Product guide of the imperix firmware IP

This page documents the imperix firmware IP for AMD/Xilinx Vivado, which is required to program the FPGA of imperix controllers. This IP encapsulates the imperix proprietary FPGA logic and offers various interfaces allowing users to add their own custom logic around it.

The document details the different signals provided by this IP, along with their associated timings. Separate documentation exists for specific interfaces, as listed in the table below:

Interface	Feature/objective	Product note
ADC	Retrieving ADC conversion results as soon as they are available.	PN126
SBIO	Exchanging data between the user code running in the CPU and the FPGA.	PN128
SB-PWM	Driving the PWM output chain, comprised of a dead-time generation system and the hardware protection mechanisms.	PN127
USR	Accessing physical 3V3 I/O pins.	PN179
GT	Accessing Gigabit Transceivers (GT), enabling support of protocols such as Aurora on SFP ports.	PN118
BSCAN	Using ILAs to observe FPGA signals in real-time for debugging purposes.	PN129

Architecture overview

Because FPGA development operates at the hardware level, a thorough understanding of the underlying system architecture and real-time execution behavior is essential for successfully integrating custom logic into the FPA of an imperix controller.

• The article PN253 presents the architecture of imperix controllers, explains their main data paths, and introduces the key subsystems. Fundamental information regarding how the controllers manage control-relevant clocks and timing is also provided.
• The article PN261 explains how imperix controllers operate and details the typical sequence of acquisition → processing → modulation through the user-programmable CPU. Information is also provided about the core operating states and the related enabling/disabling of PWM outputs.

Imperix actively supports two controller generations, both based on AMD Xilinx System-on-Chips (SoCs):

• Gen 3 controllers (B-Box 3, B-Box Micro, B-Board PRO, TPI8032) are based on an AMD Zynq 7000
• Gen 4 controller (B-Box 4) is based on an AMD Zynq Ultrascale+

While the specifics (number of CPUs, clock speeds, FPGA resources, etc.) vary between the generations, the operating principles and control workflow are identical. The global architecture is also similar, as shown below:

The core modules contained within the imperix firmware IP are:

• The data acquisition module (documented in PN126) pilots the ADC chips and makes the analog input measurement available to both the CPU user app and the user-programmable FPGA area.
• The pulse-width modulation (documented in PN127) contains the pre-implemented PWM modulators (CB, SV, DO, SS, PP). It allows driving the PWM outputs from a custom modulator using the SB-PWM path.
• The CLK module manages the main clock CLK0 (configured via the CONFIG block) and the optional CLK1, CLK2 and CLK3 (configured via CLK block).
• The DMA is responsible for transferring the data between the FPGA and the CPU read/write buffers. The read and write phases are detailed in the next section.

Execution timing & signals

The following figures illustrate the key phases involved along the CPU control path. These are detailed in PN261, and summarized below:

• Acquisition: covers the physical Analog-to-Digital conversion and data retrieval to the FPGA fabric.
• Read: represents the data transfer from the FPGA to the CPU read buffer.
• CPU task: contains the execution of the main control task (user-defined control algorithms).
• Write: represents the data transfer from the CPU write buffer to the FPGA.

Interestingly, a second data path exists, associated with the FPGA task, that permits control algorithms to be fully executed on the FPGA, as in the control example presented in TN147.

On the PL side (FPGA), the imperix firmware IP provides several signals to monitor and synchronize logic during the execution of these phases.

Port name	Clk domain	Description
sampling_pulse	clk_250_mhz	Indicates the ADC sampling instant and the start of the acquisition phase. Corresponds to the rising edge of the sampling clock SCLK.
adc_done_pulse	clk_250_mhz	Indicates that the acquisition phase is finished and new ADC values are available at the ADC interface.
adc_done_cpu_pulse	clk_250_mhz	When the sampling rate differs from the CPU rate, this signal is a decimated version of adc_done_pulse. It is set when the CPU control path stages are scheduled to execute. The following section describes this scenario in more detail.
reading	clk_250_mhz	Indicates that the system is in the read phase, in which data flagged as real-time (SBI registers, ADC, GPI, etc.) are sent to the CPU read buffer.
data_valid_pulse	clk_250_mhz	Asserted at the end of the write phase, notifying that new data were written (SBO registers, PWM duty-cycles, GPO, etc.).

Handling different execution rates

FPGA-based control algorithms are often desired to execute at a higher rate than the CPU. In such cases, a postscaler can be configured in the CONFIG block to reduce the CPU rate relative to the sampling frequency. Then, the adc_done_cpu_pulse acts as the decimated version of adc_done_pulse. It is asserted when the CPU control path stages are scheduled to run.

