestamp resolution is the same as the ADC sample rate, 125 MHz.
+Timestamps are expressed in units of 8 ns cycles.
+
+### Digital input signals
+
+The timetagger has 4 digital input channels.
+These signals are connected via pins `DIO0_P` to `DIO3_P` on the Red Pitaya.
+
+Each input channel produces two types of events: rising edge events and falling edge events.
+Each event type of each channel can be separately enabled or disabled for timetagging.
+
+
+## Firmware installation
+
+- Use a micro SD card, at least 1 GB.
+- Get the PuzzleFW firmware image `puzzlefw_sdcard.img`
+- Put the SD card in a Linux PC.
+- Find out the device name of the SD card `/dev/sdX` where `X` is replaced by another letter.
+  Be **very careful** to get the device name right.
+  Other storage devices in the PC have similar names.
+  Writing the image will destroy all other data on the target device.
+  If you accidentally write the image to the main drive of your PC, you will have a very bad day.
+- Make sure that the SD card is not mounted by some automatic device management subsystem in your PC.
+- Run the following command as root: <br>
+  `dd if=puzzlefw_sdcard.img of=/dev/sdX bs=1M`
+  <br>
+  This command may take a few minutes to complete.
+- Run `sync` and `eject /dev/sdX` before removing the SD card from the PC.
+
+The SD card image can also be written on a PC with a different operating system than Linux.
+The steps to do this are described in the official Red Pitaya documentation.
+
+
+## Console access
+
+The USB console port on the Red Pitaya can be used to login on
+the Linux system running on the board.
+This is mostly useful for debugging.
+
+To access the console, use a terminal program such as `minicom`
+to open the USB serial port of the Red Pitaya.
+Set the baud rate to 115200 bps, character format to `8N1`.
+
+Press Enter to get a login prompt on the console.
+Use login `root` with password `root`.
+
+
+## Network access
+
+Remote access to the acquisition system is supported via TCP connections.
+Three TCP server ports are used:
+
+- port 5001 is used to transfer analog sample data;
+- port 5002 is used to transfer timetagger data;
+- port 5025 is used for commands.
+
+### Default IP address settings
+
+By default, the system attempts to obtain an IPv4 address via DHCP.
+If the DHCP request fails, the system chooses a link-local address in
+the range 169.254.x.x.
+
+As an alternative to DHCP, a static IPv4 address can be configured via remote control commands.
+
+The system has a unique host name `rp-xxxxxx.local`,
+where the x characters are replaced by the last 6 digits of
+the MAC address.
+This is the same host name as used by the official Red Pitaya software.
+
+### SSH access
+
+It is possible to run an SSH server on the Red Pitaya.
+This can be used to remotely log in on the Linux system.
+
+To login via SSH, use username `root` with password `root`.
+
+For security reasons, the SSH server is disabled by default.
+An SSH server with an easy-to-guess password should never be connected to an untrusted network.
+
+If you want to use the SSH server, you have to enable it explicitly.
+To enable the SSH server, login on the USB console as described above.
+Then run the following command: `puzzle-sshcfg enable` .
+Finally, run `reboot` to reboot the Red Pitaya.
+From this point onward, the SSH server will be started automatically during boot.
+
+
+## Data stream protocol
+
+Clients may connect to TCP port 5001 to receive analog sample data,
+and to TCP port 5002 to receive timetagger data.
+
+At most one client can be connected to each of these ports at any time.
+If a new client connects while another connection is still active,
+the server closes the old connection and uses the new connection instead.
+
+Data flows through these TCP connections in one direction:
+from the server to the client.
+The client must not send anything back to the server.
+
+Data are transferred as a sequence of 64-bit binary messages.
+Each message is sent as 8 bytes with the least significant byte first.a
+The message streams correspond to the output data format of the
+analog acquisition chain and the timetagger as described in the
+[FPGA firmware documentation](fpga_firmware.md#).
+
+
+## Remote control protocol
+
+Clients may connect to TCP port 5025 to send commands.
+Multiple clients may be simultaneously connected to this port.
+In that case, it is the responsibility of the clients to make sure
+that they do not interfere with eachother.
+
+The remote control protocol is based on ASCII strings.
