Introducing Kestrel

The new product tease we reported on from Raptor has a name: Kestrel. We theorized it was a FlexVer peripheral, but Raptor says it isn't, though it says "it's one of the most critical components of one." The image posted on Twitter (reproduced here) requires connection to the LPC, I2C (both platform control and AVSBus) and FSI signals, the latter of which will require either soldering or voltage conversion. Seems a strange omission for why that wouldn't simply be included on the board. Another curious omission is that the image also adds it has not yet been tested on the flagship Talos II (or presumably the T2 Lite), just the Blackbird, though reading the little what's available I don't see why it wouldn't work.

So, after all that, what does it do? The connection to those buses suggests some sort of low-level system monitor. If you really want to get down to the lowest level of what your system is executing, this is probably the device you want on one of the few systems that lets you do it as a supported feature. Here's a schematic of what the POWER9 is doing on bootup (what IBM docs call IPL, or the Initial Program Load):

The FSI connection is the biggest key here, which is the OpenPOWER Flexible Support Interface. This interface is active very early in standby mode, with clock signals available shortly after the machine is connected to power and the BMC is coming up — before even "Step 0" on this flowchart. Among many other things, the FSI triggers when the POWER9 Self-Boot Engine starts executing from its fused-in OTPROM, which contains the first instructions the POWER9 executes, and the BMC uses the FSI to determine which side of the SEEPROM the main CPUs should boot from. The FSI and IPC connections also allow monitoring the PNOR and other low-level traffic. With all these busses running through the Kestrel, you should be able follow the BMC and main CPUs all the way from standby to the end of IPL.

What we still don't know is if it will let you actually manipulate these signals, which could be a very powerful tool. Yes, you could potentially wreak havoc on your machine but I think soldering connections wrong would have a similar effect, so why not give us the keys to the store? Even if it's merely as a monitor, however, it could certainly be a way to have confidence a machine has not been tampered with and for hardware designers to understand better how present-day OpenPOWER systems operate.