Re: [Flashforth-devel] UNO lockup

[Mikael N. <mik...@fl...>]

I think the problems are  caused by corrupted eeprom contents.
It gets corrupted when reading or writing at too low Vcc.
Switching the Vcc on and off rapidly puts the chip in a state where the
eeprom is corrupted.
The prompt vector is fetched from eeprom and if it points to code
writing to flash it can also corrupt the flash.
Executing the prompt vector requires that a newline is received from the
 UART, but I guess that
could occur when playing with the Vcc. 

I did some further test with brownout disabled and added 100 ms delay in
warm
before reading or writing the eeprom. It seemed to make it more
difficult to corrupt the eeprom
but eventually it was corrupted anyway. That makes me think that when
the power is switched
off and a eeprom write occurs during a decaying Vcc, there will be
corruptions.
So a delay does not really help. 

When I add the brownout reset at 4 volts, the corruptions do not occur
anymore on my board. 

The avrasm2 ff's  have more of the code in the bootloader section and I
there may be some logical differences also, but I have not checked
further. 

One change could be to keep the prompt vector in ram only. That would
ensure it has a sane value in each startup.
You could comment out the prompt code from QUIT and see if there is a
difference. 

The difference between your boards is caused by the power supply and its
filtering characteristics. 

BR Mikael 

On 2022-03-24 02:57, Ed wrote:

> Yes - the fuse value should be 0xFC - not 0xFD as I used for my tests. 
> 
> I tried the new fuse value on FF dated 2021-11-28 but still getting flash corruption on the two boards with the SMD 328 / CH340 chips. 
> 
> While I'd like to believe those boards are faulty in some way, they seem to work fine when using FF dated 2021-03-29 or earlier. 
> 
> From: Mikael Nordman
> Sent: Thursday, 24 March 2022 06:20
> To: fla...@li...
> Subject: Re: [Flashforth-devel] UNO lockup 
> 
> I did some tests on my Arduino UNO board. 
> 
> If the brown out reset is disabled and I quickly do power on/off,  a lot of random flash and eeprom  errors occur. 
> 
> With the brown out reset enabled (any voltage), there are no errors. 
> 
> So it seems definitely recommended to have the brown detection enabled
> Probably the 4.5 V value should be the safest value. Extended fuse = 0xFC on the Atmega 328. 
> 
> BR Mikael

-- 
--
Mikael