lidarTDC

System requirements

• Time-to-digital converter (TDC) for atmospheric Lidar applications
• Temporal resolution <= 10 ns
• Integration time >= 2 ms
• Multiple input ports (N >= 5)
• Trigger input
• 8 bit temporal timestamp prefix
• External ref clk (10MHz)

System architecture

• Central Control System. Central control, orchestration and analysis unit. Configures peripheral devices via ethernet.
• Cora-Z7-10. Digilent low cost development board (see here) featuring a Xilinx Zynq 7010 SoC FPGA, 1Gbps Ethernet PHY, RAM memory, USB hub, 45 Arduino compatible IOs (3.3V CMOS)...
• Zynq7010 FPGA. System on a chip. Contains a 32bit-ARM processing system (PS) and programable logic (PL).
• RAM. 512MB DDR3 memory. Accessible to both PS and PL (via DMA).
• Python Server. Devoted to the configuration/operation of the PL. It is has direct access to the data stored in the RAM memory. Communication with the Central Control System is performed over the 1Gbps etherent PHY.
• FSM. Finite state machine implementing the TDC logic. Minimum pulse width: 5ns (use IDDR to sample at both edges of 100 MHz clk and OR gate the outputs Q1 and Q2). Temporal resolution: 10ns (rising edge of 100 MHz clk). Minimum pulse separation: 20 ns. 64bit time stamping:
  • 23-00 : counter (max integration time: 167 ms).
  • 31-24 : external timestamp.
  • 63-32 : mask (used to mark the inputs on which a rising edge has been detected). Max number of detectors: 32.
• PLL. Phase lock loop.
• DMA. Direct memory access. Streams 64bit timestamps from FSM to RAM.
• I2C master with 100kHz SCL. This logic is only used in the C++ Backend branch of this repository.

Initial configuration

1. Download the SD card image Pynq-Cora-Z7-10-2.5.img.

2. Write SD card image. For instruction see here.

3. Configure jumper J2 of the Cora-Z7 board for microSD card boot. Further information is available in the Cora-Z7 reference manual.

4. Power up the device and connect it to your ethernet router/switch.

5. Find the automatically assigned IP address of the device. This is most easily achieved by entering the configuration panel of your router or by using a network scanning tool.

6. SSH into your Cora-Z7-10 (usr: xilinx pwd: xilinx):

ssh xilinx@<IP address>

7. Change the etherent settings to use a static IP address.

sudo vi /etc/network/interfaces.d/eth0

Change the eth0 interface configuration to

auto eth0
iface eth0 inet dhcp 
          
auto eth0:1
iface eth0:1 inet static
address <static IP address>
netmask <netmask>

8. Power off/on the device.

9. Create a network drive linked to the Samba file server running on your Pynq machine:

File server property	Value
url	//<static IP address>/xilinx
usr	xilinx
pwd	xilinx

i) pulseAcq

10. Using the file server, navigate to /xilinx/pynq/overlays/.

11. Create a folder called /xilinx/pynq/overlays/pulseAcq and copy in it the pulseAcq.bit, pulseAcq.tcl and pulseAcq.hwh files.

12. Using the file server, navigate to /xilinx/jupyter_notebooks.

13. Create a folder called /xilinx/jupyter_notebooks/pulseAcq and copy in it the pulseAcq.ipynb and pulseAcqServer.py files.

ii) pulseGen

10. Using the file server, navigate to /xilinx/pynq/overlays/.

11. Create a folder called pynq/overlays/pulseGen and copy in it the pulseGen.bit, pulseGen.tcl and pulseGen.hwh files.

12. Using the file server, navigate to /xilinx/jupyter_notebooks.

13. Create a folder called /xilinx/jupyter_notebooks/pulseGen and copy in it the pulseGen.ipynb, pulseGenServer.py and pulseGenCachedServer.py files.

Port assignements

i) pulseAcq

Pin	Direction	IO Standard	Description
0	In	LVCMOS 3.3V	Pulse channel 0
1	In	LVCMOS 3.3V	Pulse channel 1
2	In	LVCMOS 3.3V	Pulse channel 2
3	In	LVCMOS 3.3V	Pulse channel 3
4	In	LVCMOS 3.3V	Pulse channel 4
5	In	LVCMOS 3.3V	Pulse channel 5
6	In	LVCMOS 3.3V	Pulse channel 6
7	In	LVCMOS 3.3V	Pulse channel 7
8	In	LVCMOS 3.3V	Ref clk (10 MHz)
9	In	LVCMOS 3.3V	Trig (rising edge)
26	In	LVCMOS 3.3V	Timestamp bit 0
27	In	LVCMOS 3.3V	Timestamp bit 1
28	In	LVCMOS 3.3V	Timestamp bit 2
29	In	LVCMOS 3.3V	Timestamp bit 3
30	In	LVCMOS 3.3V	Timestamp bit 4
31	In	LVCMOS 3.3V	Timestamp bit 5
32	In	LVCMOS 3.3V	Timestamp bit 6
33	In	LVCMOS 3.3V	Timestamp bit 7
SCL	In/Out	LVCMOS 3.3V	I2C clk
SDA	In/Out	LVCMOS 3.3V	I2C data

