On 2016/5/11 11:50, Doug Anderson wrote:
Hi,
On Tue, May 10, 2016 at 7:50 PM, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
maybe. But I think 180(downside) is the better.
NAK my previous comments here. Downside is better for SRD, but won't
work for DDR mode. When running in DDR mode, we should use 90 instead.
So let me elaborate a bit more here.
For DDR mode, one single clk cycle should sending two data bits outside
to the devices. We need a hold time for both. If 180 is used, the first
bit occurs around the downside area, which won't be sampled by devices
on the upside. So on the upside, the devices will see a zero bit if you
actually send a one-bit, which makes the devices generate CRC finally.
For this above, 180 for all SDR mode is ok, but 90 should be deployed
for DDR mode. So simply checking the timing to hardcode it should be
fine.
OK, I sent out a patch for 180 always. I can send v2 to use 90 for
DDR modes tomorrow. ...or feel free to post that yourself if you
want.
We want 90 for all DDR modes? So MMC_TIMING_UHS_DDR50,
MMC_TIMING_MMC_DDR52, MMC_TIMING_MMC_HS400? (not that we support HS400
in dw_mmc on Rockchip).
Right.
-Doug
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Best Regards
Shawn Lin
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