+The protocol is vaguely similar to SCPI, but it is not compatible with SCPI.
+
+Every interaction is initiated by the client sending a command,
+and completed by the server sending a response.
+Each command and each response consists of an ASCII string terminated by linefeed (ASCII 10).
+Commands are case-insensitive.
+
+The server ignores empty lines and lines that contain only white space characters.
+In all other cases, the server sends one response for every command received, even if the command is not recognized or not supported.
+The server only sends data in response to a command; it never sends data spontaneously.
+
+A _query_ is a command that ends with a `?` character.
+The server responds to a query either by sending the requested data,
+or by sending an error message.
+An error message starts with the string `ERROR`, followed by
+a space character, followed by a short description of the error.
+
+The server responds to a non-query command either by sending the string `OK`
+to indicate that the command was completed successfully,
+or by sending an error message.
+
+Some commands require one or more _parameters_.
+In the command string, the command and parameters are separated from eachother by space characters.
+
+The response to some queries may consist of multiple data elements.
+In the response string, such data elements are separated by space characters.
+
+### Example
+
+| Client                   | Server        |
+|--------------------------|---------------|
+| `AIN:SRATE?`             |               |
+|                          | `1000000.000` |
+| `AIN:SRATE:DIVISOR 1000` |               |
+|                          | `OK`          |
+| `AIN:SRATE?`             |               |
+|                          | `125000.000`  |
+| `AIN:NSAMPLES 0`         |               |
+|                          | `ERROR Invalid argument` |
+| `Hello`                  |               |
+|                          | `ERROR Unknown command` |
+
+### List of commands and queries
+
+| Command                   | Description |
+|---------------------------|-------------|
+| `*IDN?`                   | Instrument identification. |
+| `RESET`                   | Restore default settings. |
+| `TIMESTAMP?`              | Timestamp counter. |
+| `AIN:CHANNELS:COUNT?`     | Number of input channels. |
+| `AIN:CHANNELS:ACTIVE`     | Number of active input channels. |
+| `AIN:CHn:RANGE`           | Analog input range. |
+| `AIN:CHn:OFFSET`          | Offset calibration. |
+| `AIN:CHn:GAIN`            | Gain calibration. |
+| `AIN:CAL:SAVE`            | Save calibration. |
+| `AIN:CHn:SAMPLE[:RAW]?`   | Read ADC sample. |
+| `AIN:CHn:MINMAX[:RAW]?`   | Read ADC range monitor. |
+| `AIN:MINMAX:CLEAR`        | Reset ADC range monitor. |
+| `AIN:SRATE`               | Sample rate. |
+| `AIN:SRATE:DIVISOR`       | Downsample factor. |
+| `AIN:SRATE:MODE`          | Downsample mode. |
+| `AIN:SRATE:GAIN?`         | Downsample gain. |
+| `AIN:NSAMPLES`            | Number of samples per trigger. |
+| `AIN:TRIGGER`             | Force a trigger event. |
+| `AIN:TRIGGER:MODE`        | Select trigger mode. |
+| `AIN:TRIGGER:DELAY`       | Trigger delay. |
+| `AIN:TRIGGER:STATUS?`     | Trigger status. |
+| `AIN:TRIGGER:EXT:CHANNEL` | External trigger channel. |
+| `AIN:TRIGGER:EXT:EDGE`    | External trigger edge. |
+| `AIN:ACQUIRE:ENABLE`      | Enable analog acquisition. |
+| `TT:SAMPLE?`              | Digital input state. |
+| `TT:EVENT:MASK`           | Timetagger event mask. |
+| `TT:MARK`                 | Emit timetagger marker. |
+| `TEMP:FPGA?`              | FPGA temperature. |
+| `IPCFG[:SAVED]`           | IP address configuration. |
+| `HALT`                    | Shut down system. |
+| `REBOOT`                  | Reboot system. |
+
+### `*IDN?`
+
+Query: `*IDN?` <br>
+Response: string with 4 comma-separated fields.
+
+This query returns the instrument identification string.
+The response consists of 4 comma-separated fields:
+`manufacturer,model,serialnr,version`.
+
+### `RESET`
+
+Command: `RESET`
+
+This command restores most non-persistent settings to power-on defaults.
+It resets all settings, except for the following:
+
+- saved calibration;
+- active network configuration;
+- saved network configuration.
+
+The active calibration is restored to match the saved calibration.
+Other settings are restored to fixed power-on defaults.
+
+Any ongoing analog acquisition is stopped.
+
+### `TIMESTAMP?`
+
+Query: `TIMESTAMP?` <br>
