UniMon Gateware Documentation

This documentation was automatically generated from the Markdown file README.md in the Git repository https://git.gsi.de/BEA_HDL/UniMon_Gateware
Any changes should be applied to the Markdown file, which can be converted to DokuWiki format using the script FPGA_Common/doc/scripts/create_dokuwiki.py.

The documentation is also available as a PDF: UniMon_Gateware_Documentation.pdf

An up to date PDF version can be downloaded from the CI/CD section: https://git.gsi.de/BEA_HDL/UniMon_Gateware/-/pipelines.

Documentation that is common to multiple FPGA based projects can be found here: FPGA Common Documentation. It is also available as a PDF: FPGA_Common_Documentation.pdf

The code of this project and also the source of this documentation are under version control in a Git repository whose upstream is:
https://git.gsi.de/BEA_HDL/UniMon_Gateware.
The relevant branch is master.

Common code is included as a Git submodule of the main Git repository. The upstream of the submodule is:
https://git.gsi.de/BEA_HDL/FPGA_Common.
The relevant branch is master.

Installation scripts to set up a Gitlab runner for continuous integration including all necessary software to build the gateware can be found in a Git repository whose upstream is:
https://git.gsi.de/BEA_HDL/Gitlab_Runner_Setup_Centos_7.
The relevant branch is master.

This document describes the gateware (= FPGA firmware) implementation of the UniMon Tank Signal Monitor.

The system uses 4 IOxOS ADC_3117 FMC cards which are mounted on two OpenHardware AFC v4.0 FMC carriers. Each of the FMCs provides 20 ADCs with a resolution of 16 bits. The sampling rate of the ADCs is adjustable between 1 kHz and 5 MHz. Each ADC input is individually configurable as a differential or single ended and different gain settings are available.

Figure 1.1: UniMon crate in the HKR

The gateware of each AFC stores the data stream of respectively 40 ADCs to a ring buffer, from which it can be read via PCIe.

This project incorporates the code from the FPGA_Common Git repository which is used in multiple projects. The documentation of the common features can be found here:

Documentation about the register bank, the architecture information storage and the observer can be found here:
https://git.gsi.de/BEA_HDL/FPGA_Common#2-common-monitoring-and-control-features

There is a expert GUI that can be used together with multiple projects:
https://git.gsi.de/BEA_HDL/FPGA_Common#3-fpga-observer

You can find instructions on how to build and simulate the gateware here:
https://git.gsi.de/BEA_HDL/FPGA_Common#4-build-flow-and-simulation

You can find usefull scripts here:
https://git.gsi.de/BEA_HDL/FPGA_Common#5-helper-scripts

Information about the continuous integration setup can be found here:
https://git.gsi.de/BEA_HDL/FPGA_Common#6-continuous-integration-environment

You can find instructions on how to program the FPGA and configure other hardware here:
https://git.gsi.de/BEA_HDL/FPGA_Common#7-programming-and-hardware-configuration

The gateware communicates with the following devices on each of the IOxOS ADC_3117 FMC cards:

• 10 * Analog Devices LTC2323-16 dual ADC
• 10 * EXAR XRA1405 GPIO expander

Each LTC2323-16 consists of two ADCs that are sampled in parallel.

The sampling frequency is adjustable in the range between 1 kHz and 5 MHz.

Each ADC provides a differential input pair and is directly controlled by the FPGA without any external clock.

The FPGA has to read the samples at a clock speed of 105 MHz. The sampling rate of the ADCs is controlled by the distance between the so called conversion pulses that have to be generated by the FPGA [1].

Due to this clock generation logic of the ADCs, the sampling frequency can be set with a certain granularity described in chapter 6.2.2.1.

The GPIO expanders are used for multiple purposes. Among these is the control of the inputs to each ADC.

There are dedicated switch devices in front of each of the differential ADC inputs, which can be controlled independently.

The following input settings are available:

• differential p / n input pin
• ground
• configurable calibration voltage (not implemented yet)
• fixed calibration voltage of + 4.128 V

The gain of each differential ADC input pair can be controlled by a dedicated fixed gain amplifier device which can be programmed to an amplifications of 1, 2, 5 or 10.

