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- 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 AMCC 4xx BUG!!!
- This reset edge condition could possibly be present in every I2C
- controller and device available. For boards where a I2C bus reset
- function can be implemented a i2c_init_board() function should be
- provided and enabled by #define'ing CFG_I2C_INIT_BOARD in your
- board's config file. Note that this is NOT necessary when using the
- bit-banging I2C driver (common/soft_i2c.c) as this already includes
- the I2C bus reset sequence.
- 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)
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