My customer is facing the issue that DDR signals have the large overshoot and undershoot on their custom i.MX28 board.
The undershoot and the overshoot are seen on the signals that come from external DDR2.
As for the signals which flow out from i.MX28, there is no problem.
The customer thought that the issue can be improved by enabling the internal registers in i.MX28 for terminate signals by setting HW_PINCTRL_EMI_ODT_CTRL register.
And they tried the following settings, but the results were the same.
- HW_PINCTRL_EMI_ODT_CTRL = 08889999
- HW_PINCTRL_EMI_ODT_CTRL = 08888888
- HW_PINCTRL_EMI_ODT_CTRL = 0888AAAA
- HW_PINCTRL_EMI_ODT_CTRL = 08888899
They thinks that the above settings did not take effect on the impedance of the ports.
For setting the terminate register value, are there any other settings needed?