How to set DDR data bus width to 16Bit

How to set DDR data bus width to 16Bit

[Frank Prepelica]

Hi all,

Does anyone knows how to set the DDR data bus width to 16Bit in linux?
I've found that=20
option in U-Boot in the MPC8313ERDB_config file. (verfied with a memory
dump of the=20
CPU register (DDR_SDRAM_CFG)  - the 16Bit DBW is set(10b) ). But after
starting=20
linux the value is set to 00b (=3Dreseverd).

We are using a customized MPC8313ERDB board.

Thanks in advance


Kind regards

Frank Prepelica
Software Design Engineer

Ubidyne GmbH
Lise-Meitner-Str.-14
89081 Ulm - Germany

Re: How to set DDR data bus width to 16Bit

[Norbert van Bolhuis]

you have to do it via your bootloader (u-boot) which sets up
the DDR memory controller.
Linux (already) assumes memory is available.
Are you sure linux kernel is changing DDR_SDRAM_CFG ?
When our linux-2.6.28 kernel is up, it's still 0xc3080000 when I read
physical address 0xe0002110.

Btw. We did some performance tests with 16 bit bus-width (DDR2 memory)
and surprisingly performance was almost as good as 32 bit bus-width


---
N. van Bolhuis.




Frank Prepelica wrote:
> Hi all,
> 
> Does anyone knows how to set the DDR data bus width to 16Bit in linux?
> I've found that 
> option in U-Boot in the MPC8313ERDB_config file. (verfied with a memory
> dump of the 
> CPU register (DDR_SDRAM_CFG)  - the 16Bit DBW is set(10b) ). But after
> starting 
> linux the value is set to 00b (=reseverd).
> 
> We are using a customized MPC8313ERDB board.
> 
> Thanks in advance
> 
> 
> Kind regards
> 
> Frank Prepelica
> Software Design Engineer
> 
> Ubidyne GmbH
> Lise-Meitner-Str.-14
> 89081 Ulm - Germany
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