Link

Setting up the board for Raspberry Pi acquisitions

How to connect

  1. Use the Rpi or Computer to connect to the FPGA
  2. Setup the jumper according to SPI master choice (USB or Rpi)
  3. Power up via a USB cable
  4. Configuration of the acquisition: send to FPGA the configuration registers via SPI
  5. Set the register EF to initiliaze memory (read and write pointers at 0)
  6. Start the acquisition, triging it up using the software, or with the onboard hardware trig button
  7. Do one SPI transaction and ignore the data received
  8. Read the measures via SPI

How to setup the board using only a RaspberryPi (here with RPi 4)

Putting the board together

Need a few feet to raise the board a bit above the ground, two 2x20 headers, and a SMA.

Board in a bag

What do we need ?

Assembled !

Software side

Updating the raspberry tools

You may need to install new packages, especially to communicate with the fpga.

sudo apt-get update
sudo apt-get install i2c-tools libasound2-dev python3-numpy python-numpy
sudo apt-get install python-dev libatlas-base-dev

From a general perspective, it may be worth trying to keep your tools up to date with:

sudo apt-get upgrade

If you face SPI / GPIOs issues, and that you are using a RPi4, you may want to follow these hints to update WiringPi. In short:

cd /tmp
wget https://project-downloads.drogon.net/wiringpi-latest.deb
sudo dpkg -i wiringpi-latest.deb
gpio -v

to check you’re using v2.52 or above.

Updating the python tools

On the raspberry pi, use pip to install the following modules:

pip3 install smbus2 RPi.GPIO PyAudio matplotlib numpy scipy spidev

How to update the FPGA binary

  1. Use a PC with (for example) diamond programmer or (preferred ;) ) using iceprog.
  2. Setup the the jumper for FPGA update (on J23, equivalent or Jumper4, named “SPI FT if IN”)
  3. Connect the USB
  4. Program via (for example) the diamong programmer application
  5. The LED program shall be lit when programmed successfully.

Installing iceprog to flash the fpga

iceprog is the software used to put the fpga on the flash storage on the board, which will be read by the fpga on boot. The easiest way is to :

sudo apt install fpga-icestorm

If this doesn’t work, then this may work:

sudo apt-get install libftdi-dev git gcc 
git clone https://github.com/cliffordwolf/icestorm.git
cd iceprog
make 
sudo make install

This will create and install the iceprog utility, used to flash the fpga program (bitstream).

Prepare the jumper here :

Then, plug an usb cable from the RPi to the board (not connected using the raspberry pi header).

Check that the FTDI device is well created by typing:

dmesg

and then flash the FPGA by doing:

wget https://github.com/kelu124/un0rick/raw/master/bins/v1.1.bin
iceprog v1.1.bin

This should flash the board:

If you do not have a success here, you may want to have a look at how to connect FTDI devices to your computer (see for example: https://stackoverflow.com/questions/36633819/iceprog-cant-find-ice-ftdi-usb-device-linux-permission-issue ). Usually, one has no issues with RPi fresh out of the box.

Physical setup / connections for the lib acquisitions

Pinouts

Raspberry Pi header

FTDI breakout

Setup

You can use a RPi4 with a ribbon cable to connect to the board, leaving the jumper on, putting one to select the high voltage level, connecting a piezo.. and that’s it.

Running an acquisition

Testing the connection to the board

Then, for example to discover the board using Python, you can use the library:

git clone https://github.com/kelu124/pyUn0-lib.git
cd pyUn0-lib
python pyUn0.py test

It will download the lib, then you should see with the ‘test’ option a LED blink

Testing the connection to the board

The “single” option will allow you to capture a single line, then the “process” one will create the corresponding images.

python pyUn0.py single
python pyUn0.py process

Results

I’ve used this exact setup to get the lib examples ( https://github.com/kelu124/pyUn0-lib ).

Example of an acq :

with a clean spectrum:

# Details of the RPi binary registers and specificities

Does not work with the USB binary!

You don’t need to read all of this, this is included in this version of the python lib.

FPGA setup

SPI is used to configure the DAC values every 5us, using the following addresses and protocol (SPI is only 8bits per CS). For each address:

  • Send 0xAA to access parameters
  • Followed by Send @ the address over 8 bits
  • Followed by Send Data, a parameter over 8 bits

Addresses start at 0xE0 and end at 0xD0 on the default bitstream.

Details of adresses to setup the board

Address Name of variable Size (bits) Description Default value in hex unit Value
0xE0 sEEPon 8 Lengh of Pon 0x14 10ns 200 ns
0xD0 sEEPonPoff 8 Lengh between Pon and Poff 0x0A 10ns 100 ns
0xE1 sEEPoff 8 Lengh of Poff MSB      
0xE2 sEEPoff 8 Lengh of Poff LSB 0xC8 10ns 2000 ns
0xE3 sEEDelayACQ 8 Lengh of Delay between Poff and Acq MSB 0x02BC 10ns 7000 ns
0xE4 sEEDelayACQ 8 Lengh of Delay between Poff and Acq LSB      
0xE5 sEEACQ 8 Lengh of acquisition MSB 0x32C8 10ns 130 us
0xE6 sEEACQ 8 Lengh of acquisition LSB      
0xE7 sEEPeriod 8 Period of one cycle MSB 0x186A0 10ns 1 ms
0xE8 sEEPeriod 8 Period of one cycle 15 to 8      
0xE9 sEEPeriod 8 Period of one cycle LSB      
0xEA sEETrigInternal 1 Software Trig : Auto clear 0 N/A  
0xEB sEESingleCont 1 0: single mode 1 continious mode 0 N/A  
0xEC sEEDAC 8 Voltage gain control: 0V to 1V 0x11 0,004 68 mV
0xED sEEADC_freq 8 Frequency of ADC acquisition 0x03 64/(1+f) MHz 16 MHz
0xEE sEETrigCounter 8 How many cycles in countinious mode 0x0A cycles 10 cycles
0xEF sEEpointerReset 1 Sofware memory reset: set to 1; auto clear 0    

How to read from the FPGA

SPI is used to read the ADC value. SPI in the case of the basic program is only 8 bits per CS.

Master send 0. If the FPGA is doing an acquisition, the returned value is 0xAA, else the value is on 2x8 bits.

  • MSB
    • 8th bit: MSB ID: set to 1
    • 6-7th bit: cycle bits: to identify a line in a sequence
    • 4-5th bits: the two inputs (TopTurn 1 and TopTurn2) in case a counter is used.
    • 1st-3th bits: ADC 7 to 9: 3 remaining bits of acquisition
  • LSB
    • 8th bit: LSB ID: set to 0
    • 1st to 7th bits: ADC 7-0: 7 first bits of acquisition

If the master reads more data than the board has acquired, SPI will return old or incorrect values: the master has to know how many measures were done.

DAC Configuration

SPI is used to configure the DAC values every 5us, using the following addresses and protocol (SPI is only 8bits per CS). For each register setup, you will have to send:

  • Send 0xAA to tell the board you’ll be setting a register
  • Followed by Send @ the address over 8 bits
  • Followed by Send Data, a parameter over 8 bits

Addresses start at 0x10 and end at 0x38. This corresponds to t = 0us for 0x10, and t = 200us for 0x38. Data range from 0 to 8 bits for full amplification.

TGC use

The gain was measured to check if it was working and yielded this gain curve according to the value put into the DAC.