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ST9 USER GUIDE

if the condition is not met. If the condition is met, the pointer is not incremented and the branch

is taken. Example:

; Find the position of a letter in a text.

Message:.ascii "This is a trial"

rr0,#Message

; where to search

r2,#'t'

; the character to search for

Search:

cpjfi

r2,(rr0),Search

; this is the search loop

...

; here rr0 points to the 11th character of message

...

; continuation

3.3.1.7 Far Branch

As explained in Section 3.1.7, the 4-Mbyte memory is a segmented memory. It is not possible

to reach another segment with the common CALL, RET and JP instructions because they do

not manage the CSR (Code Segment Register) register. This is managed by the three new

CALLS, RETS and JPS instructions. Only 2 to 4 cycles are added to the common instructions.

3.3.1.8 Optimized C Instructions

In C functions when a function is called, the compiler needs to push the variables in the user/

system stacks and to keep the return address location of the function inside the stack.

Therefore, a frame pointer is used, and 2 pieces of code named prologue and epilogue need

to be added by the C Compiler at the beginning and at the end of the function respectively.

The LINK and UNLINK instructions (LINKU, UNLINKU to use the user stack) are used to re-

duce the code overhead generated by the compiler inside the function. These instructions are

automatically added by the C Compiler instead of prologue and epilogue (if option -mlink is

specified).

The number of cycles gained by using these instructions is about 34 to 42 cycles and 8 bytes

per called function.

ST9 데이터시트(PDF) 39 Page - STMicroelectronics