+Response: decimal integer, representing the current timestamp in units of 8 ns.
+
+### `AIN:CHANNELS:COUNT?`
+
+Query: `AIN:CHANNELS:COUNT?` <br>
+Response: number of supported analog input channels.
+
+The response is `2` for a standard Red Pitaya, or `4` for a 4-input Red Pitaya.
+
+### `AIN:CHANNELS:ACTIVE`
+
+Command: `AIN:CHANNELS:ACTIVE n` <br>
+Parameter _n_: number of active channels, either `2` or `4`.
+
+This command is only supported on a 4-input Red Pitaya.
+When 2 channels are active, only analog input channels 1 and 2 are included in analog acquisition data.
+
+Query: `AIN:CHANNELS:ACTIVE?` <br>
+Response: number of active channels, either `2` or `4`.
+
+### `AIN:CHn:RANGE`
+
+Command: `AIN:CHn:RANGE range` <br>
+Field _n_: channel number, in range 1 to 4. <br>
+Parameter _range_: input range, either `LO` or `HI`.
+
+This command specifies which set of calibration coefficients should be used to interpret ADC samples.
+Note that this command does not change the actual input range of the Red Pitaya.
+The input range can only be changed by manually placing a jumper on the board.
+
+Query: `AIN:CHn:RANGE?` <br>
+Response: currently configured input range, either `LO` or `HI`.
+
+### `AIN:CHn:OFFSET[:LO|HI]`
+
+Command: `AIN:CHn:OFFSET offs` <br>
+Field _n_: channel number, in range 1 to 4. <br>
+Parameter _offs_: floating point number specifying the offset calibration.
+
+The offset calibration specifies the raw ADC code corresponding to analog input level 0 Volt.
+The expected value is in the middle of the ADC code range, i.e. approximately 8192.
+The plain variant of the command configures the offset calibration for the active input range of the channel.
+
+Command: `AIN:CHn:OFFSET:LO offs` <br>
+Command: `AIN:CHn:OFFSET:HI offs` <br>
+These variants of the command configure the offset calibration for a specific input range.
+
+Query: `AIN:CHn:OFFSET?` <br>
+Query: `AIN:CHn:OFFSET:LO?` <br>
+Query: `AIN:CHn:OFFSET:HI?` <br>
+Response: floating point number indicating the offset calibration for the active input range or the specified input range.
+
+### `AIN:CHn:GAIN[:LO|HI]`
+
+Command: `AIN:CHn:GAIN gain` <br>
+Field _n_: channel number, in range 1 to 4. <br>
+Parameter _gain_: floating point number specifying the gain calibration.
+
+The gain calibration specifies the difference in raw ADC code corresponding to a 1 Volt difference in analog input level.
+The expected value is negative, because the Red Pitaya uses an inverting input amplifier.
+The plain variant of the command configures the gain calibration for the active input range of the channel.
+
+Command: `AIN:CHn:GAIN:LO offs` <br>
+Command: `AIN:CHn:GAIN:HI offs` <br>
+These variants of the command configure the gain calibration for a specific input range.
+
+Query: `AIN:CHn:GAIN?` <br>
+Query: `AIN:CHn:GAIN:LO?` <br>
+Query: `AIN:CHn:GAIN:HI?` <br>
+Response: floating point number indicating the gain calibration for the active input range or the specified input range.
+
+### `AIN:CAL:SAVE`
+
+Command: `AIN:CAL:SAVE`
+
+This command saves the active calibration settings to the SD card, to be used as power-on defaults.
+The following settings are saved for each analog input channel: its input range, offset calibration for low and high range, and gain calibration for low and high range.
+
+### `AIN:CHn:SAMPLE[:RAW]?`
+
+Query: `AIN:CHn:SAMPLE?` <br>
+Field _n_: channel number, in range 1 to 4. <br>
+Response: floating point number representing the most recent ADC sample for the specified input channel in Volt.
+
+Query: `AIN:CHn:SAMPLE:RAW?` <br>
+Response: decimal integer representing the raw ADC code of the most recent sample for the specified input channel.
+
+Sample rate settings are not applicable to this command.
+The ADC always samples at 125 MSa/s.
+This command returns the most recent single sample, without downsampling or averaging.
+
+### `AIN:CHn:MINMAX[:RAW]?`
+
+Query: `AIN:CHn:MINMAX?` <br>
+Field _n_: channel number, in range 1 to 4. <br>
+Response: two floating point numbers separated by a space character, representing the minimum and maximum input level in Volt.
+
+Query: `AIN:CHn:MINMAX:RAW?` <br>
+Response: two decimal integers separated by a space character, representing the minimum and maximum raw ADC code.
+
+The returned values are the minimum and maximum sample values that occurred since the last reset of the range monitor.
+
+### `AIN:MINMAX:CLEAR`
+
+Command: `AIN:MINMAX:CLEAR`
+
+This command resets the input range monitors of all analog input channels.
+
+### `AIN:SRATE`
+
+Command: `AIN:SRATE rate` <br>