In front of each ADC input there is an attenuator with a fixed gain of 0.4.

In total the following gains are available [2]:

amplifier gain	input range	resolution per LSB
1	+/- 10.24 V	312.5 V
2	+/- 5.12 V	156.25 V
5	+/- 2.048 V	62.5 V
10	+/- 1.024 V	31.25 V

The gateware uses only one primary clock.

The PCIe reference clock has a nominal frequency of 100 MHz and feeds the reference clock input of the PCIe IP core by Xilinx, which contains a PLL producing a 125 MHz output clock for the AXI interface named clk_125_pcie_axi.

clk_125_pcie_axi drives a MMCM to generate:

• clk_100, 100 MHz, this is the main processing clock of the design
• clk_200, 200 MHz, used for the SDRAM interface IP core by Xilinx
• clk_50, 50 MHz, used for generating a 210 MHz clock for the ADC interface

The SDRAM interface IP core contains a MMCM which generates a 100 MHz clock named clk_100_sdram for the AXI interface.

As long as the PLL in the MMCM producing the main processing clock clk_100 is not yet in lock, the design is held in reset. After this the lock should be stable until the next power cycle.

The design will be reset whenever the PCIe connection is re-initialized. This happens e.g. when the FEC is rebooted.

There is a push button labeled RST at the center of the AFC front panel which is connected to the microcontroller for the MMC firmware. The OpenMMC firmware forwards a button press with a duration of at least two seconds to the FPGA pin AG26 as an active low signal to initiate a reset of the gateware.

Resetting the FPGA leads to the loss of the PCIe connection. To re-enable the connection, the FEC has to be rebooted.

Figure 4.1: Simplified data flow diagram

Figure 4.1 shows a simplified data flow diagram. For simplicity, some features are not included in the diagram:

• processing clocks and clock domain crossings
• resets
• LEDs
• read out logics of FPGA serial number and build time stamp
• data width conversions of AXI connections

This gateware uses the Xilinx IP core DMA/Bridge Subsystem for PCI Express with the following configuration:

• PCIe speed: 5 GTransfers/s
• AXI clock frequency: 125 MHz
• reference clock frequency: 100 MHz

The PCIe reference clock is routed to the FPGA via the MMC firmware and is configured to be driven by the 100 MHz FCLKA clock coming from the AMC connector.

For the communication with the SDRAM, an IP core by Xilinx is used. The clock frequency of the SDRAM interface’s AXI bus is 100 MHz, but has a different source so that an AXI clock converter is used to connect it to the rest of the AXI infrastructure which is clocked at the main processing clock of 100 MHz.

This project incorporates the observer interface from the FPGA_Common Git submodule (see https://git.gsi.de/BEA_HDL/FPGA_Common#13-observer).

The following signals are connected to the observer inputs:

The rest of the multiplexer inputs are connected to zero.

The communication between the gateware and the software takes place via a PCIe driver by Xilinx called XDMA. There is only one PCIe Bar in use in the gateware which maps the memory space to different physical memories on the AMC board.

The following mapping is applied:

Table 5.1: Memory mapping

The architecture information and the observer are documented here:
https://git.gsi.de/BEA_HDL/FPGA_Common#2-common-monitoring-and-control-features

Read and write accesses are mapped to virtual file accesses:

• /dev/xdma0_c2h_0 for read accesses
• /dev/xdma0_h2c_0 for write accesses

Example in C:

uint32_t address = 0x00000000;
int fd = open("/dev/xdma0_c2h_0", O_RDWR);
lseek(fd, address, SEEK_SET);
uint64_t value;
read(fd, &value, sizeof(uint64_t));

It is important to write the whole register width of 64 bits. If a register has less than 64 bits, the unused MSBs have to be written to any value. 32 bit write accesses will not have any effect.

