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The DRAM controller allows to configure impedance either by using the calibration against an external high precision 240 ohm resistor, or by skipping the calibration and loading pre-defined data. The DRAM controller register guide is available here: http://linux-sunxi.org/A10_DRAM_Controller_Register_Guide#SDR_ZQCR0 The new code supports both of the impedance configuration modes: - If the higher bits of the 'zq' parameter in the 'dram_para' struct are zero, then the lowest 8 bits are used as the ZPROG value, where two divisors encoded in lower and higher 4 bits. One divisor is used for calibrating the termination impedance, and another is used for the output impedance. - If bits 27:8 in the 'zq' parameters are non-zero, then they are used as the pre-defined ZDATA value instead of performing the ZQ calibration. Two lowest bits in the 'odt_en' parameter enable ODT for the DQ and DQS lines individually. Enabling ODT for both DQ and DQS means that the 'odt_en' parameter needs to be set to 3. Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com> Acked-by: Ian Campbell <ijc@hellion.org.uk> Signed-off-by: Hans de Goede <hdegoede@redhat.com> |
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