I am have written a driver for my sound card

1. If I palce the driver in SDCard and launch the IO-Audio with -d option to specify driver path it does not use this 
driver instead it uses default driver present in other folder.
2. If I place the driver in tmp folder & launch the IO-Audio with -d option to specify driver path it uses this driver.

I would like to know why option 1 does not work ...