+Parameter _rate_: floating point number specifying the sample rate in samples per second.
+
+This command configures the effective sample rate of the acquisition chain.
+Valid sample rates are in range 500 to 125e6 samples per second.
+The specified sample rate will be rounded to the nearest supported rate.
+
+Query: `AIN:SRATE?` <br>
+Response: floating point number representing the sample rate in samples per second.
+
+### `AIN:SRATE:DIVISOR`
+
+Command: `AIN:SRATE:DIVISOR divisor` <br>
+Parameter _divisor_: decimal integer specifying the downsample factor.
+
+This command configures the downsample factor of the acquisition chain.
+Valid downsample factors are in range 1 to 250000.
+
+Query: `AIN:SRATE:DIVISOR?` <br>
+Response: decimal integer representing the downsample factor.
+
+**Note:** Commands `AIN:SRATE` and `AIN:SRATE:DIVISOR` are different methods to control the same internal setting.
+
+**Note:** When auto-trigger mode is selected, the downsample factor must be at least 2, or 4 if 4 channels are active.
+In other trigger modes, the downsample factor must be at least 1, or 2 if 4 channels are active.
+
+### `AIN:SRATE:MODE`
+
+Command: `AIN:SRATE:MODE mode` <br>
+Parameter _mode_: downsample mode, either `DECIMATE` or `AVERAGE`.
+
+This command selects downsampling by means of decimation or averaging.
+Downsampling works by collecting groups of consecutive raw ADC samples and translating each group into a single downsampled value.
+The number of raw samples per group is determined by the downsample factor (see `AIN:SRATE:DIVISOR`).
+In mode `DECIMATE`, the first sample of a group is used as downsampled value; the other samples in the group are discarded.
+In mode `AVERAGE`, the sum of all samples in a group is used as downsampled value.
+
+Query: `AIN:SRATE:MODE?` <br>
+Response: either `DECIMATE` or `AVERAGE`.
+
+### `AIN:SRATE:GAIN?`
+
+Query: `AIN:SRATE:GAIN?` <br>
+Response: floating point number representing the effective gain factor due to downsampling.
+
+The value returned by this query depends on the downsample factor and the downsample mode.
+
+In downsample mode `DECIMATE`, this query always returns 1.0.
+In downsample mode `AVERAGE`, this query returns a number between 1 and 1024.
+
+### `AIN:NSAMPLES`
+
+Command: `AIN:NSAMPLES n` <br>
+Parameter _n_: decimal integer specifying the number of samples per channel per trigger.
+
+This command configures the number of (downsampled) samples to collect for each trigger.
+Valid values are from 1 to 65536.
+
+Query: `AIN:NSAMPLES?` <br>
+Response: decimal integer representing the number of samples per trigger.
+
+### `AIN:TRIGGER`
+
+Command: `AIN:TRIGGER`
+
+This command forces a trigger to occur, regardless of the configured trigger mode.
+
+Note that even a forced trigger may be ignored if the acquisition chain is still processing a previous trigger.
+
+### `AIN:TRIGGER:MODE`
+
+Command: `AIN:TRIGGER:MODE mode` <br>
+Parameter _mode_: trigger mode, either `NONE` or `AUTO` or `EXTERNAL` or `EXTERNAL_ONCE`.
+
+**Note:** When trigger mode `EXTERNAL_ONCE` is selected, the trigger mode automatically changes to `NONE` as soon as a trigger occurs.
+
+Query: `AIN:TRIGGER:MODE?` <br>
+Response: active trigger mode.
+
+### `AIN:TRIGGER:DELAY`
+
+Command: `AIN:TRIGGER:DELAY n` <br>
+Parameter _n_: decimal integer specifying trigger delay as a number of 8 ns cycles.
+
+This configures a delay between trigger detection and the start of sample collection.
+Valid values are from 0 to 65535.
+
+Query: `AIN:TRIGGER:DELAY?` <br>
+Response: decimal integer representing the trigger delay as a number of 8 ns cycles.
+
+### `AIN:TRIGGER:STATUS?`
+
+Query: `AIN:TRIGGER:STATUS?` <br>
+Response: trigger status, either `BUSY` or `WAITING`.
+
+This query returns `BUSY` when the acquisition chain is processing a trigger, or `WAITING` if the acquisition chain is waiting for a trigger.
+
+### `AIN:TRIGGER:EXT:CHANNEL`
+
+Command: `AIN:TRIGGER:EXT:CHANNEL n` <br>
+Parameter _n_: decimal integer specifying a digital input channel, in range 0 to 3.
+
+This command selects the digital input channel to use as external trigger.
+
+Query: `AIN:TRIGGER:EXT:CHANNEL?` <br>
+Response: decimal integer specifying the selected digital input channel.
+
+### `AIN:TRIGGER:EXT:EDGE`
+
+Command: `AIN:TRIGGER:EXT:EDGE edge` <br>
+Parameter _edge_: trigger edge, either `RISING` or `FALLING`.
+
+This command selects rising or falling edges in the external trigger signal.
+
+Query: `AIN:TRIGGER:EXT:EDGE?` <br>
+Response: either `RISING` or `FALLING`.
+
