Seeed Xadow M0 working with SD card add-on

Dependencies:   SDFileSystem SSD1308_128x64_I2C USBDevice mbed

Fork of SDFileSystem_HelloWorld by mbed official

Revision:
1:4ac234866e4c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/USBDevice.lib	Fri Nov 21 13:15:45 2014 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/yihui/code/USBDevice/#74ca09725b68