leandrof/u-boot
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Initial revision

Browse Source
This commit is contained in:
wdenk 2002-03-08 23:25:32 +00:00
parent ae6448002a
commit 6fcc18e0a9
1 changed files with 41 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
doc/I2C_Edge_Conditions Normal file
View File

@ -0,0 +1,41 @@
I2C Edge Conditions:
====================
I2C devices may be left in a write state if a read was occuring
and the CPU was reset. This may result in EEPROM data corruption.
The edge condition is as follows:
1) A read operation begins.
2) I2C controller issues a start command.
3) The I2C writes the device address.
4) The CPU is reset at this point.
Once the CPU reinitializes and the read is tried again:
1) The I2C controller issues a start command.
2) The I2C controller writes the device address.
3) The I2C controller writes the offset.
The EEPROM sees:
1) START
2) device address
3) START "this start is ignored by most EEPROMs"
4) device address "EEPROM interprets this as offset"
5) Offset in device, "EEPROM interprets this as data to write"
The device will interpret this sequence as a WRITE command and
write rubbish into itself, i.e. the "offset" will be interpreted
as data to be written in location "device address".
Notes
-----
!!!THIS IS AN UNDOCUMENTED I2C BUS BUG, NOT A IBM 4xx BUG!!!
This reset edge condition could possibly be present in every I2C
controller and device available. We should probably have a bus reset
function for all our target CPUs.
Many thanks to Bill Hunter for finding this serious BUG.
email to: <williamhunter@attbi.com>
Erik Theisen <etheisen@mindspring.com>
Tue, 5 Mar 2002 23:02:19 -0500 (Wed 05:02 MET)