Am Sun, 26 Mar 2017 18:51:38 +0200 hat "H. Nikolaus Schaller" hns@goldelico.com geschrieben:
Hi,
This obviously means as conjectured that the eMMC has severe problems at HS200 speed and there is no mechanism to fall back to slower speeds.
After reducing DT speed to
max-frequency = <92000000>;
the CRC errors are gone.
Well, that's probably because of the MUX, which will not be able to run at HS200.
Next I tried 142MHz and it also works w/o any CRC error and is faster: root@letux:~# hdparm -tT /dev/mmcblk0
/dev/mmcblk0: Timing cached reads: 992 MB in 2.00 seconds = 495.98 MB/sec Timing buffered disk reads: 244 MB in 3.02 seconds = 80.85 MB/sec root@letux:~# hdparm -tT --direct /dev/mmcblk0
Interesting. If I understood correctly, the MUX doesn't support more than 120MHz (or 60MHz, depending whether you run in SDR or DDR)
So that would be quite some overclocking, or not?
The strange thing is that increasing the max-frequency by 50% gives double speed... Maybe someone else can extend experiments based on this to determine the clock limit.
I'm not sure that the frequencies are freely supported. Maybe the eMMC has some fixed frequencies it'll run with and therefore runs lower when clocked with 92MHz...?
No idea :)