[U-Boot] Load a kernel image

[Ivan Llopard]

Hi list,
I'm working with an embeded system. I'm sure you know about the
microprocessor NIOS2. I have chose u-boot and it runs perfectly in
my platform. But it can't read my memory SD card how i have it
configured. I would like to know how to load the kernel image (uclinux) in
memory correctly by myself, i mean without u-boot, or where i can find
some information about it. I got the image of kernel uclinux in elf
format and i get errors with gzip magic numbers when i try to load my
image at his linked address.
I would like also to develop a SPI driver for u-boot in order to read
SD cards memory, i don't know if it's already developed.
Regards,
Iván.