Is there an example of how to perform DDR data bit swapping as described in AN5122?

[damien1]

We are using LPDDR2 and have wired the data bits as per the ST provided example STM32MP15XXAD_LPDDR2x16-Example-A01_Schematic.PDF (attached)

We have swapped the same bits in the DQ15:8 byte as per the PDF but I can't find anything to tell me how to perform this swapping in the devicetree or otherwise.

Below is the screenshot from the Application Note detailing that bit swapping is possible.

[PatrickF · Accepted solution]

Hi @damien1​ ,

on a pure RAM, no matter the data bus swapping (bits within a byte or bytes Vs bytes), your read what your have written. So, no need to configure any HW/SW about this.

Obviously, in case of bytes swap, DQS/DQM should follow their byte.

There is anyway some restriction on byte and but swapping (e.g. D0-D7 on LPDDR2/3 should be on byte0 without any bit swap) as data bus could also carry access to memory internal config/status registers.

On DDR3/DDR3L, all data swaps are allowed because writting memory register is done using address bus as data (which is not the case on LPDDR).

Regards,

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