Raptor Computing Systems Community Forums (BETA)

Water Cooler => General OpenPOWER Discussion => Topic started by: pocock on September 14, 2022, 11:34:52 am

Title: external oscillator in v1.01 boards - which problems does it aim to resolve?
Post by: pocock on September 14, 2022, 11:34:52 am

The wiki mentions that newer boards (v1.01) have an external oscillator for the FPGA (https://wiki.raptorcs.com/wiki/Updating_Firmware#Troubleshooting)

The oscillator is mentioned in this commit (https://git.raptorcs.com/git/talos-system-fpga/commit/?id=df7e808365f0cbb8175f7f634dc9bc7a3e3a7443)

If somebody has an older FPGA, e.g. 1.06 and they have a v1.01 motherboard, is there a pressing reason to upgrade the FPGA to 1.08?

Are there any particular problems that might occur if the user does not upgrade?

Title: Re: external oscillator in v1.01 boards - which problems does it aim to resolve?
Post by: AdamJoseph on September 25, 2022, 04:10:32 pm

Quote from: pocock on September 14, 2022, 11:34:52 am

The oscillator is mentioned in this commit (https://git.raptorcs.com/git/talos-system-fpga/commit/?id=df7e808365f0cbb8175f7f634dc9bc7a3e3a7443)

From that commit:

<pre>
-   // Implement nasty ring oscillator for fallback use when main system clock is offline
-   // Thanks to Clifford Wolf for the idea and basic code!
</pre>

Wow, I'm surprised they have to use a LUT-based ring oscillator here.  All the Xilinx and Altera FPGAs I've ever dealt with had an internal "hard" (not made of LUTs) ring oscillator that could be routed into the fabric.  Still not great, but more predictable than LUTs.  Don't the Lattice ICE chips have this?  Can't the PLLs be used for this (use the slowest setting, ignore the lock signal)?

Anyways, if your board has the external oscillator you should definitely use it.