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ARMv8体系结构学习

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发表于 2018-5-30 13:02:49 | 显示全部楼层 |阅读模式
ARM体系结构属于一种RISC体系结构,RISC体系结构具有如下三个基本特征:
1)具有一个比较大的通用 寄存器文件;
2)load/store指令,所有数据处理指令的操作数只能是寄存器,不能是内存单元;
3)单一地址模型,所有load/store指令的地址计算仅仅依赖指令本身或寄存器操作数。

ARM面向三种不同应用领域定义了不同系列的体系结构:
A        应用领域
        支持基于MMU的虚拟内存系统,支持A64,A32和T32指令集
R        实时领域
        支持基于MPU的保护内存系统,支持A32和T32指令集
M   微控制器领域
        具有低延迟中断处理技术(包括基于硬件寄存器实现的堆栈,支持高级语言实现中断处理函数)
        具有R的部分技术
        支持T32部分指令集

ARMv8属于面向应用领域的系列,支持两种执行态:
AAarch64        64位执行态
AAarch32        32位执行态,用于向前兼容ARMv7-A

这两种执行态都支持SIMD和浮点指令
AArch64的SIMD指令只能采用128位SIMD/浮点寄存器作为操作数。
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 楼主| 发表于 2018-5-30 13:30:21 | 显示全部楼层
执行态
        执行态定义了流水线相关的内容,包括:寄存器宽度、指令集、异常模型、虚拟内存系统结构和程序员模型。AArch64是ARMv8的64位执行态,主要特征有:
1)31个64位通用寄存器,其中X30常用于过程链接寄存器;
2)一个64位程序计数寄存器、若干64位堆栈寄存器、和若干异常链接寄存器;
3)32个128位寄存器,用于SIMD向量/标量浮点计算。
4)支持A64指令集;
5)有4种异常级别(又称特权级别)EL0~EL3;
6)支持64位虚拟地址空间;
7)提供若干PSTATE单元,用于处理器状态的保存和恢复,A64指令集包含了对每个PSTATE单元操作的指令。
8)每个寄存器都有一个异常级别的后缀,用于表明对该寄存器操作所需的最低异常级别要求。

AArch64和AArch32两种执行态之间可以动态切换。
当自陷到高级异常级别时,执行态要么保持一直要么从AArch32切换到AArch64;
当从高级异常级别返回时,执行态要么保持一直要么从AArch64切换到AArch32。
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 楼主| 发表于 2018-5-30 13:41:07 | 显示全部楼层
系统寄存器
        系统寄存器的名称格式:<寄存器名称>_ELx,x是0/1/2/3的异常级别。系统寄存器包括:
1)系统控制寄存器;
2)调试寄存器;
3)性能监控寄存器(可选);
4)通用定时器寄存器;
5)跟踪寄存器(可选);
6)通用中断控制器CPU接口寄存器(可选);
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 楼主| 发表于 2018-6-12 10:01:41 | 显示全部楼层
ARMv8提供两个寄存器文件:通用寄存器文件和SIMD和浮点寄存器文件。
在AArch64执行态
         支持31个通用寄存器,64位Xn或32位 Wn,其中32位Wn是Xn的低32位;
         支持32个SIMD和浮点寄存器,128位 Vn。
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 楼主| 发表于 2018-6-12 10:04:07 | 显示全部楼层
整型数据类型
8位字节
16位半字
32位全字(用32位Wn)
64位双字( 用64位Xn)
128位四字 (用128位Vn)
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 楼主| 发表于 2018-6-12 10:07:03 | 显示全部楼层
本帖最后由 ubuntu 于 2018-6-12 10:10 编辑

向量数据类型 ,只能用浮点寄存器操作向量数据类型,向量数据类型包含了单元和最大索引号两个特征,每个单元对应一个索引号(索引号从0到最大索引号)。单元数据类型由向量指令决定,单元数量,即最大索引号+1,依赖于单元数据类型和向量寄存器长度决定。
                           向量数据类型的长度 = 单元数据类型 x (最大索引号 + 1)

                               
        向量数据类型的长度为128位时,寄存器Vn{.2D.4S.8H16B}
        向量数据类型的长度为64位时,寄存器Vn{.1D.2S.4H.8B}


armv8 SIMD和浮点寄存器

armv8 SIMD和浮点寄存器
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 楼主| 发表于 2018-6-12 10:11:36 | 显示全部楼层
浮点数据类型

                                                  16位半精度                32位单精度                   64位双精度
                符号域S                               [15]                         [31]                                [63]
                指数域exponent           [14:10]                        [30:23]                        [62:52]
                小数域fraction                    [9:0]                        [22:0]                        [51:0]

浮点数据类型只能使用128位Vn寄存器;
半精度类型只能用于和其他浮点格式进行格式转换,不能用于其他数据处理操作。
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发表于 2018-12-20 18:00:12 | 显示全部楼层
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发表于 2018-12-22 08:43:40 | 显示全部楼层
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