Exploring Ultrascale FPGA Configuration Methods: JTAG, QSPI, and eMMC

In our previous post, we explored the boot process of  AMD Ultrascale FPGAs, breaking down each phase from power-on reset to system initialization. Now, we shift our focus to another crucial aspect of FPGA operation: configuration methods. Different programming modes offer trade-offs in speed, flexibility, and production suitability, impacting how FPGAs are initialized in various applications.

Let’s examine three widely used FPGA configuration methods: JTAG, QSPI, and eMMC.

All of these configuration methods are available on our boards, such as:  PXIe720, SE120, SE125, PCIe104Z+, PCIe104Z, PCIe104-MAX

JTAG (Joint Test Action Group) Configuration

JTAG is primarily used for testing and debugging electronic circuits, but it also serves as a method for programming FPGAs.

How JTAG Works

  • JTAG uses a serial communication interface to transfer bitstream data into the FPGA.
  • The FPGA configuration occurs bit-by-bit, utilizing an internal shift register chain.
  • This method allows for precise control over individual configuration parameters.

Benefits

✅ High flexibility – Supports multiple configuration modes (master, slave, indirect).
✅ Debugging access – Provides visibility into internal FPGA logic for troubleshooting.
✅ Fine-grained control – Engineers can manipulate individual FPGA registers for detailed testing.

Drawbacks

❌ Slow speed – JTAG operates serially, making it less efficient for large FPGAs.
❌ Physical cable requirement – A JTAG cable must be connected during programming.
❌ Not ideal for production – Typically used during development rather than final deployment.

QSPI (Quad Serial Peripheral Interface) Configuration

QSPI is a high-speed serial interface commonly used for flash memory storage. It provides a faster and more compact FPGA programming method compared to JTAG.

How QSPI Works

  • The FPGA reads bitstream data from an external QSPI flash memory chip.
  • The data transfer rate is higher than traditional SPI, making configuration faster.
  • The FPGA automatically loads the configuration file upon startup.

Benefits

✅ Fast programming speeds – Much faster than JTAG, ideal for large FPGAs.
✅ Non-volatile storage – Bitstream data remains stored in flash memory even after a power cycle.
✅ Compact implementation – Uses fewer FPGA pins compared to JTAG.
✅ Well-suited for production – Commonly used for high-volume deployments.

Drawbacks

❌ Less flexible – QSPI provides less control over the configuration process than JTAG.
❌ Requires external memory – Needs a dedicated QSPI flash chip.
❌ Potential for configuration failures – If the bitstream in flash memory is corrupted, the FPGA may fail to initialize.

eMMC (Embedded Multi-Media Controller) Configuration

eMMC is a high-speed, non-volatile storage solution often found in mobile devices and embedded systems. While not as commonly used for FPGA programming as QSPI, it offers large storage capacity and rapid data transfers.

How eMMC Works

  • The FPGA retrieves bitstream data from an eMMC storage device.
  • The high-speed controller ensures fast and reliable configuration.
  • eMMC can store larger bitstreams, making it useful for complex FPGA designs.

Benefits

✅ Ultra-fast configuration speeds – Faster than both JTAG and QSPI.
✅ Large storage capacity – Suitable for big FPGA bitstreams.
✅ Wide industry adoption – Common in mobile and embedded applications.

Drawbacks

❌ Increased complexity – Requires additional hardware and software support.
❌ Higher cost – More expensive than QSPI and JTAG-based solutions.
❌ Less common for FPGA programming – Primarily designed for storage and bootloaders, not dedicated FPGA configuration.

Choosing the Right Ultrascale Configuration Method

The optimal Ultrascale FPGA configuration technique depends on several factors:

Method Speed Flexibility Non-volatile External Memory Production Suitability Cost
JTAG Slow High No No Low Low
QSPI Fast Medium Yes Yes (QSPI Flash) High Medium
eMMC Very Fast Low Yes Yes (eMMC Chip) High High
  • For debugging and development, JTAG provides fine-grained control but is slow and not ideal for production.
  • For production deployments, QSPI is a fast, compact, and reliable choice, commonly used in modern FPGA designs.
  • For high-speed applications, eMMC offers maximum efficiency and storage but comes with higher complexity and cost.

Often, engineers combine JTAG for debugging with QSPI or eMMC for production, leveraging the strengths of both methods.

Final Thoughts

Understanding FPGA programming modes is crucial for optimizing configuration speed, reliability, and cost-efficiency. Whether you’re developing new designs, troubleshooting configuration issues, or deploying FPGA-based systems, selecting the right configuration method ensures smooth operation and maximum performance.