Can I use IAR embedded ARM compiler to work on the board?
Probably. Ask IAR :) :)
John
Even if it possible I believe that this is not a good idea. A20 is a chip that comes with operating system and bootloader. Using it as a general-purpose ARM chip would be a really great effort - due to lack of previous experience and lack of documentation.
Best regards,
Lub/OLIMEX
Using a low level dev suite like IAR for a complex MPU ? Yeah depends on what you wants! Some bare metal code for a low cost dsp based on neon: great! Especially because now with iar 7 up the compiler vectorise for you the float 32 in a 4 lenght vector with a A20 MPU we can have a fast dsp at very low cost! (I agree limited to sp float32 format).
But as LubOlimex says don't even try using iar to dev on embeded linux, if there is a port for A20 in iar, iar will run it's init script to attach the target and you will get back to bare metal as fast as the speed of your probe.
Consider that uboot is effectively bare metal software, and all the data on linux-sunxi.org tells you much about how the chip etc work, so you could quite easily use normal Linux tools.
IAR may be harder...
John