Freescale Semiconductor StarCore SC140 - Manual (Page 425)

BTD
SC140 DSP Core Reference Manual A-111
BTD
Branch If True Using a Delay Slot (AGU)
BTD
Description
Status and Conditions that Affect Instruction
Status and Conditions Changed by Instruction
None.
Example
BTD lbl
Operation Assembler Syntax
If T==1, then PC + displacement
→ PC
BTD BTD >label
BTD
BTD >label
Branches to label if the true bit is set. If the T bit is set, the program continues executing at location
PC + displacement. If the T bit is cleared, the PC is updated to point to the next execution set, and the
program continues executing sequentially. The displacement, calculated by the assembler and linker, is a
two’s complement integer that represents the relative distance from the current PC to the destination label.
The assembler determines if the PC relative displacement is a short branch(
8
≤ displacement < 2
8 ,
W]) or a long branch (
>label [–2
20
≤ displacement < –2
8 , W and 2 8
≤ displacement < 2
20 , W]). The
execution set in the delay slot immediately following the BTD instruction is executed unconditionally after
the execution set containing the BTD instruction.
Register Address Bit Name Description
SR[1] T True bit
Instruction Result
cmpeq.w #$35,d1 Equal, so T bit in SR set.
btd lbl move.w #$29,d1 Branch taken, move.w executed, d1=$29.
inc d1 Increment executed in the delay slot, d1=$2A.
move.w #$47,d2 Skipped over.
- - - - Skipped over.
- - - - Skipped over.
- - - - Skipped over.
lbl move.w #$1A,d4 Execution continues here at lbl.
Register/Memory Address Before BTD After
SR $00E0 0002