[A83] Re: What is the problem with flash writes (in general)

To: <assembly-83@lists.ticalc.org>
Subject: [A83] Re: What is the problem with flash writes (in general)
From: "Dan Englender" <dan@calc.org>
Date: Mon, 9 Jul 2001 15:07:03 -0400
References: <200107091855.f69ItZR18178@sunsparc.hysoft-automation.com>
Reply-To: assembly-83@lists.ticalc.org


Slightly more in-depth explanation:
The ability to write to the Flash is tied directly to port 14h.  Output a
one to that port, flash access is enabled (allowing writes, erases, and
reads from protected sectors).  Output a zero, and it's locked again.
The little detail is that the hardware only listens to outputs from port 14h
if the code is coming from page 1Ch, 1Dh, or 1Fh (7Ch,7Dh, or 7Fh on the SE)
.  You can look at the code for yourself, but TI does a pretty good job of
making sure you can't call a routine that would leave the Flash unlocked.
They also check for all sorts of trickeries like loading ROM pages into port
7, interrupts, etc.

-Dan Englender

----- Original Message -----
From: "Hyperbyte" <hyper@hysoft-automation.com>
To: <assembly-83@lists.ticalc.org>
Sent: Monday, July 09, 2001 2:55 PM
Subject: [A83] Re: What is the problem with flash writes (in general)


>
> Simply put, no user-program can do it.
>
> Explanation:
> The flash chip has a "write enabled" line,
> only if this line has specific signal, one can write to the flash
>
> Now one could simply set this signal, if TI hadn't prevented that,
> they've somehow made it only possible for certain OS Rompages to
> set that value.
>
> (I think it's kinda obsolete now, since TI's released the app signing key,
> but I doubt they'll insert _FlashWE and _FlashWD romcalls in new OS'es)
>
> You could hardware hack that WE line, but then your program wouldn't be
distributable...
>
> --(Peter-Martijn)
>
>
> > Not really that no one has been able to do them in their programs, but
the
> > fear of failure.
> >
> > "Minimum 1,000,000 program/erase cycles per sector
guarantead" -Am29F400B.pdf
> > (amd's tech doc on it)
> >
> > Writing to it for everything, would be a hazard, but having programs do
> > write-back to the flash for storage, shouldn't hurt at all. (if we could
do
> > it)
> >
> >
> > Just my .02USD
> > James L.
> >
> >
>
>
>

References:

[A83] Re: What is the problem with flash writes (in general)

From: Hyperbyte <hyper@hysoft-automation.com>