问题
I am having a problem with the I2C driver for a Freescale p1022tw board. There is a command on U-Boot's console to read from an I2C device:
i2c md chip address[.0, .1, .2] [# of objects]
When I read 4 bytes from a device with id 0x60, at address 0x0, I get:
tw=>i2c md 60 0 4
0000: 45 45 45 45 EEEE
These values that it returned are wrong. I can get the right values if I read one byte at the time:
tw=>i2c md 60 0 1
0000: 45 E
tw=>i2c md 60 1 1
0001: 45 E
tw=>i2c md 60 2 1
0002: 46 F
tw=>i2c md 60 3 1
0003: 00 .
I should have gotten 45 45 46 00 or EEF0 in the first command. In multiple readings for this device, it is returning always just the first byte value. If I try to get 6 bytes starting at address 0x2, this is the output:
tw=>i2c md 60 2 6
0002: 46 46 46 46 46 46 FFFFFF
This problem does not happen on other devices on the bus. For instance, in the device with id 0x4F, the right values are printed:
tw=>i2c md 4F 0.2 6
0000: 18 00 f6 48 00 00 ...H..
The address in the previous command has a ".2" because the chip uses 2 bytes for addresses. The first device only uses 1, so there's no need to put a ".1" (I already tested that).
I went through the implementation of the Freescale driver for the I2C communication, but I didn't change anything on it and it works for other devices. My coworker also says that the very same code works on his board. Have anybody had a similar issue or has any theory about why this is happening?
Thanks in advance.
回答1:
I met such a situation. I had driver, read and write functions, and it worked not for all i2c devices. I found that was caused the not working device had different operating format for a number of operation. Unfortunately this happens, there a kind of not standard protocols. When you open the doc for the problem device and compare it to working and/or to the driver implementation you most likely will see a difference.
来源：https://stackoverflow.com/questions/24966553/reading-multiple-bytes-using-i2c-in-u-boot