Example in C:

uint64_t value = 42;
uint32_t address = 0x00000400;
int fd = open("/dev/xdma0_h2c_0", O_RDWR);
lseek(fd, address, SEEK_SET);
write(fd, &value, sizeof(uint64_t));

Example in C:

uint32_t address = 0x80000000;
int fd = open("/dev/xdma0_c2h_0", O_RDWR);
lseek(fd, address, SEEK_SET);
char data[1024];
read(fd, data, 1024);

This example reads 1024 bytes of data to an array. For bigger data blocks, instead of using an array, you will probably prefer a dynamically allocated memory region.

The complete SDRAM is used for the scope memory. The ADC data is stored in the following format:

Table 5.2: ADC data storage format

The scope is a free running ring buffer. The write pointer is incremented with each incoming ADC sample vector by the vector size of 128 bytes.

The scope memory can hold up to samples. At the maximum sampling frequency of 5 MHz this corresponds to a maximum capture duration of 3.36 seconds.

The following status registers can be read by software:

Table 5.3: List of status registers

This register holds the latest ADC data sample.

Address where the next data sample will be stored during the scope’s capturing process. The recently stored ADC data can be found below this address, or - in case of a ringbuffer wraparound - also below the end of the memory region.

The communication to the SDRAM is controlled by an IP core by Xilinx which performs a timing calibration at start up. The value of this register will be 1 after completion of the initial calibration. If this registers reads 0, this might indicate that the SDRAM is damaged.

Time when the bitstream was created. This information can be used to identify the gateware version (together with the Git commit information documented in https://git.gsi.de/BEA_HDL/FPGA_Common#122-gateware-information).

Format:

The XDMA PCIe driver by Xilinx numbers the devices randomly and is not able to identify the slot number of an AMC board. This register holds the FPGA’s unique serial number and can be used to identify an AMC board.

The module ID can be used to identify the type of the current bitstream.
The module ID of the UniMon gateware is 0x0001010300010002.

The fields are defined as follows:

Here is an incomplete list of project IDs:

The magic number can be used to determine if the gateware uses the expected register format.
The value of this register is the same for all module IDs: 0xBADEAFFEDEADC0DE.

The following registers can be written by software:

Table 5.4: List of configuration registers

This parameter defines the sampling frequency of all 40 ADCs in parallel.

The sampling frequency is given by:

The allowed range for the sampling frequency is:

The default setting of 0 corresponds to a sampling frequency of 5 MHz.

The allowed range for is:

The signals from the timing receiver enter the FPGA via the MLVDS lines with virtually no delay, while the corresponding ADC samples will be delayed due to the sampling process.

This register can be used to add an additional delay to the signals from the timing receiver in order to calibrate them to the delays of the ADCs.

The delay can be chosen from the range . Each LSB corresponds to an additional delay of 10 ns.

There are programmable amplifiers in front of each ADC input, which provide four discrete gains.

The following gains are available:

value	gain	input range	resolution per LSB
0	1	+/- 10.24 V	312.5 V
1	2	+/- 5.12 V	156.25 V
2	5	+/- 2.048 V	62.5 V
3	10	+/- 1.024 V	31.25 V

This register holds the concatenation of the gain settings of the FMC’s 20 ADCs:

The ADCs have differential inputs. The two lanes p and n can be configured separately and individually for each ADC.

The following input settings are available:

This register holds the concatenation of the input settings of the FMC’s 20 ADCs:

Correction summand for a possible offset deviation of the ADC. The offset correction precedes the gain correction.

Correction factor for a possible gain deviation of the ADC. The default value 0x8000 corresponds to a multiplication by 1. The possible correction range is .

Writing a 1 to this register triggers a reset on the gateware, which also resets all configuration registers to their default values.
The reset will be automatically lifted so that the register does not have to be written to 0 after initiating a reset.

[1] Analog Devices LTC2323-16 datasheet, https://git.gsi.de/BEA_HDL/UniMon_Gateware/-/blob/master/doc/datasheets/AD_LTC2323_ADC_datasheet.pdf

[2] IOxOS ADC_3117 datasheet, https://git.gsi.de/BEA_HDL/UniMon_Gateware/-/blob/master/doc/datasheets/ADC_3117_UG.pdf