The loader provides a simple interface that lets the Expansion Card manager access the card's code space. The register usage is common to the 4 entry points.
=> R0 user data, or byte to read/write
R1 user data, or address
R2 user data
R11 combined hardware address
R13 FD stack
<= R2,R3,R10 may be corrupted
Entry points:
Offset Code
0 Read a byte
4 Write a byte
8 Reset card
12 Podule_CallLoader
16 "32OK" (magic word indicating the loader can be run on a 32 bit system)
As the loader is (and has always been) entered with V clear the simplest non-error exit is MOV pc,lr.
This is contrary to the RISC OS 3 PRM which recommends a BICS pc,lr,#V_bit, which then renders the loader only suitable for use on old systems where the ARM is running in 26 bit mode.
Exit with V set and an error in R0 if you wish to return an error, but to save space in the loader ROM an error pointer of 0 will generate a default error.
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