How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?
How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?
How Do W55MH32 and W5500 Registers Enable Bare-Metal TCP Communication?
Register, Buffer, and Socket Lifecycle Understanding for Reliable Ethernet Firmware
(W55MH32와 W5500 레지스터는 베어메탈 TCP 통신을 어떻게 가능하게 하는가?)
Summary (40–60 words)
This article explains how the W55MH32 MCU works with the WIZnet W5500 Ethernet controller at the register and buffer level to implement TCP communication on bare-metal systems. By understanding SPI access patterns, TX/RX buffer management, and the hardware TCP socket lifecycle, developers can build reliable Ethernet firmware without complex software TCP/IP stacks.
1. Why Register-Level Understanding Still Matters
In many embedded projects, Ethernet is treated as a “black box” behind libraries.
However, on bare-metal systems, long-term stability depends on understanding:
How registers are accessed over SPI
How TX/RX buffers are organized
How TCP sockets transition through states
The W55MH32 + W5500 combination is a classic example where:
Understanding the hardware design directly translates to simpler, more reliable firmware.
2. System Architecture Overview
Bare-Metal Ethernet Architecture
Key architectural property:
No software TCP/IP stack exists on W55MH32
TCP/IP is fully implemented in W5500 hardware
Firmware controls the network entirely through registers
3. SPI Access Model of W5500
Every interaction with the W5500 happens via SPI frames, consisting of:
16-bit address (block offset)
Control byte
Block select
Read/write flag
Variable or fixed data mode
Data bytes
Why This Matters
SPI framing defines atomic operations.
Breaking a frame incorrectly causes:
Corrupted register writes
Invalid buffer pointers
Silent TCP failures
A correct driver enforces:
One logical operation = one CS assertion
4. W5500 Register Blocks and Their Roles
W5500 internally divides memory into logical blocks:
Common Registers
MAC address
IP address
Gateway, subnet
Interrupt configuration
Socket Registers (8 identical sets)
Mode (TCP/UDP)
Port numbers
Destination IP/port
Command & status registers
TX Buffers / RX Buffers
16 KB TX shared
16 KB RX shared
Understanding this structure eliminates guesswork.
5. TX/RX Buffer Model: Why TCP Becomes Simple
Unlike software stacks, W5500 exposes TCP buffers directly.
TX Path (Conceptual)
RX Path (Conceptual)
Key insight:
TCP reliability is guaranteed by hardware once pointers are correct.
6. TCP Socket Lifecycle in Hardware
Each W5500 socket implements a full TCP state machine:
On bare-metal firmware:
W55MH32 does not manage TCP states
It only:
Writes socket commands
Polls status registers
Moves buffer pointers
This dramatically reduces firmware complexity.
7. Typical Bare-Metal TCP Flow (W55MH32)
Initialize SPI
Configure W5500 common registers
Allocate socket and set TCP mode
Issue CONNECT or LISTEN command
Wait for ESTABLISHED state
Send and receive data via buffers
Close socket cleanly
At no point is TCP logic implemented in software.
8. Common Failure Modes (And Why They Happen)
❌ SEND returns OK, but no data received
Cause:
TX pointer not updated correctly
SPI transaction split across CS boundaries
❌ RX size shows data, but read fails
Cause:
RX read pointer not advanced
RECV command not issued
❌ Socket stuck in CLOSE_WAIT
Cause:
Firmware never processes remaining RX data
All these issues disappear when register and buffer semantics are respected.
9. Why This Design Is Ideal for Bare-Metal Systems
For W55MH32-based systems:
No RAM wasted on TCP/IP stacks
No timing jitter from software TCP
Predictable behavior
Easy debugging with logic analyzer
This makes the architecture suitable for:
Industrial controllers
Networked sensors
Long-running embedded devices
10. Key Takeaway
On bare-metal systems, W5500 turns TCP from a software problem into a register-management problem—and that is a good thing.
Once developers understand:
SPI framing
Register blocks
Buffer pointer rules
TCP and UDP communication become straightforward and reliable.
FAQ (Engineer-Focused)
Q1. Does W55MH32 run TCP/IP code?
No. All TCP/IP logic is inside the W5500.
Q2. Is register-level programming required?
Yes for bare-metal, but it greatly simplifies reliability.
Q3. How many TCP connections are supported?
Up to 8 hardware sockets.
Q4. Is this approach faster than software TCP/IP?
Yes, and far more deterministic.
Q5. Is this suitable for industrial products?
Absolutely—this is where it excels.
Source
CNBlogs article (bitconn)
WIZnet W5500 Datasheet
WIZnet W55MH32 documentation
Tags
W55MH32, W5500, WIZnet, Register-Level Ethernet, TCP Socket Lifecycle, SPI Driver, Bare-Metal Networking, Industrial Ethernet
🇰🇷 한국어 번역 (1:1 Full Translation)
W55MH32와 W5500 레지스터는 베어메탈 TCP 통신을 어떻게 가능하게 하는가?
레지스터·버퍼·소켓 생명주기로 이해하는 이더넷 펌웨어 설계
요약
본 문서는 W55MH32 MCU와 WIZnet W5500 이더넷 컨트롤러를 사용한 베어메탈 TCP 통신 구조를 설명한다. SPI 접근 방식, TX/RX 버퍼 관리, 하드웨어 TCP 소켓 생명주기를 이해함으로써, 복잡한 소프트웨어 TCP/IP 스택 없이도 안정적인 이더넷 펌웨어를 구현할 수 있음을 보여준다.
1. 왜 레지스터 수준 이해가 중요한가
베어메탈 환경에서는
하드웨어 동작을 정확히 이해하는 것이 안정성의 핵심이다.
2. 시스템 아키텍처
TCP는 소프트웨어가 아닌 하드웨어가 처리한다.
3. SPI 프레임 모델
SPI 프레임은 원자적이어야 하며
CS 분리는 허용되지 않는다.
4. 레지스터 블록 구조
공통 레지스터
소켓 레지스터
TX/RX 버퍼
5. 버퍼 기반 TCP 처리
포인터 관리만 정확하면
TCP 신뢰성은 자동으로 보장된다.
6. TCP 소켓 생명주기
소켓 상태 전이는
모두 W5500 하드웨어에서 수행된다.
7. 베어메탈 TCP 흐름
초기화 → 연결 → 송수신 → 종료
8. 대표적인 오류 원인
CS 타이밍 오류
포인터 미갱신
RECV 누락
9. 산업용 적합성
예측 가능한 동작
장시간 안정성
낮은 메모리 사용량
10. 핵심 메시지
W5500은 TCP를 소프트웨어 문제가 아닌 레지스터 관리 문제로 바꾼다.
태그
W55MH32, W5500, WIZnet, 베어메탈 TCP, 레지스터 기반 이더넷, 산업용 네트워크