br、jsr、ld的区别

"br"、"jsr"和"ld"是计算机指令中的三种不同类型的指令。

1. "br"指令是"Branch"的缩写，它用于实现条件跳转。当某个条件满足时，程序跳转到指定地址继续执行。例如，"beq"指令表示"Branch if Equal"，当两个操作数相等时，程序跳转到指定地址。"br"指令可以用于实现循环、分支等控制结构。

2. "jsr"指令是"Jump to Subroutine"的缩写，它用于实现函数调用。当程序执行到"jsr"指令时，它会将当前的程序计数器（PC）压入堆栈，并跳转到指定的函数地址执行。当函数执行完成后，程序会从堆栈中弹出之前保存的PC值，继续执行原来的代码。

3. "ld"指令是"Load"的缩写，它用于将数据从内存中加载到寄存器中。例如，"ld r1, 0x1000"表示将地址为0x1000的内存中的数据加载到寄存器r1中。"ld"指令可以用于实现数据的读取和存储操作。

总之，这三种指令分别用于实现条件跳转、函数调用和数据加载操作，在计算机程序的设计和编写中都有着重要的作用。

相关问题

生命游戏LC3汇编实现的代码

生命游戏（Game of Life）是一种经典的细胞动机，可以用LC3汇编语言来实现。下面是一个简单的生命游戏的LC3汇编代码示例：

.ORIG x3000

; 定义常量
WIDTH  .FILL 10
HEIGHT .FILL 10

; 定义存储空间
        .BLKW WIDTH*HEIGHT
        .BLKW WIDTH*HEIGHT

; 初始化细胞状态
INIT    LEA R0, GRID
        LEA R1, GRID_COPY
        LD R2, WIDTH
        LD R3, HEIGHT
INIT_LOOP   LDR R4, R0, #0
            STR R4, R1, #0
            ADD R0, R0, #1
            ADD R1, R1, #1
            ADD R3, R3, #-1
            BRp INIT_LOOP

; 游戏循环
GAME_LOOP   LEA R0, GRID
            LEA R1, GRID_COPY
            LD R2, WIDTH
            LD R3, HEIGHT
            JSR UPDATE_GRID

            ; 显示当前细胞状态
            JSR DISPLAY_GRID

            ; 复制GRID_COPY到GRID
            LEA R0, GRID_COPY
            LEA R1, GRID
            LD R2, WIDTH
            LD R3, HEIGHT
            JSR COPY_GRID

            BR GAME_LOOP

; 更新细胞状态
UPDATE_GRID LD R4, #0
            ST R4, COUNT_ALIVE

            LEA R0, GRID
            LEA R1, GRID_COPY
            LD R2, WIDTH
            LD R3, HEIGHT
UPDATE_LOOP LDR R4, R0, #0
            JSR COUNT_NEIGHBORS
            JSR UPDATE_CELL
            ADD R0, R0, #1
            ADD R1, R1, #1
            ADD R3, R3, #-1
            BRp UPDATE_LOOP

            RET

; 统计邻居细胞的数量
COUNT_NEIGHBORS  ST R7, SAVE_R7

                ADD R7, R7, #-1
                ST R0, SAVE_R0
                ST R1, SAVE_R1
                ST R2, SAVE_R2
                ST R3, SAVE_R3

                AND R4, R4, #0
                ADD R5, R0, #-1
                ADD R6, R1, #-1

                LD R0, WIDTH
                LD R1, HEIGHT

                ADD R2, R5, #2
                ADD R3, R6, #2
                JSR IS_VALID_CELL

                ADD R2, R5, #2
                ADD R3, R6, #1
                JSR IS_VALID_CELL

                ADD R2, R5, #2
                ADD R3, R6, #0
                JSR IS_VALID_CELL

                ADD R2, R5, #1
                ADD R3, R6, #2
                JSR IS_VALID_CELL

                ADD R2, R5, #1
                ADD R3, R6, #0
                JSR IS_VALID_CELL

                ADD R2, R5, #0
                ADD R3, R6, #2
                JSR IS_VALID_CELL

                ADD R2, R5, #0
                ADD R3, R6, #1
                JSR IS_VALID_CELL

                ADD R2, R5, #0
                ADD R3, R6, #0
                JSR IS_VALID_CELL

                LD R0, SAVE_R0
                LD R1, SAVE_R1
                LD R2, SAVE_R2
                LD R3, SAVE_R3

                LD R7, SAVE_R7
                RET

; 判断细胞是否有效
IS_VALID_CELL    ADD R4, R4, #1
                BRn INVALID_CELL
                BRp VALID_CELL

