Good question... Maybe it was just during development you need to disable it in order to successfully flash new code since nothing would be resetting the wd? I know on my board, the jumper is always in place so I don't know that we've tested the hw wd.

Btw, the tms570 has a software watchdog which we have code for and we have tested.

I also vaguely recall a conversation about the timing of the hw wd. I don't remember if it was the wd on the 1.1 board or the 1.2 board, but Zach had proposed a chip with a maximum timeout of something pretty short - well under a second. I was concerned that if something went south, the wd chip would continuously power cycle the processor multiple times a second.

These conversations were from a while ago and I likely have the details wrong.

On Fri, Jan 20, 2023, 8:18 AM Jonathan Brandenburg via pacsat-dev <pacsat-dev@amsat.org> wrote:

This I didn't know! Does anybody on the list know why the hardware watchdog wasn't working as expected on the RT-IHU?

Jonathan

On 1/19/23 17:43, Rich Gopstein wrote:

And - as long as I'm thinking about it, we had to disable the hardware watchdog on the RT-IHU to get it to run. I don't recall if that changed, but if you get some RT-IHU boards, you might need to jumper the hardware WD disable.

Rich

On Thu, Jan 19, 2023 at 6:40 PM Rich Gopstein via pacsat-dev <pacsat-dev@amsat.org> wrote:

Burns might remember the details (or Zach certainly would), but one of those parts was undersized for the RT-IHU and would cut out when we were transmitting with the ax5043. I think we had to back down the xmit power in order for the device not to reset.

Rich

On Thu, Jan 19, 2023 at 5:46 PM Jonathan Brandenburg via pacsat-dev <pacsat-dev@amsat.org> wrote:

In last week's meeting, I noted I had been looking at the schematics for
Fox-1 and RT-IHU and found the circuits for the latchup protection and
watchdog functions. I admit this might be basic to some, but I'm finding
it fascinating! Anyway...

Since last week's meeting, I researched the parts used:

onsemi FPF2001 is a current limit switch used on both Fox-1 and half the
RT-IHU. It's obsolete, replaced by onsemi's FPF2000. But the FPF2000 is
listed as end-of-life. It's replacement part is the TI TPS22942.

MAX4995 is a current limit switch used on the other half of the. This
part looks good for new designs.

For the watchdog functionality, both Fox-1 and RT-IHU use the
STWD100NYWY3F chip. this parts looks good for new designs.

That's as far as I got. Next, I want to research the Fox-1 and RT-IHU
designs to determine the thresholds of the current limit switches. In
particular, I want to see if the TPS22942 is a suitable replacement,
assuming we have the same current requirements.

That's where I'm at,

Jonathan

--
Jonathan Brandenburg
Radio Amateur Satellite Corporation
1-214-213-1066

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Radio Amateur Satellite Corporation
1-214-213-1066
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