Writing an OS Kernel from Scratch | Audio Subsystem — How ALSA Plays Sound Have you ever wondered about this process: When playing a song, how does the CPU turn digital signals into vibrations from the speaker? From WAV/MP3 files to music in your headphones, there’s sampling rate, bit depth, alsa-lib, the ALSA driver, HDA... » read more

B08 — Memory Layout of Kernel Space and User Space: vmalloc vs kmalloc Key Insight: The division of virtual address space is one of the most important OS design decisions. x86-64 Virtual Address Space Layout Modern Linux uses a 48-bit virtual address space. User space and kernel space each have separate regions: x86-64 虚拟地址空间布局： 0x0000000000000000... » read more

title: [Writing an OS Kernel from Scratch] 337 – DRAM Training: From Principles to Debugging category: os tag: [dram, ddr, embedded, signal-integrity] source: https://github.com/golang12306/os-kernel-from-scratch [Writing an OS Kernel from Scratch] 337 – DRAM Training: From Principles to Debugging 1. What Is DRAM Training? DRAM Training is the process where the DDR controller automatically adjusts signal... » read more

Writing an OS Kernel from Scratch | Virtual Memory — The Complete Journey of Paging and Linear Addresses You write int *p = (int*)0x00401000; *p = 42; — is this address a real physical address? How does the operating system ensure every process feels it has 4GB of memory when there’s actually only 8GB of... » read more

H01 — How Memory Modules Plug Into the Motherboard: DIMM Structure and Socket Design Key Insight: Behind every visible interface lie countless electrical conventions. DIMM Full Name and Basic Concepts DIMM = Dual Inline Memory Module. DIMM vs SIMM： SIMM（Single Inline Memory Module）： - 单面引脚（只能接触一侧的触点） - 72-pin 或 30-pin（早期） - 只能提供 32-bit 或 16-bit 数据宽度... » read more

Writing an OS Kernel from Scratch | I2C Bus — The Blood Vessels of Embedded Systems Have you ever wondered: How does a gyroscope chip or touchscreen communicate with the main controller? They are not as complex as USB, nor do they need the massive bandwidth of PCIe — they use I2C. I2C (Inter-Integrated Circuit)... » read more

K12 — Memory Fragmentation and Compaction: Why Large Memory Allocations Fail Key Insight: Fragmentation is the chronic disease of memory — it doesn’t hurt normally, but when it flares up, it can be fatal. What Is Memory Fragmentation Memory fragmentation refers to the presence of many “small holes” in memory that make it impossible to... » read more

A09 — Memory Barriers and Cache Coherence: Out-of-Order Access on Multi-Core Key Insight: In a multi-core CPU, the memory order you observe is not necessarily the true order. Out-of-Order Memory Access on Multi-Core CPUs Modern CPUs reorder memory access instructions for performance optimization. In multi-core programs, this reordering can cause serious problems. 内存访问乱序的例子： 线程 A：... » read more

Writing an OS Kernel from Scratch | SPI Bus — High-Speed Serial Communication Have you ever wondered: How does a NOR Flash chip exchange data with the CPU? It has no address lines, no complex master-slave protocol — just 4 wires, yet it can transfer data at tens of MHz. This is SPI (Serial Peripheral... » read more

Writing an OS Kernel from Scratch | Clocksource Framework — How Linux Picks the Best Clock Source Among TSC, HPET, and LAPIC Have you ever encountered this strange phenomenon: On a multi-core machine, calling clock_gettime(CLOCK_MONOTONIC) twice in succession actually returns time that went backwards? Or in a virtual machine, the system time suddenly “jumps” and... » read more

B11 — Modern Computer Memory Layout: Complete Virtual to Physical Address Mapping Key Insight: Understanding memory layout is the key to understanding system design. Evolution from Physical to Virtual Addressing Early computers (before the 80286) had no MMU. They directly used physical addresses. Later, segmentation was introduced, then paging, making memory layouts increasingly complex. 内存布局的演进：... » read more

A02 — Internal Structure of the Heap: Arena, Bin, and Chunk Key Insight: The heap managed by malloc is a precision system of bins and chunks. Structure of malloc_chunk malloc 把内存分成 chunk（块）来管理： struct malloc_chunk { INTERNAL_SIZE_T prev_size; // 前一个 chunk 的大小（如果前一个空闲） INTERNAL_SIZE_T size; // 本 chunk 大小 + 标志位 malloc_chunk *fd; // 同 bin 的下一个... » read more

# Writing an OS Kernel from Scratch – Part 22: Device Model and devfs — Unified Management of All Hardware Devices Writing an OS Kernel from Scratch – Part 22: Device Model and devfs — Unified Management of All Hardware Devices “Your kernel has UART, VGA, IDE, TTY, but they all operate independently with no... » read more

Understanding Low-Level Principles – Memory Series | S06 | How DDR5 Doubles Memory Bandwidth Compared to DDR4 Key Insight: Every new generation of memory standard is essentially bargaining with the laws of physics — when bandwidth is insufficient, find a new way to “squeeze” more data through. 1. The Bandwidth Improvement Formula Memory bandwidth calculation... » read more

# A06 — new/delete 和 malloc/free: C++ memory management的Difference **金句**: new 不是 malloc, delete 不是 free — 它们不只是allocate, 还有构造和析构. — ## new 和 malloc 的Essential Difference “` new 和 malloc 的区别： malloc： – C 库函数 – 只分配内存，不初始化 – 返回 void* – 失败返回 NULL new： – C++ 关键字 – 分配内存 + 调用构造函数 – 返回具体类型的指针（不需要类型转换） – 失败抛出... » read more

330 – Deep Dive into Android Boot Process: From Power-On to the First App Series Navigation: 331-Bootloader | 332-init Process | 333-Zygote Have you ever thought about this: From the moment you press the power button until the desktop wallpaper appears on screen, what does the Android system go through? This is a complete chain... » read more

H04 — XMP and EXPO: How Memory Overclocking Works, and Why a 3200-rated Stick Can Run at 3600 Key Insight: Bought a 3200-rated stick, runs at 3600. It’s not magic; it’s engineering. Why Memory Has Both JEDEC and XMP Frequencies When buying memory, you see DDR4-3200 on the specs, but you can actually set it... » read more

# Writing an OS Kernel from Scratch – Part 33: e1000 NIC Driver — Connect Your OS to the Network World! “An operating system without a network is just an information island. Today, we implement the Intel e1000 NIC driver, letting MyOS ping the outside world!” In previous chapters, we built a complete desktop system:... » read more

K11 — The Full Path of Physical Page Allocation: alloc_pages and the Buddy System Key Insight: Every call to alloc_pages embarks on a complete journey from request to physical page frame. The alloc_pages Function Signature alloc_pages is the core function for allocating physical pages in Linux: struct page *alloc_pages(gfp_t gfp_mask, unsigned int order); Parameters: -... » read more

title: [Writing an OS Kernel from Scratch] 335 – ARM Architecture Boot: From Power-On to Kernel category: os tag: [arm, boot, embedded, u-boot] source: https://github.com/golang12306/os-kernel-from-scratch [Writing an OS Kernel from Scratch] 335 – ARM Architecture Boot: From Power-On to Kernel 1. ARM Boot Sequence Overview Embedded device boot is a layered relay race. To understand... » read more