; 细胞无效
INVALID_CELL    RET

; 细胞有效
VALID_CELL      LDR R5, R1, #0
                ADD R5, R5, R4
                STR R5, R1, #0
                RET

; 更新细胞状态
UPDATE_CELL     LDR R5, R1, #0
                LDR R6, COUNT_ALIVE
                ADD R6, R6, #-1

                ADD R7, R4, #-1
                BRn CELL_DEAD

                ADD R7, R4, #-2
                BRn CELL_DEAD

                ADD R7, R4, #-3
                BRn CELL_DEAD

                ADD R7, R4, #-4
                BRn CELL_DEAD

                ADD R7, R4, #-5
                BRn CELL_DEAD

                ADD R7, R4, #-6
                BRn CELL_DEAD

                ADD R7, R4, #-7
                BRn CELL_DEAD

                ADD R7, R4, #-8
                BRn CELL_DEAD

CELL_ALIVE      ADD R5, R5, #1
                STR R5, R1, #0
                ADD R6, R6, #1
                STR R6, COUNT_ALIVE
                RET

CELL_DEAD       STR R5, R1, #0
                RET

; 显示细胞状态
DISPLAY_GRID    LEA R0, GRID
                LD R2, WIDTH
                LD R3, HEIGHT
DISPLAY_LOOP    LDR R4, R0, #0
                OUT
                ADD R0, R0, #1
                ADD R3, R3, #-1
                BRp DISPLAY_LOOP

                RET

; 复制GRID_COPY到GRID
COPY_GRID       LEA R0, GRID_COPY
                LEA R1, GRID
                LD R2, WIDTH
                LD R3, HEIGHT
COPY_LOOP       LDR R4, R0, #0
                STR R4, R1, #0
                ADD R0, R0, #1
                ADD R1, R1, #1
                ADD R3, R3, #-1
                BRp COPY_LOOP

                RET

; 存储空间
GRID            .BLKW WIDTH*HEIGHT
GRID_COPY       .BLKW WIDTH*HEIGHT

; 寄存器保存
SAVE_R0         .BLKW 1
SAVE_R1         .BLKW 1
SAVE_R2         .BLKW 1
SAVE_R3         .BLKW 1
SAVE_R7         .BLKW 1

; 统计存活细胞数量
COUNT_ALIVE     .FILL 0

.END

1. Write a LC-3 subroutine for printing “Hello” for N times. Write a main program to input N from the keyboard, call the subroutine and then output “Hello” for N times.

Here is the LC-3 subroutine for printing "Hello" for N times:

; Subroutine to print "Hello" for N times
; Input: R0 = N
; Output: None

PRINT_HELLO  AND R1, R1, #0          ; Initialize counter to 0
            LD R2, HELLO_MSG        ; Load the address of "Hello" message
LOOP        ADD R1, R1, #1          ; Increment counter
            BRz END_LOOP           ; If counter equals to 0, exit the loop
            LD R0, ASCII_NEWLINE    ; Load the ASCII code of newline character
            OUT                    ; Output newline character
            LD R0, ASCII_SPACE      ; Load the ASCII code of space character
            OUT                    ; Output space character
            LD R0, R2              ; Load the address of "Hello" message
            OUT                    ; Output "Hello" message
            BR LOOP                ; Repeat the loop
END_LOOP    RET                    ; Return from subroutine

; Data section
HELLO_MSG   .STRINGZ "Hello"
ASCII_SPACE .FILL x0020             ; ASCII code for space character
ASCII_NEWLINE .FILL x000A           ; ASCII code for newline character

And here is the LC-3 main program to input N from the keyboard, call the subroutine, and output "Hello" for N times:

; Main program to call PRINT_HELLO subroutine
; Input: None
; Output: None

            .ORIG x3000

            ; Prompt the user to input N
            LEA R0, PROMPT_MSG
            PUTS
            GETC
            OUT
            PUTS

            ; Convert ASCII to decimal
            AND R1, R1, #0
            AND R2, R2, #0
            ADD R2, R2, #-48
            ADD R1, R1, R2
            GETC
            ADD R1, R1, R1
            ADD R1, R1, R1
            ADD R1, R1, R2
            ADD R0, R1, #0

            ; Call PRINT_HELLO subroutine
            JSR PRINT_HELLO

            ; Exit program
            HALT

; Data section
PROMPT_MSG  .STRINGZ "Enter N: "

This program prompts the user to input N, converts the ASCII code to decimal, calls the PRINT_HELLO subroutine with N as the input, and outputs "Hello" for N times.