Motorola DSP56000 manual Bit Manipulation Instructions, Loop Instructions

INSTRUCTION GROUPS

6.4.3 Bit Manipulation Instructions

The bit manipulation instructions test the state of any single bit in a memory location or a register and then optionally set, clear, or invert the bit. The carry bit of the CCR will contain the result of the bit test. The following list defines the bit manipulation instructions:

BCLR	Bit Test and Clear
BSET	Bit Test and Set
BCHG	Bit Test and Change
BTST	Bit Test on Memory and Registers

6.4.4 Loop Instructions

The hardware DO loop executes with no overhead cycles after the DO instruction itself has been executed– i.e., it runs as fast as straight-line code. Replacing straight-line code with DO loops can significantly reduce program memory. The loop instructions control hardware looping by 1) initiating a program loop and establishing looping parameters or by 2) restoring the registers by pulling the SS when terminating a loop. Initialization includes saving registers used by a program loop (LA and LC) on the SS so that program loops can be nested. The address of the first instruction in a program loop is also saved to allow no-overhead looping. The loop instructions are as follows:

DO	Start Hardware Loop
ENDDO	Exit from Hardware Loop

Both static and dynamic loop counts are supported in the following forms:

DO	#xxx,Expr	; (Static)
DO	S,Expr	; (Dynamic)

Expr is an assembler expression or absolute address, and S is a directly addressable reg- ister such as X0.

The operation of a DO loop is shown in Figure 6-13.When a program loop is initiated with the execution of a DO instruction, the following events occur:

1.The stack is pushed.

A.The SP is incremented.

B.The current 16-bit LA and 16-bit LC registers are pushed onto the SS to allow nested loops.

C.The LC register is initiated with the loop count value specified in the DO instruction.

MOTOROLA INSTRUCTION SET INTRODUCTION 6 - 25