GMS30C2116 Datasheet, PDF (98/322 Pages) Hynix Semiconductor – USERS MANUAL

3-34
CHAPTER 3
3.27 Call Instruction
The Call instruction causes a branch to a subprogram.
The branch address Rs + const, or const alone if Rs denotes the SR, is placed in the
program counter PC. The old PC containing the return address is saved in Ld; the old
supervisor-state flag S is also saved in bit zero of Ld. The old status register SR is saved in
Ldf; the saved instruction-length code ILC contains the length (2 or 3) of the Call
instruction.
Then the frame pointer FP is incremented by the value of the Ld-code (Ld-code = 0 is
interpreted as Ld-code = 16) and the frame length FL is set to six, thus creating a new stack
frame. The cache-mode flag M is cleared. All condition flags remain unchanged. Then
instruction execution proceeds at the branch address placed in the PC.
The value of the Ld-code must not exceed the value of the old FL (FL = 0 is interpreted as
FL = 16), otherwise the beginning of the register part of the stack at the SP could be
overwritten without any warning. Bit zero of const must be 0.
Rs and Ld may denote the same register.
Format Notation
Operation
LRconst CALL Ld, Rs, const
or CALL Ld, 0, const
if Rs denotes not SR then
PC := Rs + const;
else
PC := const;
Ld := old PC(31..1)//old S;
-- Ld-code 0 selects L16
Ldf := old SR;
FP := FP + Ld code;
-- Ld-code 0 is treated as 16
FL := 6;
M := 0;
Note: At the new stack frame, the saved PC is located in L0 and the saved SR is located in
L1.
A Frame instruction must be executed immediately after a Call instruction, otherwise an
Interrupt, Parity Error, Extended Overflow or Trace exception could separate the Call from
the corresponding Frame instruction before the frame pointer FP is decreased to include
(optionally) passed parameters. After a Call instruction, an Interrupt, Parity Error,
Extended Overflow or Trace exception is locked out for one instruction regardless of the
interrupt lock flag L.
_Main:
FRAME L4, L0
MOVDL2, G10
CALL
L6, 0, Sub_Start
MOVDG10, L2
RET
PC, L0
; PC = Sub_Start
Sub_Start: FRAME
MOVI L2,
RET
L3, L0
$124
PC, L0