U-boot also offers a way of accessing, checking, reading and writing to devices via the I2C bus. With the command i2c -help all available commands and the corresponding syntax is shown. The Cosmos XZQ10 is used for showcasing the usage of some of these commands. The RTC present on the board is read with the help of the U-boot I2C tools. The command i2c bus lists all available I2C buses.
Zynq > i2c bus
Bus 0: zynq_0
With i2c probe all valid I2C addresses are listed. The device tree entry specifies the address of the RTC on the Cosmos XZQ10 as 0x6f which corresponds to the serial console output.
Zynq > i2c probe
Valid chip addresses: 0D 20 23 2F 30 32 34 36 56 57 64 6F 70 74
As an example of how to read the first six registers of the RTC the following command is used: i2c md 0x6f 0x00 0x06. The address is given as 0x6f to read from the RTC, the start address for the read is 0x00 and 0x06 is the number of registers that are read (six in this case, corresponding to seconds, minutes, hours, day, month, year).
Zynq > i2c md 0x6f 0x00 0x06
0000: 34 57 97 05 02 20 4W...
The next chapter of this application note is Chapter 5 - Linux.