C166/ST10 Cross-Assembler, Linker/Locator, Utilities ... - Tasking

• • • • • • • •
Assembly Language 4−11
Using non−sequential instructions (branches) within extend blocks can
cause unexpected results. Branching from extend blocks, causes the block
to be continued at the target address of the branch. Such a continued
block is called a ’virtual extend block’.
The assembler issues a warning when a branch instruction occurs in an
extend block and the branch instruction was not the final instruction in
that block.
Example:
CMP R0, #value
EXTR #4
JMP cc_EQ, VirtualEXTRBlock
MOV PT0, #value0 ; Extended SFR
MOV PT1, #value1 ; Extended SFR
MOV PT2, #value2 ; Extended SFR
MOV P3, #value3 ; Standard SFR
JMP cc_UC, Continue
VirtualEXTRBlock:
EXTRV#3 ; Virtual extend
ADD PT0, #1 ; Extended SFR
ADD PT1, #1 ; Extended SFR
ADD PT2, #1 ; Extended SFR
ADD
Continue:
P3, #1 ; Standard SFR
4.5.2 NESTING EXTEND BLOCKS
If an extend instruction occurs within an extend block the assembler issues
a warning, unless the instruction is the final instruction of the extend block
and it has the same type as the previous extend instruction. If an extend
instruction is the last instruction in an extend block and it has the same
type as the previous extend instruction, the extend block is expanded with
the new block.
Example:
ATOMIC #4
NOP
NOP
NOP
ATOMIC #2
NOP
NOP