饱和度指令的重要性

嗨，大家好，
你们中的许多人可能不知道PSoC 5LP中饱和指令是怎么做的。PSoC 5lp采用Cortex-M3内核有两个特殊的指令称为“SSAT”（签署饱和度）和“门”（无符号饱和）。这些指令是用来限制变量或一定数量的位值。（参考文献：
例如，如果你有一个8位的变量，当然如果你知道该变量的值不会超过127号说，你想把任何价值127以上为127本身（饱和度）和任何低于0的值为零的本身。在这种情况下，你需要其他的条件语句比较变127和采取必要的行动，以写一个大的C代码。相反，为了简化这个逻辑，你可以利用饱和assemblyinstructions，Cortex-M3（PSoC 5lp核心）支持。请注意，GCC和MDK编译器不将此指令本身等价的C代码。
例如，在上面的例子中，限制我的结果的比特数是7（2 ^ 7-1 = 127）。假设我在登记R0如果我想储存饱和导致登记R3的饱和值，我的汇编指令会
“USAT R3，8，R0”
类似的语法是签署了饱和指定一个正极限和签名变消极的限制。我希望你知道的语法包括C代码的汇编指令。
问候，Asha
注：
仅供参考，如果您想指定一个变量的一个特定的登记，语法是“登记（数据类型）* variable_name ASM（“登记名字”）；“
例如：注册UTIN 8*输出ASM（“R0”）；
DDI037EYCORTEXM3R1P1TRO.PDF
2.1兆字节



     以下为原文
  Hi All,
    Many of you may not be aware of what saturation instructions do in PSoC 5LP. PSoC 5LP uses Cortex-M3 core which has two special instructions called "SSAT" (Signed saturation) and "USAT" (Unsigned saturation). These instructions are used to limit a variable or a value to a certain number of bits. (Reference:
    For example,  if you have an 8 bit variable and for sure if you know that the value of the variable will not exceed a number 127 say, you would like to round off any value above 127 as 127 itself ( saturation) and any value below 0 as zero itself. In this case you need to write a big C code using if-else conditional statement to compare the variable with 127 and take the necessary action. Instead, to simplify this logic, you can make use of the saturation assembly instructions which Cortex-M3 (core of PSoC 5LP) supports. Please note that both GCC and MDK compilers do not append this instruction by itself for an equivalent C code.
    For example, in the above example, the number of bits to restrict my result to would be 7 (2^7-1 = 127). Assuming I have the unsaturated value in register r0 and if I would like to store the saturated result in register r3, my assembly instruction would be
    "usat r3, 8, r0"
    Similar syntax is for signed saturation for specifying a positive limit and a negative limit for a signed variable. I hope you know the syntax to include an assembly instruction in C code.
    Regards,
Asha
     
    Note:
    FYI, if you would like to assign a variable to a particular register, the syntax is "register (data type)* variable_name asm("register name");"
    For example: register uint8* output asm ("r0");

•   DDI0337E_cortex_m3_r1p1_trm.pdf 2.1 MB