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author | fishsoupisgood <github@madingley.org> | 2019-04-29 01:17:54 +0100 |
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committer | fishsoupisgood <github@madingley.org> | 2019-05-27 03:43:43 +0100 |
commit | 3f2546b2ef55b661fd8dd69682b38992225e86f6 (patch) | |
tree | 65ca85f13617aee1dce474596800950f266a456c /roms/u-boot/doc/I2C_Edge_Conditions | |
download | qemu-master.tar.gz qemu-master.tar.bz2 qemu-master.zip |
Diffstat (limited to 'roms/u-boot/doc/I2C_Edge_Conditions')
-rw-r--r-- | roms/u-boot/doc/I2C_Edge_Conditions | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/roms/u-boot/doc/I2C_Edge_Conditions b/roms/u-boot/doc/I2C_Edge_Conditions new file mode 100644 index 00000000..f4a99687 --- /dev/null +++ b/roms/u-boot/doc/I2C_Edge_Conditions @@ -0,0 +1,46 @@ +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 CONFIG_SYS_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) |