Differences between Gen. 3 and Gen. 4 devices

For FPGA development, the B-Box 4 offers several key enhancements over its predecessors, such as access to analog measurements in floating-point format, faster transceivers, and expanded FPGA resources. The table below summarizes the key differences between the two generations.

Component	Gen 3	Gen 4
FPGA	Kintex 7 125K	Kintex US+ 504K
Logic	LUTs: 78600 Registers: 157200	LUTs: 230400 Registers: 460800
Logic used by imperix IP*	min: LUTs: 25482 (32.4%) Registers: 46374 (29.5%) max: LUTs: 39143 (49.8%) Registers: 67203 (42.7%)	min: LUTs 70733 (30.7%) Registers 108749 (23.6%) max: LUTs: 94233 (40.9%) Registers: 140636 (30.5%)
Usable logic left*	max: LUTs: 53118 (67.6%) Registers: 110826 (70.5%) min: LUTs: 39457 (50.2%) Registers: 89997 (57.3%)	max: LUTs: 159667 (69.3%) Registers: 352051 (76.4%) min: LUTs: 136167 (59.1%) Registers: 320164 (60.5%)
Gigabit Transceivers available from the sandbox	3x GTX (3x SFP connectors) Up to 6.6 Gbps	4x GTH (1x QSFP connector) Up to 16.3 Gbps
Bidirectional direct FPGA I/Os (USR)	36x	36x
PWM outputs	32x	48x
ADC interface	16x (int16)	24x (int16, or float)
RS485/RS422	–	2x
Acquisition delay	2 μs (B-Box RCP 3.0) 500 ns (B-Box Micro, B-Board, TPI8032)	200 ns / 368 ns**

* The logic used by the imperix IP depends on the enabled features, as explained in the Disabling Features to Save FPGA Resources section.

** When channels A12-A23 are used.

Interface description of the firmware IP

ADC interface

The ADC interface returns the raw 16-bit signed integer result from the ADC chips. Practical guidance for retrieving data from ADCs is provided in PN126.

Port Name	Direction	Width	Clk domain	Description
ADC_reg_XX	Output	16bits	clk_250_mhz	ADC 16-bit result in 2’s complement format. XX = channel
adc_done_pulse	Output	1 bit	clk_250_mhz	Indicates that new ADC samples are available.
adc_done_cpu_pulse	Output	1 bit	clk_250_mhz	Decimated version of adc_done_pulse when a postscaler is used. Set when the CPU control path stages are scheduled to run.

ADC_FLOAT interface

Available exclusively on the B-Box 4, this interface provides access to the true physical values, in single-precision floating-point format, as they are available at the end of the ADC signal chain. The rescaling from the raw 16-bit ADC value is configured by setting the sensor sensitivity and offset from the ADC block.

Port Name	Direction	Width	Clk domain	Description
ADC_FLOAT_reg_XX	Output	32bits	clk_250_mhz	ADC floating-point result post rescaling. XX = channel
adc_done_float_pulse	Output	1 bit	clk_250_mhz	Indicates that new ADC_FLOAT samples are available.
adc_done_cpu_float_pulse	Output	1 bit	clk_250_mhz	Decimated version of adc_done_float_pulse when a postscaler is used. Set when the CPU task is scheduled.

SBIO interface

The SBIO_BUS (SandBox IO Bus) is a 16-bit memory-mapped bus allowing the CPU to address up to 1024 registers in the FPGA. This bus is dedicated to user-configured data exchanges between the CPU and the FPGA. Its Simulink/PLECS counterparts are the SBI/SBO blocks. Specific documentation is provided in PN128.

Port Name	Direction	Width	Clk domain	Description
SBIO_BUS_sb_addr	Output	10 bits	clk_250_mhz	Address of the accessed register
SBIO_BUS_sb_we	Output	1 bit	clk_250_mhz	Write enable
SBIO_BUS_sb_wdata	Output	16 bits	clk_250_mhz	Write data
SBIO_BUS_sb_rdata	Input	16 bits	clk_250_mhz	Read data

The bus performs read operations by setting the requested address on sb_addr and expects the corresponding data on sb_rdata exactly four cycles later.

A write occurs on each rising edge of clk when sb_we is asserted. The target location is given by sb_addr and the value written is sb_wdata.

The two additional signals listed below are provided to help synchronize custom logic with the SBIO bus operations:

Signal	Direction	Width	Clk domain	Description
reading	Output	1 bit	clk_250_mhz	Asserted high while data (ADC, SBI, GPI) are being read by the CPU.
data_valid_pulse	Output	1 bit	clk_250_mhz	Single-cycle pulse indicating that all SBO registers have been written for the current CPU control task.

