Raspberry PI Based FPGA Test System Part One

Introduction

Previous projects have seen us develop a embedded system tile which contains a Spartan 7 FPGA. One thing I have wanted to do for a long time is develop a carrier card which will enable the prototyping of the applications running on the embedded system tile.

This carrier card would enable the embedded system tile to be controlled and stimulated from an external controller and to provide the embedded system tile with interfacing, the USB connector and of course clocks and power.

We also wanted the carrier card to be standalone such that it could automate tests and provide significant processing resources such that it could run complex and challenging programs.

As such we decided the tile carrier card would include a Raspberry PI Compute Module 5.

Decision Decisions

If you are not familiar with it the Raspberry PI CM5 is a powerful System-on-Module (SoM) designed to bring the capabilities of the Raspberry Pi 5 to embedded and industrial applications.

Key Features and Specifications

• Processor: At its core is the Broadcom BCM2712, a quad-core 64-bit Arm Cortex-A76 SoC clocked at 2.4GHz. This is the same high-performance processor found in the Raspberry Pi 5, offering a substantial leap in computational power.
• Memory: The CM5 is available with LPDDR4X SDRAM in configurations of 2GB, 4GB, and 8GB, with 16GB variants expected in 2025, providing ample memory for demanding applications. ECC (Error-Correcting Code) support is also included for enhanced reliability.
• Storage: Onboard eMMC Flash storage options include 16GB, 32GB, and 64GB. A "Lite" version with 0GB eMMC is also available, allowing for external storage solutions via SD card or NVMe. 128GB eMMC variants are anticipated in 2025.
• Graphics: It features an 800 MHz VideoCore VII GPU, supporting OpenGL ES 3.1 and Vulkan 1.2, enabling robust multimedia and display capabilities.
• Connectivity:
• Wireless (Optional): Integrated 2.4 GHz / 5.0 GHz IEEE 802.11 b/g/n/ac Wi-Fi and Bluetooth 5.0, BLE, with an electronic switch for internal PCB trace or external antenna.
• Ethernet: Onboard Gigabit Ethernet PHY with IEEE 1588 support for precise time synchronization.
• PCIe: A 1x PCIe x1 Gen 2 root complex (5Gbps), commonly used for high-speed peripherals like NVMe SSDs via an M.2 M-key socket on carrier boards
• USB: Two USB 3.0 ports (5Gbps simultaneous operation) and one USB 2.0 port (high speed).
• Video Interfaces: Two HDMI 2.0 ports capable of simultaneously driving dual 4Kp60 displays.
• Camera/Display Interfaces: Two 4-lane MIPI ports, configurable for either DSI (display) or CSI-2 (camera).
• General Purpose I/O (GPIO): Up to 30 configurable GPIO pins, supporting 1.8V or 3.3V signaling, with a wide range of peripheral options including UART, I2C, SPI, SDIO, DPI, I2S, and PWM.

All of this is provided in a small 55mm x 40mm form factor, although it does require passive thermal management e.g. a heat sink.

Architecture

The tile carrier board is design to prototype the embedded system tile of which there is a planned range of different devices and capabilities.

As such the architecture of the tile must be just right. the architecture therefore provides

• Direct JTAG access to the tiles JTAG Pins
• USB JTAG access via USB C
• USB C Access to a FTDI 4232H mapped to the FPGA tile IO ring,
• Sky works clock generator connected to dedicated clock inputs on the FPGA Tile IO ring. This is configurable using a external programmer or via the CM5
• Two Pmods connected to the FPGA tile IO ring for interfacing with external peripherals
• USB C access directly to a FPGA pins to enable development of FPGA USB solutions.
• USB C access to the RPI CM5 for configuration and set up
• GPIO connections between the FPGA Tile IO ring and the RPI CM5
• Ethernet, WiFi, BlueTooth, 2 MIPI CSI/DSI interfaces, Dual HDMI and Dual USB A provided by the RPI CM5

One of the more interesting architectural decisions while we mostly use FTDI devices for UART, or JTAG. They can also be used for bit banging, SPI and I2C. being connect

The complete architecture looks as below

The completed board looks as below.

Configuring the Raspberry PI Compute Module 5

This was the first time I have brought up a Raspberry PI Compute Module 5, to do this we need to use the USB C. If we designed the board right the USB C is connected to the CM5 USB 2 interface, the hardware design also needs to have included a pull down signal on nRPI_Boot so we can place the CM5 in the correct mode and prevent it from booting from the as yet unprogrammed eMMC.

We also need a couple of software applications the first is the Raspberry PI USB Boot Setup this allows our machine to be able to detect a RPI including the CM5 over the USB and correctly open it in the right format as a drive. Just like we get when we plug a thumb drive into our machine. While the second is the Raspberry Pi imager.

Both are available here

Lets first install the USB Boot Set Up.

Click on Next.

Click on I Agree.

Click Next.

Select the boot location.

This might take a few minutes to install.

Once installed you will see the finish option.

The next step is to connect the CM5 module to the carrier card and power it on over the USB C. As we want to communicate using the USB C it is powered from a development machine.

You might want to place a heat sink on the CM5 which is what we did after this image was taken

Run the RPI Boot Set up to detect the CM5, I breathed a sigh of relief when it was detected as it meant our USB architecture was working.

Run the Raspberry PI imager and select the CM5 drive as the destination and RPI5 as the target operating system.

If desired you can edit the settings to configure settings like the WiFI etc.

It is OK to erase all the data on the eMMC

The writing will take a little while to prepare.

Eventually it will start writing

After a few minutes the image will be written to the card and we are read to try and power it up.

Checking the CM5 and Carrier Card

The next thing to do was to check the CM5 Interfaces, power cycling the board means the CM5 will boot into the Raspbian operating system.

Connecting the HDMI should mean we are able to see a desktop, from both HDMI outputs. We should also be able to connect a mouse using the USB A and if we wanted a web cam. Of course we also have the MIPI camera connectors also.

To get started I plugged in the monitor to HDMI 0, and a USB Bluetooth keyboard and mouse.

With this and with the setting of the WiFi Password for the office earlier the board jumped to life.

Connecting the monitor to both HDMI ports resulted in video being output on both though I think in reality we will only use for most applications.

While I configured the CM5 to connect to the WiFi, I also connected the Ethernet port to ensure the wired connection works as expected.

Of course to be able to develop our test applications for the FPGA we want to be able to connect remotely and apply tests to the FPGA tile. To be able to do this we need to be use Raspberry PI Connect.

The first step is to install the rpi-connect package.

Once we have the connect up and running and have signed in on the CM5 we can access the board remotely from our development machine.

Wrap Up

This project has demonstrated the design of a custom CM5 Carrier card and its initial bring up. There is still a little way to go, with getting the FPGA up and running for test applications. But I think so far the board looks good and is ready to begin that journey, which we will cover in another project soon.