SAMA5D27 SOM1 SDHC/eMMC Write Speeds

[jwoodward]

Hello,

I have tested both a micro sdhc and an eMMC with the SAMA5D27 SOM1 SK and on my PC.
Both memory modules on PC write at a rate of 20 MB/s or more however on the SAMA5D27 SOM1 SK only 4 to 5 MB/s.

I would be interested to know what the limiting factors could be? CPU? Sharing SPI line with NAND flash?

I've also noticed the CLK speed on the MMC connector is varying between 4MHz and 10MHz, is this normal?