mips知识点
知识点
寄存器地址：
伪指令
- **.data：**用于预先存储数据的伪指令的开始标志。
- **.text：**程序代码指令开始的标志。
- **.word：**以字为单位存储数据。
- **.asciiz：**以字节为单位存储字符串。
- **.space：**申请若干个字节的未初始化的内存空间。
V0 的不同值
常用：
| Service | Code in $v0 | Arguments | Result |
|---|---|---|---|
| print integer | 1 | $a0 = integer to print | |
| print float | 2 | $f12 = float to print | |
| print double | 3 | $f12 = double to print | |
| print string | 4 | $a0 = address of null-terminated string to print | |
| read integer | 5 | $v0 contains integer read | |
| read float | 6 | $f0 contains float read | |
| read double | 7 | $f0 contains double read | |
| read string | 8 | $a0 = address of input buffer $a1 = maximum number of characters to read | See note below table |
| sbrk (allocate heap memory) | 9 | $a0 = number of bytes to allocate | $v0 contains address of allocated memory |
| exit (terminate execution) | 10 | ||
| print character | 11 | $a0 = character to print | See note below table |
| read character | 12 | $v0 contains character read | |
| open file | 13 | $a0 = address of null-terminated string containing filename $a1 = flags $a2 = mode | $v0 contains file descriptor (negative if error). See note below table |
| read from file | 14 | $a0 = file descriptor $a1 = address of input buffer $a2 = maximum number of characters to read | $v0 contains number of characters read (0 if end-of-file, negative if error). See note below table |
| write to file | 15 | $a0 = file descriptor $a1 = address of output buffer $a2 = number of characters to write | $v0 contains number of characters written (negative if error). See note below table |
| close file | 16 | $a0 = file descriptor | |
| exit2 (terminate with value) | 17 | $a0 = termination result | See note below table |
| Services 1 through 17 are compatible with the SPIM simulator, other than Open File (13) as described in the Notes below the table. Services 30 and higher are exclusive to MARS. | |||
| time (system time) | 30 | $a0 = low order 32 bits of system time $a1 = high order 32 bits of system time. See note below table | |
| MIDI out | 31 | $a0 = pitch (0-127) $a1 = duration in milliseconds $a2 = instrument (0-127) $a3 = volume (0-127) | Generate tone and return immediately. See note below table |
| sleep | 32 | $a0 = the length of time to sleep in milliseconds. | Causes the MARS Java thread to sleep for (at least) the specified number of milliseconds. This timing will not be precise, as the Java implementation will add some overhead. |
| MIDI out synchronous | 33 | $a0 = pitch (0-127) $a1 = duration in milliseconds $a2 = instrument (0-127) $a3 = volume (0-127) | Generate tone and return upon tone completion. See note below table |
| print integer in hexadecimal | 34 | $a0 = integer to print | Displayed value is 8 hexadecimal digits, left-padding with zeroes if necessary. |
| print integer in binary | 35 | $a0 = integer to print | Displayed value is 32 bits, left-padding with zeroes if necessary. |
| print integer as unsigned | 36 | $a0 = integer to print | Displayed as unsigned decimal value. |
| (not used) | 37-39 | ||
| set seed | 40 | $a0 = i.d. of pseudorandom number generator (any int). $a1 = seed for corresponding pseudorandom number generator. | No values are returned. Sets the seed of the corresponding underlying Java pseudorandom number generator (java.util.Random). See note below table |
| random int | 41 | $a0 = i.d. of pseudorandom number generator (any int). | $a0 contains the next pseudorandom, uniformly distributed int value from this random number generator’s sequence. See note below table |
| random int range | 42 | $a0 = i.d. of pseudorandom number generator (any int). $a1 = upper bound of range of returned values. | $a0 contains pseudorandom, uniformly distributed int value in the range 0 = [int] [upper bound], drawn from this random number generator’s sequence. See note below table |
| random float | 43 | $a0 = i.d. of pseudorandom number generator (any int). | $f0 contains the next pseudorandom, uniformly distributed float value in the range 0.0 = f 1.0 from this random number generator’s sequence. See note below table |
