Working with Hardware and SoC Layer

Understanding the Role of DTS (Device Tree Source)

Role:

• Describes hardware components (e.g., CPU, memory, GPIOs) in a .dts file.
• Compiled into a Device Tree Blob (DTB) for kernel and U-Boot.
• Enables hardware abstraction across SoCs.

Integrating Vendor SDKs and Drivers

Process:

• Vendor SDKs provide drivers and firmware for SoCs (e.g., MediaTek, Qualcomm).
• Integrated via OpenWRT’s build system (make menuconfig).
• Challenges include proprietary blobs and GPL compliance.

Flash Layout and MTD Subsystem

MTD (Memory Technology Device):

• Manages flash storage (e.g., NOR, NAND).
• Partitions include kernel, rootfs, and overlay.
• Supports JFFS2, UBIFS for writable storage.

GPIO, UART, and Other Peripheral Interfaces

Interfaces:

• GPIO: Controlled via /sys/class/gpio or device-specific drivers.
• UART: Used for serial console access.
• Others: I2C, SPI, and USB supported via kernel drivers.

Memory and CPU Optimization for Low-End Devices

Optimizations:

• Kernel configured for minimal footprint (e.g., disabled unused modules).
• musl libc reduces memory usage.
• Swap support on external storage for low-RAM devices.

Case Study: Porting OpenWRT to a New Board

Steps:

• Create a DTS file for the new board.
• Integrate vendor SDK and drivers.
• Configure build system for the target SoC.
• Test via QEMU or physical hardware.