I/O Pad Clock Domain

[Kathleen Feng]

Hello,

I am taping out a Chipyard design and have technology-specific I/O pads in my design. Their max frequency is much less than that of the rest of the design, and I want to put the I/O pads in a separate clock domain. After reading through previous posts, it seems like the TL serial link/JTAG have their own clocks and are asynchronous from the rest of the system.

Is this a correct interpretation? Does Chipyard already handle the clock domain crossings between the interface pads and the rest of the system? If not, is there an example of how to add this?

Thanks,

Kathleen

[Jerry Zhao]

> Is this a correct interpretation? Does Chipyard already handle the clock domain crossings between the interface pads and the rest of the system? If not, is there an example of how to add this?

Yeah this is right. JTAG provides its own clock externally via jtag.TCK, so you just have to limit that to what your pads can handle.
The only concerning signal is serial-TL, as you've mentioned. The default ChipLikeRocketConfig in upstream chipyard synchronizes the sertl lanes to the externally driven sertl clock, with an internal crossing to the rest of the digital side.

If you are doing a tapeout with Chipyard, you should look at the configs in ChipConfigs.scala. The ChipLikeRocketConfig is the closest "tapeout-ready" configuration. The ChipBringupHostConfig is a config of the FPGA-side bringup system. The TetheredChipLikeRocketConfig simulates the chip alongside the FPGA bringup harness, enabling early-stage RTL simulation of the entire bringup procedure.

-Jerry

--
You received this message because you are subscribed to the Google Groups "Chipyard" group.
To unsubscribe from this group and stop receiving emails from it, send an email to chipyard+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/chipyard/80d4bdcc-9ec7-4b3b-adc0-21c0c72bc7a8n%40googlegroups.com.

[Kathleen Feng]

Hi Jerry,

Great, thank you for the response and the pointers to existing configs!

Kathleen

You received this message because you are subscribed to a topic in the Google Groups "Chipyard" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/chipyard/eKHPG2S33Mc/unsubscribe.
To unsubscribe from this group and all its topics, send an email to chipyard+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/chipyard/CAC%2BpDSHSRf1KTdg_7CgKFgLQrMk01YiOjs_DN_uU16mvU794_Q%40mail.gmail.com.