+### `AIN:ACQUIRE:ENABLE`
+
+Command: `AIN:ACQUIRE:ENABLE en` <br>
+Parameter _en_: either `0` or `1`.
+
+This command enables or disables analog acquisition.
+When enabled, analog samples are acquired according to the configured trigger mode.
+When disabled, all triggers are ignored and any ongoing analog acquisition stops immediately.
+
+Query: `AIN:ACQUIRE:ENABLE?` <br>
+Response: either `0` or `1`.
+
+### `TT:SAMPLE?`
+
+Query: `TT:SAMPLE?` <br>
+Response: array of 4 digits `0` or `1`, separated by space characters.
+
+This query returns the input state of all digital input channels.
+
+### `TT:EVENT:MASK`
+
+Command: `TT:EVENT:MASK mask` <br>
+Parameter _mask_: decimal integer specifying a bit mask of enabled events.
+
+This command configures the set of enabled timetagger events.
+The integer value of _mask_ represents an 8-bit mask.
+Each bit position denotes an event type, as follows:
+
+| Bit index | Value | Description |
+|-----------|-------|-------------|
+| 0         | 1     | Rising edge on digital input 0. |
+| 1         | 2     | Falling edge on digital input 0. |
+| 2         | 4     | Rising edge on digital input 1. |
+| 3         | 8     | Falling edge on digital input 1. |
+| 4         | 16    | Rising edge on digital input 2. |
+| 5         | 32    | Falling edge on digital input 2. |
+| 6         | 64    | Rising edge on digital input 3. |
+| 7         | 128   | Falling edge on digital input 3. |
+
+Query: `TT:EVENT:MASK?` <br>
+Response: decimal integer representing the event mask.
+
+### `TT:MARK`
+
+Command: `TT:MARK`
+
+This command emits a marker record in the timetagger event stream.
+
+### `TEMP:FPGA?`
+
+Query: `TEMP:FPGA?` <br>
+Response: floating point number representing the temperature in Celsius.
+
+The temperature is measured by the internal temperature sensor of the Zynq FPGA.
+
+### `IPCFG[:SAVED]`
+
+Command: `IPCFG DHCP` <br>
+Command: `IPCFG STATIC ipaddr netmask gateway` <br>
+Parameter _ipaddr_: IPv4 address in dotted-quad notation. <br>
+Parameter _netmask_: netmask in dotted-quad notation. <br>
+Parameter _gateway_: optional gateway address in dotted-quad notation.
+
+This command configures the IP address of the system.
+It expects between 1 and 4 parameters, depending on the specific address configuration.
+
+If address mode `DHCP` is selected, the command expects no further parameters.
+In this mode, the system attempts to get an IPv4 address from a DHCP server on the local network.
+
+If address mode `STATIC` is selected, the command expects 2 or 3 additional parameters to specify the address, netmask and optional gateway.
+IP addresses are specified in _dotted-quad_ notation: 4 decimal integers separated by period characters.
+The parameter _gateway_ may be omitted or specified as `0.0.0.0` to indicate that no gateway should be used.
+
+The command `IPCFG` takes effect immediately.
+This command does not send an `OK` response.
+Instead, all TCP connections are closed while the system prepares to change its IP address.
+Changing the IP address typically takes a few seconds.
+When the new address is active, the client may re-connect to the new IP address.
+
+**Note:** Configuring an invalid IP address may make the system unreachable.
+In that case, the saved IP address configuration can be restored by power-cycling the system.
+
+Command: `IPCFG:SAVED DHCP` <br>
+Command: `IPCFG:SAVED STATIC ipaddr netmask gateway`
+
+This variant of the command configures the saved IP address configuration.
+It uses the same set of parameters as `IPCFG`.
+This command has no effect on the active IP address.
+When the command completes, it sends an `OK` response and the system continues to function normally.
+The saved address configuration takes effect on the next reboot of the system.
+
+Query: `IPCFG?` <br>
+Query: `IPCFG:SAVED?` <br>
+Response: active or saved IP address configuration.
+
+### `HALT`
+
+Command: `HALT`
+
+This command iniates a shutdown of the system.
+It does not send an `OK` response.
+Instead, all TCP connections are closed while the system initiates shutdown.
+
+The halt command causes the system to become unresponsive to further commands.
+To recover from the halt state, the system must be power-cycled.
+
+### `REBOOT`
+
+Command: `REBOOT`
+
+This command initiates a system reboot.
+It does not send an `OK` response.
+Instead, all TCP connections are closed while the system initiates shutdown.
+
+A reboot involves a complete reset of the FPGA and the embedded ARM processor.
+The system then proceeds as if just powered on.
+

