Re: RP2040 reset idea

On Tue, 17 Sep 2024 11:07:17 +0100, The Natural Philosopher
<tnp@invalid.invalid> wrote:

On 17/09/2024 03:58, john larkin wrote:

The RP2040 has a cool mode where it can be made to boot up with the
USB port looking like a memory stick. That's great for software
installs or upgrades. The Pico board has a BOOT button on the board;
if the pico is powered up with the button pushed, it goes into that
boot mode.
 
But if I have a product (actually a family of products) in a nice
aluminum box, a user would have to remove the top cover, remove all
power sources (there can be three), and hold the button down while
reconnecting power.
 
Some of my customers also want to lock a box such that it's impossible
to write to any nonvolatile memory while it's in a secure area.
 
So here's an idea: a small hole in the box allows a toothpick or a
paper clip to push a button. A short push is a regular reset. A long
push is a memory-stick mode boot. We can have a rotary switch LOCK
hole too.
 

Thats' what my PICO powered thermostats have. For the onboard button though
Resetting is done by pulling the power.
>
The point is that if you do power up with the button pressed, you wipe
the entire FLASH RAM I think.

If BOOT- is low at the end of reset, it powers up in USB memory stick
mode. I don't think that wipes the files stored in the big serial
flash.

>
>

https://www.dropbox.com/scl/fi/bbhdy053xsdzv77g0brc5/B-box_Reset_Button_3.jpg?rlkey=40ozzdvczf4z8625u8i081a9b&raw=1
 
Does that look like it will work? The paranoid customer can pave over
the two holes, and even the end-plate screws, with an official-looking
sticker.

At a brief glance, yes, but I donbt see why a simmle disconnect power
switch in addition to the onboard switch wouldn't be as easy.

There are three potential power sources to disconnect, and I don't
really want a power switch.

 
Schmitt trigger U3 is unfortunate and likely unnecessary, but it
insures against a low-probability hazard.
 

Once you start laying out a board, put everything on it you may need,
Can always leave it out later

The schmitt adds way under a tenth of a per cent to the board area and
the cost, so may as well leave it in.