SRM console callback routines

[Ivan Gaboli <Ivan Gaboli italtel it>]

Please, somebody may tell me where I can find info about SRM
console callback routine.
I've read the secondary bootstrap loader source, and in main.c there are
some call's to srm_dispatch. I'm looking for the meaning of parameters in 
the call
srm_dispatch(CCB_READ, dev, count, addr, boot_size/512 +1)
My problem is that, during the boot, with a raw bootloader, 
srm_dispatch(CCB_READ...
fails (it returns less bytes read than <count>).
Regards, Ivan