Hi Andreas,
As far as I know, the SD library for the Galileo is meant to work only with the built-in microSD card reader on Galileo board. There are a few reasons for this:
- The microSD reader lines are independent from the SPI/CS lines on the Galileo so when you manipulate the SD library, you won't see any thing on the ICPS/SPI lines
- Intel has modified the SD library for the Galileo to specifically use the Galileo's built-in microSD reader
If you want to use a separate Arduino compatible SD card reader, you'll need to write your own library for it. Also, be aware that there are some sever timing limitations with regards to the Galileo SPI data transfer. This is primarily caused by two things:
- Each time you cycle the SPI CS, you will take a 1-10 ms delay hit, depending on whether you use fast GPIO or not
- You can hold down the CS and transfer only up to 4096 bytes at a time so each time you send another 4096 bytes via the SPI, you will take small delay hit
The above limitations of the SPI library for the Galileo board plus the fact that you need to write your own library makes it very undesirable to use an external SD shield.