How to change RAM Data Bus width imx6?

[hishamelmeligi]

• I am trying to benchmark the effect of downsizing the RAM bus from 64 bus to 16 bits, so I used “DDRx register programming aid” file to get the dcd value for 16 bit bus width, it just changed the the DSIZ-setting in the MDCTL-register of MMDC0
  • DATA 4 0x021b0000 0x821A0000(for 64 bit bus) to DATA 4 0x021b0000 0x8218000 (for 16 bit bus)
• But after changing the bus width from 64-bits to 16-bits in the DCD, only (1/4) of the RAM is read properly in initialization function of U-Boot ;int dram_init(void) uses the function get_ram_size to validate the RAM available.
• Am I missing anything regarding this benchmark? how shall I change the bus width properly?

[igorpadykov]

Hi Hisham

in uboot please tweak ddr size in board file like:

uboot/include/configs/mx6sabresd.h

#define PHYS_SDRAM_SIZE        (1u * 1024 * 1024 * 1024)

Best regards
igor
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[hishamelmeligi]

Hi Igorpadykov

Please note that I don't want to change the RAM size, I want to change the RAM data bus width so that's why I am changing the DCD value.

The idea is that I have 4 DDR3 RAM chips sharing the 64 bit data address (each 16 bit). When I down size the data bus to 16 bit only one of the chips is accessisble and that's why I have (1/4) of my RAM size.

I was hoping that changing the bus width doesn't affect the RAM size.