sw/.gitignore

@@ -1,3 +1,4 @@
+puzzlefw_sdcard.img
 devicetree/devicetree.dtb
 buildroot_overlay/opt/puzzlefw/bin/puzzlecmd
 buildroot_overlay/opt/puzzlefw/bin/remotectl

sw/22_prepare_sdcard.sh

@@ -29,11 +29,6 @@ cp -a "$BUILDROOT_DIR/output/images/rootfs.cpio.uboot" "$SDCARD_DIR"
 # Wrap U-Boot script in image file
 $MKIMAGE -A arm -T script -d config/uboot_script.txt "$SDCARD_DIR/boot.scr"
 
-# Create SSH host key for embedded system
-if [ ! -f "$SDCARD_DIR/dropbear_ed25519_host_key" ]; then
-    dropbearkey -t ed25519 -f "$SDCARD_DIR/dropbear_ed25519_host_key"
-fi
-
 # Copy FPGA firmware
 cp -a $FIRMWARE_FILES "$SDCARD_DIR"
 

sw/23_sdcard_image.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+set -e
+
+. script_env
+
+# Delete stale output file.
+rm -f "$SDCARD_IMG"
+
+# Create empty SD card image.
+dd if=/dev/zero of="$SDCARD_IMG" bs=1M seek=507 count=1
+
+# Create partition table.
+cat <<END | /sbin/sfdisk "$SDCARD_IMG"
+label: dos
+start=8192, size=512000, type=e
+start=524288, size=512000, type=83
+END
+
+# Create DOS partition.
+/sbin/mkdosfs -F 16 --offset 8192 ${SDCARD_IMG} 256000
+
+# Copy files to SD card.
+mcopy -i ${SDCARD_IMG}@@4M ${SDCARD_DIR}/* ::
+
+# Create empty ext4 partition for configuration.
+/sbin/mke2fs -t ext4 -b 4096 -E offset=$((524288 * 512)) ${SDCARD_IMG} 256000k
+

