[sdiy] a provoking question about time

Dave Brown davebr at modularsynthesis.com
Sun Jun 26 21:19:04 CEST 2022


I don’t remember the retention for 2708 eproms, but I thought it was something like 10 years. In 1976 I built a musical doorbell using an 8080/2708. It was modelled after the music program that ran on a Sol-20. I could create new songs and upload them to my doorbell. While I can no longer do that, it does still play the default music selection. It’s been running continuously now for 46 years. I’ve only had to do two repairs on it. One was the capacitor in the -5V converter went bad. The other is the 8080 died. The 2708 is still running with the original program. It has sat in a tight loop waiting for someone to press the doorbell button. For the last nearly four decades I’ve lived remotely so it doesn’t get pressed but maybe 2/month. I calculated once how many loops that processor has gone through but I forget now. I know this isn’t related to the flash memory, but it’s a testament to the retention of at least this 2708.


Dave

 

From: Synth-diy <synth-diy-bounces at synth-diy.org> On Behalf Of ASSI
Sent: Sunday, June 26, 2022 11:27 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] a provoking question about time

 

On Donnerstag, 23. Juni 2022 11:34:04 CEST Roman Sowa wrote: > what are your concerns about flash retention time in microcontrollers? There's usually something else in the system that will fail years 

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On Donnerstag, 23. Juni 2022 11:34:04 CEST Roman Sowa wrote:

> what are your concerns about flash retention time in microcontrollers?

 

There's usually something else in the system that will fail years before that 

happens…

 

> Usually PIC18 and PIC16 claim 40 years in datasheet, but dsPIC only 20.

> I've seen corrupted memory in products made about 15 years ago with

> dsPIC, so datasheet value seems real.

 

If it wasn't programmed with their "professional" programmer, the datasheet 

values are void and even then there are other failure modes that affect memory 

integrity that produce similar lifetime / failure rate profiles.

 

> One way to do it is to rewrite all memory from time to time, but how to

> do that? Even if there's real time clock running, the user may always

> change the date, and if it's not alowed, the battery or supercapacitor

> may die, or get ripped away. My idea is to clearly state somewhere, in

> manual, or on the device "please run maintenance procedure if it's year

> ending with 0 or 5" but I'm affraid nobody will do that anyway, and it

> seems foolish.

 

If you are thinking of overwriting a Flash block with the same data (no 

erase), all you're gonna do is to slowly destroy the data via program disturb 

(which is also data-dependent).  Flash is meant to be erased by blocks and 

programmed by word-lines, each cell just once per cycle.

 

If the Flash in question offers a margin read operation: use that after 

programming to weed out parts that did not program well or had latent defects.  

You can sometimes do that even during normal operation (say on boot), i.e. 

compare a normal and a margin read to get early warning of impending data 

loss.

 

 

Regards,

Achim.

-- 

+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

 

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