Mark Smotherman. Last updated September 2002.
The M88K family was a 32-bit RISC design from Motorola in the 1980s. The first generation implementation consisted of the 88100 CPU and 88200 MMU. The second generation implementation was called the 88110, and several ISA changes were introduced. The M88K family was discontinued when Motorola switched over to the PowerPC. (PowerPC has both 32-bit and 64-bit programming models.)
The 88110 had 32 32-bit general registers, r0-r31, and 32 80-bit floating-point registers, x0-x31. r0 and x0 were both hardwired to zero, and r1 was dedicated to holding the return address.
r0 - constant 0 (hardware)
r1 - return address (set by hardware)
r2-r9 - called procedure parameter registers
r10-r13 - called procedure temporary registers (scratch)
r14-r25 - calling procedure reserved registers (preserved by
callee, if used)
r26-r29 - reserved by linker
r30 (fp) - frame pointer
r31 (sp) - stack pointer
An ABI called the 88open BCS (binary compatibility standard) was defined.
bsr displ r1 <- address of first instruction after bsr;
pc <- address of bsr + displ<<2
jsr reg r1 <- address of first instruction after bsr;
pc <- contents of register
jmp reg pc <- contents of register
delayed branch forms
bsr.n displ r1 <- address of second instruction after bsr
pc <- address of bsr + displ<<2
jsr.n reg r1 <- address of second instruction after bsr
pc <- contents of register
jmp.n reg pc <- contents of register
Up to eight parameter are passed in the registers r2-r9. Additional parameters are passed on the memory stack (although some systems apparently allowed up to twelve register-allocated parameters in r2-r13).
...
... place parameters in r2-r9 ...
bsr subr ! save return address in r1
...
subr:
! prolog:
subu #r31,#r31,48 ! adjust stack pointer by size of frame
st #r1,#r31,36 ! save return address in M[sp+36]
st #r30,#r31,32 ! save caller's fp in M[sp+32]
addu #r30,#r31,32 ! move fp to point to old fp
... body of subroutine ...
! epilog:
subu #r31,#r30,32 ! reset sp to top of frame
ld #r1,#r31,36 ! restore return address
ld #r30,#r31,32 ! restore caller's fp
addu #r31,#r31,48 ! restore caller's sp
jmp #r1 ! return
(this is example code generated by DG/UX gcc)
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