| random double | 44 | $a0 = i.d. of pseudorandom number generator (any int). | $f0 contains the next pseudorandom, uniformly distributed double value in the range 0.0 = f 1.0 from this random number generator’s sequence. See note below table |
| (not used) | 45-49 | ||
| ConfirmDialog | 50 | $a0 = address of null-terminated string that is the message to user | $a0 contains value of user-chosen option 0: Yes 1: No 2: Cancel |
| InputDialogInt | 51 | $a0 = address of null-terminated string that is the message to user | $a0 contains int read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field |
| InputDialogFloat | 52 | $a0 = address of null-terminated string that is the message to user | $f0 contains float read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field |
| InputDialogDouble | 53 | $a0 = address of null-terminated string that is the message to user | $f0 contains double read $a1 contains status value 0: OK status -1: input data cannot be correctly parsed -2: Cancel was chosen -3: OK was chosen but no data had been input into field |
| InputDialogString | 54 | $a0 = address of null-terminated string that is the message to user $a1 = address of input buffer $a2 = maximum number of characters to read | See Service 8 note below table $a1 contains status value 0: OK status. Buffer contains the input string. -2: Cancel was chosen. No change to buffer. -3: OK was chosen but no data had been input into field. No change to buffer. -4: length of the input string exceeded the specified maximum. Buffer contains the maximum allowable input string plus a terminating null. |
| MessageDialog | 55 | $a0 = address of null-terminated string that is the message to user $a1 = the type of message to be displayed: 0: error message, indicated by Error icon 1: information message, indicated by Information icon 2: warning message, indicated by Warning icon 3: question message, indicated by Question icon other: plain message (no icon displayed) | N/A |
| MessageDialogInt | 56 | $a0 = address of null-terminated string that is an information-type message to user $a1 = int value to display in string form after the first string | N/A |
| MessageDialogFloat | 57 | $a0 = address of null-terminated string that is an information-type message to user $f12 = float value to display in string form after the first string | N/A |
| MessageDialogDouble | 58 | $a0 = address of null-terminated string that is an information-type message to user $f12 = double value to display in string form after the first string | N/A |
| MessageDialogString | 59 | $a0 = address of null-terminated string that is an information-type message to user $a1 = address of null-terminated string to display after the first string | N/A |
注释：服务编号为30及以上的服务不包含在SPIM服务8中。它遵循UNIX 'fgets’的语义。对于指定长度n，字符串的长度不能超过n-1。如果长度小于n-1，则在末尾添加换行符。在任何情况下，都会用空字符填充。如果n等于1，则忽略输入并将空字符放置在缓冲区地址上。如果n大于1，则忽略输入并且不会将任何内容写入缓冲区。
服务11 - 打印低字节所对应的ASCII字符。
服务13 - MARS实现了三个标志值：0表示只读，1表示可写且可创建，9表示可写且可创建和追加。它忽略模式。如果操作失败，则返回的文件描述符将为负数。底层文件I/O实现使用java.io.FileInputStream.read()读取和java.io.FileOutputStream.write()写入。MARS内部维护文件描述符，并从3开始分配它们。文件描述符0、1、2始终用于：从标准输入读取、向标准输出写入和向标准错误写入（自版本4.3起新增）。
服务13、14、15 - 在MARS 3.7中，结果寄存器已更改为与SPIM兼容。之前在《计算机组织与设计》的附录B中错误地印成了$a0，现在是$a1。
服务17 - 如果MIPS程序在MARS图形界面（GUI）的控制下运行，则忽略$a1中的退出代码。服务30 - 系统时间来自java.util.Date.getTime()，表示自1970年1月1日以来的毫秒数。
服务31、33 - 通过声卡模拟MIDI输出。详情见下文。
服务40至44使用Java底层的伪随机数生成器，由java.util.Random类提供。每个流（由$a0的内容标识）都由不同的Random对象模拟。没有默认的种子值，因此如果需要重复的随机序列，请使用Set Seed服务（40）。
常用指令
str: .asciiz “The numbers are:\n”
# 这里使用了宏，%i 为存储当前行数的寄存器，%j 为存储当前列数的寄存器 # 把 (%i * 8 + %j) * 4 存入 %ans 寄存器中
.macro getindex(%ans, %i, %j)
sll %ans, %i, 3 #%ans = %i * 8
add %ans, %ans, %j #%ans = %ans + %j
sll %ans, %ans, 2 # %ans = %ans * 4 .end_macro
在汇编程序中，还有一种和C语言中 #define 类似的宏定义，一般用于常量的定义上，那就是 .eqv。.eqv 用法如下：
.eqv EQV_NAME string
li $t0, 0 # $t0=0
la $a0, str 地址
beq $t0, $s0, loop_in_end # $t0 == $s0 的时候跳出循环
bne 不相等时
array: .space 40 # 存储这些数需要用到数组，数组需要使用 10 * 4 = 40 字节 # 一个 int 整数需要占用 4 个字节，需要存储 10 个 int 整数 # 因此，array[0] 的地址为 0x00，array[1] 的地址为 0x04 # array[2] 的地址为 0x08，以此类推。
sll $t1, $t0, 2 # $t1 = $t0 << 2，即 $t1 = $t0 * 4
sw $v0, array($t1) # 把输入的数v0存入地址为 array + $t1 的内存中
lw $a0, array($t1) # 把内存中地址为 array + $t1 的数取出到 $a0 中
addi $t0, $t0, 1 # $t0 = $t0 + 1
add $t0, $t0, $a0 # $t0 = $t0 + $a0
jal f #跳转到函数f，并且将$ra变为下一句地址
jr $ra 跳转到寄存器$ra
