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diff --git a/doc/I2C_Edge_Conditions b/doc/I2C_Edge_Conditions new file mode 100644 index 00000000000..91557a3ca97 --- /dev/null +++ b/doc/I2C_Edge_Conditions @@ -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) |