Peripherals appear as addresses in the memory map.
Peripheral registers sit at fixed addresses in the CPU's address space and are accessed like variables via pointers. Reads and writes have side effects, so use volatile and observe access sizes and ordering (memory barriers). Vendor headers provide structures.
*(volatile uint32_t*)0x40020014 = 0x20; sets a GPIO output bit.
Memory-mapped I/O lets software control peripherals by reading and writing addresses, which is how nearly all embedded code talks to hardware.
Peripherals appear as addresses in the memory map.
Memory-mapped I/O lets software control peripherals by reading and writing addresses, which is how nearly all embedded code talks to hardware.
A document listing the addresses, names and bit fields of a peripheral's registers, and it is the first thing to read when writing a driver.
Some registers are read-only or clear on read, so writing the wrong way can change the behaviour or lose status flags.
Typical applications include configuring a GPIO port by writing to its register at a fixed address, reading a sensor data register that a peripheral updates and setting a timer period by writing to its control register.
Study "Embedded C programming" first (topic 71 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
Linker scripts define regions. Bit-banding. Read-modify-write races.
*(volatile uint32_t*)0x40020014 = 0x20; sets a GPIO output bit.
The next topic is "Bootloaders and startup code", which builds directly on this one.
It is classed as Advanced in Electronics & Embedded (topic 72 of 104). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Electronics & Embedded.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.