高通子系统subsystem基础知识

翻译了高通相关文档部分内容，结合sm4350平台项目做的总结：

1，基本概念

Subsystem

The system on chip (SoC) consists of a main APSS processor and additional processors that run on their own software. For example, on QTI SoCs, other processors that need separate software include modem, LPASS, Venus, WCNSS, GPU, and sensor low power island (SLPI). Not all these subsystems are present on all SoCs.

片上系统(SoC)由一个主APSS（Applications processor subsystem应用处理器子系统）处理器和运行自有软件的多个附加处理器组成。

例如在高通SoC上，附加处理器运行的软件包括modem,LPASS，Venus,WCNSS, GPU和SLPI.  并非所有Soc都包括这些子系统。

【modem】通信基带

【LPASS】Low power audio subsystem 低功耗音频子系统

【Venus】高通的图像处理模块

【WCNSS】Wireless Connect subsystem无线连接子系统

【SLPI】 sensor low power island 低功耗岛传感器子系统

The Peripheral Image Loader (PIL) is a framework that allows services to load and reload firmware images for each subsystem of the chipset into DDR memory.

 Upon loading, TrustZone’s services are invoked to authenticate the content of the image file using a hash segment.

Once the image is authenticated, the processor of that subsystem is taken out of reset, i.e., allowed to execute instructions.

外围镜像加载(PIL)是一个框架，它允许服务将芯片的各个子系统加载或者重载到DDR内存中。

加载镜像时tz的服务会被调用，使用一个哈希段对镜像文件的内容进行校验。