Sometimes I want program to jump to uncertain (run-time determined) address like function pointer does in C language. For example, a function table. If the chip supports "jsr" with register indirect addressing, like H8, it will be as simple as
jsr @er0
But on the core I am using called "Flex RISC", 8bit, performs as peripheral device in an ARM based SoC, thers is only one "jsr" instruction which using immediate addressing. Branch instructions (brXX) and jmp instruction do the same.
At last I found there is another instruction changes PC pointer, "rts". It pop PC point from stack. So here is the way out:
...
; variable SomeAddr keeps SomeFunc's sddress
ld a1, SomeAddr
ld a2, SomeAddr + 1
jsr CallByAddr
...
SomeFunc:
...
rts ; this "rts" will exactly returns from the "jsr".
CallByAddr:
psh a2
psh a1
rts ; this "rts" will pop a2a1 to PC that makes SomeFunc called.
jsr @er0
But on the core I am using called "Flex RISC", 8bit, performs as peripheral device in an ARM based SoC, thers is only one "jsr" instruction which using immediate addressing. Branch instructions (brXX) and jmp instruction do the same.
At last I found there is another instruction changes PC pointer, "rts". It pop PC point from stack. So here is the way out:
...
; variable SomeAddr keeps SomeFunc's sddress
ld a1, SomeAddr
ld a2, SomeAddr + 1
jsr CallByAddr
...
SomeFunc:
...
rts ; this "rts" will exactly returns from the "jsr".
CallByAddr:
psh a2
psh a1
rts ; this "rts" will pop a2a1 to PC that makes SomeFunc called.