sw/buildroot_overlay/etc/default/dropbear

@@ -0,0 +1,13 @@
+# Read config file to see if SSH server must be started.
+
+start_ssh=0
+
+if [ -f /var/lib/puzzlefw/cfg/start_ssh.conf ]; then
+    . /var/lib/puzzlefw/cfg/start_ssh.conf
+fi
+
+if [ "${start_ssh}" -ne 1 ]; then
+    echo "SSH server disabled in configuration, not starting dropbear."
+    exit 1
+fi
+

sw/buildroot_overlay/etc/init.d/S03read_config.sh

@@ -5,11 +5,32 @@
 
 . /opt/puzzlefw/lib/functions.sh
 
+# Copy SSH host key from configuration partition.
+copy_ssh_host_key() {
+
+    # If host key exists, do nothing.
+    [ -f /etc/dropbear/dropbear_ed25519_host_key ] && return
+
+    # If /etc/dropbear is a symlink, delete it.
+    [ -L /etc/dropbear ] && rm /etc/dropbear
+
+    # Create directory /etc/dropbear if it does not exist.
+    mkdir -p /etc/dropbear
+
+    # Try to copy SSH host key from configuration files.
+    if ! cp -p ${CONFIG_DIR}/dropbear_ed25519_host_key /etc/dropbear ; then
+        echo "WARNING: Failed to load SSH host key from SD card" >&2
+    fi
+
+    chmod 0600 /etc/dropbear/dropbear_ed25519_host_key || true
+}
+
 case "$1" in
   start)
     echo "Reading configuration files from SD card ..."
     lock_config || exit 1
     read_config || exit 1
+    copy_ssh_host_key
     ;;
   stop|restart|reload)
     true

sw/buildroot_overlay/etc/init.d/S10prepare_dropbear.sh

@@ -1,44 +0,0 @@
-#!/bin/sh
-#
-# Load SSH host key from SD card.
-#
-
-start() {
-
-    # If host key exists, do nothing.
-    [ -f /etc/dropbear/dropbear_ed25519_host_key ] && return
-
-    # If /etc/dropbear is a symlink, delete it.
-    [ -L /etc/dropbear ] && rm /etc/dropbear
-
-    # Create directory /etc/dropbear if it does not exist.
-    mkdir -p /etc/dropbear
-
-    # Try to copy SSH host key from SD card.
-    mkdir -p /mnt/tmp_sdcard
-    mount -t vfat -o fmask=0177 -r /dev/mmcblk0p1 /mnt/tmp_sdcard
-
-    if ! cp -p /mnt/tmp_sdcard/dropbear_ed25519_host_key /etc/dropbear ; then
-        echo "WARNING: Failed to load SSH host key from SD card" >&2
-        umount /mnt/tmp_sdcard
-        rmdir /mnt/tmp_sdcard
-        exit 1
-    fi
-
-    umount /mnt/tmp_sdcard
-    rmdir /mnt/tmp_sdcard
-
-    chmod 0600 /etc/dropbear/dropbear_ed25519_host_key
-}
-
-case "$1" in
-  start)
-    start
-    ;;
-  stop|restart|reload)
-    ;;
-  *)
-    echo "Usage: $0 start"
-    exit 1
-esac
-

