When an XC7K325T-1FFG900C board fails to start or loses data intermittently, preserve the failure evidence before changing the design. A useful fault record identifies the board revision, full FPGA marking, power source, bitstream hash, constraints and reproduction steps. The workflow below separates power, configuration, clocks, logic and external links so that a successful test in one area is not mistaken for proof of the entire board.
Start with a symptom and a discriminating test
| JTAG device absent | Measure board rails and cable reference voltage; inspect chain continuity, reset conditions and clock quality. |
|---|---|
| JTAG works, flash boot fails | Compare a direct JTAG load with the intended boot mode; capture configuration pins and inspect the flash image layout. |
| DONE is high, application silent | Check application reset, clock enables and a simple observable counter before adding the full data path. |
| Serial link fails | Confirm exact line rate, reference clock, reset sequence and lane mapping; isolate internal from external loopback tests. |
| Failure under sustained traffic | Log FIFO occupancy, overflow flags, DMA completion and temperature while holding the stimulus constant. |
Change one variable per experiment and save the result, including unsuccessful tests. The purpose is to narrow the fault domain; replacing several regulators, changing the image and lowering the interface rate together may restore operation without explaining why it failed.
Power-up measurements should match the actual rail rules
DS182 recommends VCCINT, VCCBRAM, VCCAUX, VCCAUX_IO and VCCO sequencing, with documented allowances for rails at the same voltage to ramp together. It provides separate GTX supply sequencing guidance. A blanket statement that every simultaneous ramp damages the FPGA is incorrect. AMD DS182: Kintex-7 DC and AC Switching Characteristics.
Capture all relevant rails against time during cold start and during a short power interruption. Measure at accessible load-side points using a suitable probing method. Check ramp shape, overshoot, regulator current limiting and the point at which configuration begins. A static multimeter reading cannot reveal a brief excursion that occurs only when the logic starts switching.
Make a rail-by-rail limit sheet rather than applying one percentage tolerance to every supply. Record nominal voltage, allowed range, startup dependency, measured minimum and maximum, and the acquisition bandwidth. When testing GTX failures, include its analog rails and reference-clock supply environment; a clean core rail alone does not clear the serial interface.
Separate configuration success from design correctness
Use configuration status and the documented startup behavior in AMD UG470: 7 Series FPGA Configuration. First attempt a small, known build through JTAG using the correct device target. If that works while autonomous boot fails, compare boot-mode wiring, flash contents and configuration-clock settings before modifying the application logic.
DONE indicates a stage of configuration; it does not establish that every user clock is present, resets release safely, or the application meets timing. Likewise, the device identification code is not a certificate that the speed-grade assumptions in the implementation match the installed part. Inspect the project target and retained implementation reports directly.
For a flash update failure, retain a readback or checksum of the programmed image where the programming workflow supports it. Compare the image offsets with the generated configuration-memory file. Avoid treating a larger flash capacity as proof of command or addressing compatibility. Establish a recovery procedure before intentionally testing interrupted updates.
Find the first clock or reset boundary that stops progressing
Use small counters or status flags at successive points: input clock domain, clock-management output, reset release, interface training and application state machine. Sample a changing status across domains with a deliberate synchronization or handshake scheme. An instrument clocked by a missing clock cannot reveal that clock’s absence; observe a divided heartbeat from an independent measurement point when appropriate.
Review clocks, generated clocks, I/O timing and clock-domain crossings against the intended architecture. Do not silence an unexpected timing failure with a broad false-path exception. An asynchronous control input needs an appropriate synchronization design; a synchronous external interface needs constraints derived from the external device and board timing. These are different cases.
Save the failing timing path and its clock relationship, then verify that a correction changes the intended path. Run the same test after reset and clock-source changes. A design that works after a warm reconfiguration may still have an untested cold-start dependency.
GTX tests: qualify the test boundary
The exact -1 FFG900 rate ceiling is 8.0 Gb/s, with the DS182 four-byte internal-width requirement above 5.0 Gb/s. AMD DS182: Kintex-7 DC and AC Switching Characteristics. Confirm the generated transceiver configuration before investigating a channel at a family headline rate the installed device does not support.
Internal loopback can help isolate part of the data path, but it does not exercise every connector, cable or remote receiver. External loopback adds some of those elements, while a full peer-to-peer test also covers interoperability and independent clocks. Label test results with the loopback mode, pattern, line rate, lane count, equalization configuration and elapsed error-free bits.
For an illustrative statistical check, a 5 Gb/s test running for 60 seconds observes 300 billion bits. With zero errors, the approximate 95% upper confidence bound under an independent-error model is 3/N, or 1 × 10−11. This is not proof of zero error rate, and the model does not capture every burst-error mechanism. Longer runs and operating-corner tests answer different questions from a short bench check.
Traffic and temperature faults need correlated logs
Log FIFO high-water marks, dropped-frame counters and host backpressure alongside the symptom timestamp. If stopping the input prevents failure, determine whether the recovery comes from reduced bandwidth demand, lower switching activity or a reset side effect. Keep input rate and data pattern controlled during the comparison.
Estimate and measure the thermal behavior of the assembled board. Commercial temperature limits refer to junction temperature; ambient readings alone cannot establish margin. Do not assume the FPGA automatically throttles a user-designed data path. If thermal protection is required, define the monitoring, decision logic and safe system response explicitly.
An escalation package should include the schematic fragment, rail captures, clock source and frequency, configuration status, timing summary and the shortest reproducer. Remove unsupported conclusions such as “counterfeit” based only on a current reading. For exact resource limits see the XC7K325T-1FFG900C specification guide; for buffer sizing see the DAQ design example.
Ordering and references
For an XC7K325T-1FFG900C quotation, send the complete code, quantity, required delivery date and documentation requirements through the WWDParts RFQ list. Availability, price and delivery terms are confirmed in the written quotation. A different package, temperature grade or speed grade requires a design review before substitution.
Technical content reviewed October 13, 2026. Worked examples are design calculations with stated assumptions, not measurements or hardware qualification results.