SB-PWM interface

The SB-PWM (SandBox-PWM) interface allows PWM outputs to be driven from custom FPGA logic while still benefiting from the controller’s hardware protections. Additionally, when using the SB-PWM interface, users also benefit from existing dead-time generation and enable/disable mechanisms similar to driving PWMs from the SB-PWM block (or similar). This interface is further documented in PN127.

Port Name	Direction	Width	Clk domain	Description
sb_pwm	Input	48 bits (Gen 4) 32 bits (Gen 3)	clk_250_mhz	PWM signals driven from sandbox logic.

CLOCK interfaces

The CLOCK interface provides access to the four user-configurable time clock generators. More information about these resources is provided in PN253. Typical timing configurations are also presented in PN259. On the practical side:

• The main clock CLOCK_0 must be configured via the CONFIG block
• The auxiliary clocks, CLOCK_1, CLOCK_2 and CLOCK_3 must be configured via the CLK blocks.

Port Name	Direction	Width	Clk domain	Description
CLOCK_N_period	Output	16 bits	clk_250_mhz	Period of the clock in ticks.
CLOCK_N_prescaler	Output	16 bits	clk_250_mhz	Indicates the CLOCK_N_timer ticking rate. 1 tick = 4 ns * CLOCK_prescaler.
CLOCK_N_timer	Output	16 bits	clk_250_mhz	Timer counting from 0 to CLOCK_period-1 at the ticking rate set by the CLOCK_N_prescaler.
CLOCK_N_clk_en	Output	1 bit	clk_250_mhz	Clock enable pulse indicating when CLOCK_N_timer is updated.

Interestingly, the prescaler extends the achievable frequency range beyond what the 16-bit period timer counter alone can provide. With CLOCK_N_prescaler = 1, the minimum achievable frequency is approximately 3.8 kHz (250 MHz / 65535). For lower frequencies, the CLOCK_N_prescaler automatically increases, and the firmware tries to closely match the requested frequencies.

Example:

• A frequency of 20 kHz results in CLOCK_prescaler = 1 and CLOCK_period = 12500 ticks.
• A frequency of 2 kHz results in CLOCK_prescaler = 2 and CLOCK_period = 62500 ticks.

When prescaler = 1:

• clk_en is asserted every clk_250_mhz cycle
• CLOCK_0_timerincrements on every clock edge

When prescaler > 1:

• clk_en is asserted once every X cycles (where X = prescaler value)
• CLOCK_0_timer increments only when clk_en is high

GT interfaces

The Gigabit Transceiver (GT) interface provides access to high-speed serial transceivers connected to the SFP+, respectively QSFP+ sockets. This enables custom point-to-point communication with external devices such as other controllers, custom hardware etc.

PN118 is an example setting up loopback communication using Xilinx/AMD Aurora as a communication protocol. Additional examples with third-party hardware-in-the-loop (HIL) simulators (OPAL-RT, Plexim and RTDS) are provided on the page SFP communication with third-party devices.

Feature	Gen 4	Gen 3
Available transceivers	4x GTH (1x QSFP connector, lanes 4–7)	3x GTX (3x SFP connectors)
Maximum line rate	16.3 Gbps	6.6 Gbps

Accessing GTH transceivers on Gen 4 controller

On Gen 4, lanes can be exposed to the sandbox from the Configuration tab in the imperix firmware IP configuration. Each enabled lane exposes the following signals:

Port Name	Direction	Description
GT_USER_TX_N_txp	Output	Transmit positive (differential)
GT_USER_TX_N_txn	Output	Transmit negative (differential)
GT_USER_RX_N_rxp	Input	Receive positive (differential)
GT_USER_RX_N_rxn	Input	Receive negative (differential)
gt_refclk	Output	250 MHz reference clock (shared across all lanes)

Accessing GTX transceivers on Gen 3 controller

On Gen 3, the SFP ports are used by default for RealSync inter-device communication. Using a port from the sandbox requires disabling RealSync on that specific link, which removes the inter-device communication capability on that port. Lanes can be exposed to the sandbox from the Configuration tab in the imperix firmware IP configuration. Each enabled lane exposes the following signals:

Port Name	Direction	Description
txp_N	Output	Transmit positive (differential)
txn_N	Output	Transmit negative (differential)
rxp_N	Input	Receive positive (differential)
rxn_N	Input	Receive negative (differential)

Serial port interfaces

The serial port interfaces are exclusive to the B-Box 4 and are typically used by the pre-implemented SSI, BiSS-C and EnDat2.2 FPGA drivers. The imperix IP allows bypassing these built-in drivers by providing direct access to RS485/RS422 transceiver signals from the sandbox, as illustrated below.