sw/buildroot_overlay/opt/puzzlefw/bin/puzzle-sshcfg

@@ -0,0 +1,105 @@
+#!/bin/sh
+#
+# Enable or disable SSH server.
+#
+
+. /opt/puzzlefw/lib/functions.sh
+
+# Show current configuration.
+show() {
+
+    start_ssh=0
+    if [ -f ${CONFIG_DIR}/start_ssh.conf ]; then
+        . ${CONFIG_DIR}/start_ssh.conf
+    fi
+
+    if [ "${start_ssh}" -eq 1 ]; then
+        echo "Current setting: start SSH on boot"
+    else
+        echo "Current setting: do not start SSH on boot"
+    fi
+
+    if [ -f ${CONFIG_DIR}/dropbear_ed25519_host_key ]; then
+        dropbearkey -y -f ${CONFIG_DIR}/dropbear_ed25519_host_key
+    fi
+}
+
+# Generate persistent SSH host key, if necessary.
+gen_key() {
+
+    # Do nothing if host key already exists in config partition.
+    [ -f ${CONFIG_DIR}/dropbear_ed25519_host_key ] && return
+
+    # If no host key exists, generate it.
+    if [ ! -f /etc/dropbear/dropbear_ed25519_host_key ]; then
+
+	echo "Generating SSH host key ..."
+
+        # If /etc/dropbear is a symlink, delete it.
+        [ -L /etc/dropbear ] && rm /etc/dropbear
+
+        # Create directory /etc/dropbear if it does not exist.
+        mkdir -p /etc/dropbear
+
+        # Generate host key.
+        dropbearkey -t ed25519 -f /etc/dropbear/dropbear_ed25519_host_key
+    fi
+
+    echo "Writing SSH host key to config partition ..."
+
+    cp -a /etc/dropbear/dropbear_ed25519_host_key ${CONFIG_DIR}/dropbear_ed25519_host_key.new
+    sync_config dropbear_ed25519_host_key || exit 1
+}
+
+# Enable starting SSH server during boot.
+enable() {
+
+    lock_config || exit 1
+
+    gen_key
+
+    echo "Enabling SSH server start on boot ..."
+
+    echo "start_ssh=1" > ${CONFIG_DIR}/start_ssh.conf.new
+    sync_config start_ssh.conf || exit 1
+}
+
+# Disable starting SSH server during boot.
+disable() {
+
+    lock_config || exit 1
+
+    echo "Disabling SSH server start on boot ..."
+
+    echo "start_ssh=0" > ${CONFIG_DIR}/start_ssh.conf.new
+    sync_config start_ssh.conf || exit 1
+}
+
+case "$1" in
+  show)
+    show
+    ;;
+  enable)
+    enable
+    ;;
+  disable)
+    disable
+    ;;
+  *)
+    script="${0##*/}"
+    cat <<EOF
+Usage: $script {enable|disable}"
+
+  $script show
+    Show current configuration.
+
+  $script enable
+    Enable starting SSH server during boot.
+
+  $script disable
+    Disable starting SSH server during boot.
+
+EOF
+    exit 1
+esac
+

sw/buildroot_overlay/opt/puzzlefw/lib/functions.sh

@@ -32,7 +32,8 @@ read_config() {
     mount -t ext4 -r -o noatime,data=journal /dev/${CONFIG_PARTITION} $CONFIG_MOUNTPOINT || return 1
 
     # Copy config files to RAM filesystem.
-    cp -a ${CONFIG_MOUNTPOINT}/*.conf $CONFIG_DIR
+    cp -a ${CONFIG_MOUNTPOINT}/*.conf $CONFIG_DIR || true
+    cp -a ${CONFIG_MOUNTPOINT}/dropbear_* $CONFIG_DIR || true
 
     umount $CONFIG_MOUNTPOINT
 }

sw/script_env

@@ -16,6 +16,7 @@ LINUX_DIR="linux-xlnx"
 
 BOOTIMG_DIR="boot_img"
 SDCARD_DIR="sdcard_files"
+SDCARD_IMG="puzzlefw_sdcard.img"
 
 XSA_FILE="../fpga/redpitaya_puzzlefw.xsa"
 FIRMWARE_FILES="../fpga/puzzlefw_top.bit.bin ../fpga/puzzlefw_top_4ch.bit.bin"

sw/src/userspace/remotectl.cpp

@@ -1118,7 +1118,7 @@ private:
             min_divisor *= 2;
         }
         if (ch4) {
-            min_divisor += 2;
+            min_divisor *= 2;
         }
         return min_divisor;
     }

sw/src/userspace/version.hpp

@@ -1,2 +1,2 @@
 #define PUZZLEFW_SW_MAJOR 0
-#define PUZZLEFW_SW_MINOR 4
+#define PUZZLEFW_SW_MINOR 5