[U-Boot] MPC8541 / MPC8555E: DDR_SDRAM_CLK_CNLT[SS_EN] handling

[U-Boot] MPC8541 / MPC8555E: DDR_SDRAM_CLK_CNLT[SS_EN] handling

[Curt Brune]

Hello,

I am curious about the setting of the SS_EN bit in the
DDR_SDRAM_CLK_CNLT register:

   Source synchronous enable. This bit field must be set during
   initialization. See Section 9.6.1, ?DDR SDRAM Initialization
   Sequence,? for details.

   0 - Reserved
   1 - The address and command are sent to the DDR SDRAMs source
       synchronously.

The MPC8555E reference manual and this app note are pretty clear that
this bit should be set:

  http://cache.freescale.com/files/32bit/doc/app_note/AN2805.pdf (page 17)

set_ddr_sdram_clk_cntl() in u-boot/drivers/ddr/fsl/ctrl_regs.c has this:

        clk_adjust = popts->clk_adjust;
        ddr->ddr_sdram_clk_cntl = (clk_adjust & 0xF) << 23;

There is no accounting for the SS_EN bit on 8541/8555E.  I would have
expected to see an #ifdef for the MPC8555 that sets the SS_EN bit.

I know 8541 has been around forever and is working fine.  I am just
trying to find some back ground information on this setting.

Searching the old mailing lists did not turn up anything useful.

Any insight is appreciated.

Cheers,
Curt

[U-Boot] MPC8541 / MPC8555E: DDR_SDRAM_CLK_CNLT[SS_EN] handling

[York Sun]

You are right. We used to have this bit set for 8555 and 8541. I believe it was
removed/dropped/lost by this commit 457caecdbca3df21a93abff19eab12dbc61b7897.

York


On 02/12/2015 11:35 PM, Curt Brune wrote:
> Hello,
> 
> I am curious about the setting of the SS_EN bit in the
> DDR_SDRAM_CLK_CNLT register:
> 
>    Source synchronous enable. This bit field must be set during
>    initialization. See Section 9.6.1, ?DDR SDRAM Initialization
>    Sequence,? for details.
> 
>    0 - Reserved
>    1 - The address and command are sent to the DDR SDRAMs source
>        synchronously.
> 
> The MPC8555E reference manual and this app note are pretty clear that
> this bit should be set:
> 
>   http://cache.freescale.com/files/32bit/doc/app_note/AN2805.pdf (page 17)
> 
> set_ddr_sdram_clk_cntl() in u-boot/drivers/ddr/fsl/ctrl_regs.c has this:
> 
>         clk_adjust = popts->clk_adjust;
>         ddr->ddr_sdram_clk_cntl = (clk_adjust & 0xF) << 23;
> 
> There is no accounting for the SS_EN bit on 8541/8555E.  I would have
> expected to see an #ifdef for the MPC8555 that sets the SS_EN bit.
> 
> I know 8541 has been around forever and is working fine.  I am just
> trying to find some back ground information on this setting.
> 
> Searching the old mailing lists did not turn up anything useful.
> 
> Any insight is appreciated.
> 
> Cheers,
> Curt
>