The serial ports (A and/or B) can be made available from the sandbox from the Configuration tab in the imperix firmware IP configuration. Each enabled serial port exposes the following signals:

Port Name	Direction	Description
SERIAL_X_rx	Input	Receive data from external device
SERIAL_X_tx	Output	Transmit data to external device
SERIAL_X_clk	Output	Clock signal for synchronous protocols
SERIAL_X_en	Output	Transceiver enable (active high)

BSCAN Interface to observe internal signals using ILA

The BSCAN (Boundary Scan) interface exposes the FPGA’s debug scan chain to the sandbox and enables the use of Integrated Logic Analyzers (ILAs) and other Xilinx debug cores. When combined with the Xilinx Virtual Cable (XVC) protocol, this allows remote debugging of internal FPGA signals directly from Vivado’s Hardware Manager over Ethernet.

For detailed instructions on adding ILAs to your design and connecting to them via XVC, refer to PN129.

Digital I/Os drivers

The sandbox exposes various digital I/O signals. Some ports are available for user logic, while others are reserved for internal system operation and must not be modified. For detailed pin locations and electrical specifications, refer to the relevant datasheet:

• B-Box 4 datasheet
• B-Box RCP datasheet
• B-Box Micro datasheet
• B-Board PRO datasheet
• TPI 8032 datasheet

The USR pins

The USR pins are 36 user-configurable 3.3V I/Os routed directly to the FPGA, without any resistors or level shifters on the PCB traces. These pins are typically used for interfacing external peripherals (e.g., SPI ADC) but can, in fact, be leveraged for a very broad range of applications, thanks to their bidirectionality and high bandwidth.

More information about accessing USR pins is provided in PN179.

Port Name	Direction	Description
USR[35:0]	Tristate	These pins are used by the motor interface and the programmable inverter. When none of these devices are in use, the USR pins can freely be accessed from the sandbox.

Private Ports

These ports are required for internal communication with controller components and are reserved for imperix use. Modifying these connections may cause undefined behavior and must be absolutely avoided.

Port Name	Direction	Description
private_in	Input	Internal system signals. Width varies by generation.
private_out	Output	Internal system signals. Width varies by generation.
DDR	–	DDR memory interface
FIXED_IO	–	Fixed I/O interface to PS

Gen 4 ports

Port Name	Direction	Description
din[23:0]	Input	General-purpose or fault feedback inputs (GPI/FLT)
dout[47:0]	Output	General-purpose outputs or PWM outputs (GPO/PWM)

Gen 3 ports

Port Name	Direction	Clock Domain	Description
flt[15:0]	Input	clk_250_mhz	Fault inputs
gpi[15:0]	Input	clk_250_mhz	General-purpose inputs
gpo[15:0]	Output	clk_250_mhz	General-purpose outputs
pwm[31:0]	Output	clk_250_mhz	PWM output signals
BBOX[51:0]	Tristate	N/A	Internal B-Box RCP pins. Can be repurposed on B-Board PRO with custom PCB design (see PN201).

Disabling features to save FPGA resources

The imperix firmware IP includes several optional features that can be disabled to free up FPGA resources for custom sandbox logic. Access the resource-saving options from the Saving FPGA resources tab in the imperix firmware IP configuration.

Disabling a feature removes it entirely from the FPGA design. If the corresponding functionality is used in the CPU model, an error will be raised in Cockpit. Additionally, unused modulators can be removed to save logic resources. Notably, the CB-PWM logic can be disabled in groups of 8 lanes.

Feature	Gen 4	Gen 3
CB-PWM lanes 0–7	✓	✓
CB-PWM lanes 8–15	✓	✓
CB-PWM lanes 16–23	✓	✓
CB-PWM lanes 24–31	✓	✓
CB-PWM lanes 32–39	✓	—
CB-PWM lanes 40–47	✓	—
SS-PWM logic	✓	✓
PP-PWM logic	✓	✓

Resource Savings

Feature	Gen 4	Gen 3
CB-PWM (per 8 lanes)	~2100 LUTs (0.9%) ~2800 Registers (0.6%)	~1600 LUTs (2.03%) ~2000 Registers (1.27%)
SS-PWM	~6250 LUTs (2.71%) ~5500 Registers (11.93%)	~2700 LUTs (3.43%) ~3300 Registers (2.1%)
PP-PWM	~4400 LUTs (1.9%) ~9200 Registers (2%)	~4400 LUTs (5.6%) ~9150 Registers (5.82%)