ii) pulseGen

Pin	Direction	IO Standard	Description
0	Out	LVCMOS 3.3V	Pulse channel 0
1	Out	LVCMOS 3.3V	Pulse channel 1
2	Out	LVCMOS 3.3V	Pulse channel 2
3	Out	LVCMOS 3.3V	Pulse channel 3
4	Out	LVCMOS 3.3V	Pulse channel 4
5	Out	LVCMOS 3.3V	Pulse channel 5
6	Out	LVCMOS 3.3V	Pulse channel 6
7	Out	LVCMOS 3.3V	Pulse channel 7
8	Out	LVCMOS 3.3V	Ref clk (10 MHz)
9	Out	LVCMOS 3.3V	Trig (rising edge)
26	Out	LVCMOS 3.3V	Timestamp bit 0
27	Out	LVCMOS 3.3V	Timestamp bit 1
28	Out	LVCMOS 3.3V	Timestamp bit 2
29	Out	LVCMOS 3.3V	Timestamp bit 3
30	Out	LVCMOS 3.3V	Timestamp bit 4
31	Out	LVCMOS 3.3V	Timestamp bit 5
32	Out	LVCMOS 3.3V	Timestamp bit 6
33	Out	LVCMOS 3.3V	Timestamp bit 7

Running the Jupyter notebooks

1. Connect to the Jupyter notebook server by introducing the static IP address of your Cora-Z7 board into your web browser (pwd: xilinx).

i) pulseAcq

2. Within your Jupyter notebook server, navigate to the pulseAcq directory and open the pulseAcq.ipynb. This interactive notebook is a basic example of the pulseAcq operation.

ii) pulseGen

2. Within your Jupyter notebook server, navigate to the pulseGen directory and open the pulseGen.ipynb. This interactive notebook is a basic example of the pulseGen operation.

Running the TCP servers

1. SSH into your Cora-Z7-10 (usr: xilinx pwd: xilinx):

ssh xilinx@<static IP address>

i) pulseAcq

2. Navigate to the jupyter_notebooks/pulseAcq folder.

cd jupyter_notebooks/pulseAcq

3. Execute the pulseAcqServer.py script

sudo python3 pulseAcqServer.py <static IP address> <TCP port>

ii) pulseGen

2. Navigate to the jupyter_notebooks/pulseGen folder.

cd jupyter_notebooks/pulseGen

3. Execute the pulseGenCachedServer.py script

sudo python3 pulseGenCachedServer.py <static IP address> <TCP port>

Communication between TCP clients and TCP servers

i) pulseAcq

• TCP server: executing pulseAcqServer.py on Cora-Z7-10 board.
• TCP client: any PC with network access to the Cora-Z7-10 board. The TCP client has to establish a new connection to the TCP server, send/receive all data packets and close the connection afterwards.
• Data packets:

Data packet	Direction	Length (bytes)	Description
<ITER>	client -> server	4	Number of trigger events/iterations
<COUNTER_MAX>	client -> server	4	Max integration time for each trigger event (in units of 10ns)
LEN_0	server -> client	4	Trigger 0: length of the following data packet(in units of bytes)
DATA_0	server -> client	LEN_0	Trigger 0: concatenated 64 bit timestamps
LEN_1	server -> client	4	Trigger 1: length of the following data packet (in units of bytes)
DATA_1	server -> client	LEN_1	Trigger 1: concatenated 64 bit timestamps
...	...	...	...
LEN_<ITER - 1>	server -> client	4	Trigger <ITER - 1>: length of the following data packet (in units of bytes)
DATA_<ITER - 1>	server -> client	LEN_<ITER - 1>	Trigger <ITER - 1>: concatenated 64 bit timestamps

NOTE: Pulse acquisition starts after receiving the <ITER> and <COUNTER_MAX> parameters.

ii) pulseGen

• TCP server: executing pulseGenCachedServer.py on Cora-Z7-10 board.
• TCP client: any PC with network access to the Cora-Z7-10 board. The TCP client has to establish a new connection to the TCP server, send/receive all data packets and close the connection afterwards.
• Data packets:

Data packet	Direction	Length (bytes)	Description
<ITER>	client -> server	4	Number of trigger events/iterations
<PULSE_WIDTH>	client -> server	4	Pulse width (in units of 10ns)
<PERIOD>	client -> server	4	Time between trigger events (in units of 1ms)
LEN_0	client -> server	4	Trigger 0: length of the following data packet(in units of bytes)
DATA_0	client -> server	LEN_0	Trigger 0: concatenated 64 bit timestamps
LEN_1	client -> server	4	Trigger 1: length of the following data packet (in units of bytes)
DATA_1	client -> server	LEN_1	Trigger 1: concatenated 64 bit timestamps
...	...	...	...
LEN_<ITER - 1>	client -> server	4	Trigger <ITER - 1>: length of the following data packet (in units of bytes)
DATA_<ITER - 1>	client -> server	LEN_<ITER - 1>	Trigger <ITER - 1>: concatenated 64 bit timestamps

NOTE: The pulseGenCachedServer.py script caches all timestamps on local RAM. After receiving the data for the last trigger event the pulse generation is started.