64-bit values on 32-bit machine

[Harald Krapfenbauer <krapfenbauer@ict.tuwien.ac.at>]

Hello,

I want to know how 64-bit values are passed on a little-endian 32-bit
MIPS machine on function calls.

If there is one 64-bit argument to a function, it is passed in registers
a0-a1 I think, but does a0 contain the lower 4 bytes or the upper 4?

Similarly, if there are several arguments so that a 64-bit argument is
passed on the stack: Do the lower 4 bytes go to the lower address or to
the higher?

Thanks in advance!
Harald