A simple program to toggle an LED on GPIO pin PC13 (typical Blue Pill onboard LED) demonstrates embedded systems work:
The book The STM32F103 Arm Microcontroller and Embedded Systems: Using Assembly and C the stm32f103 arm microcontroller and embedded systems work
The blue LED pulsed on. The pollen sensor hummed. And somewhere in Shenzhen, another engineer was just learning what a bit-band region was, swearing gently at a datasheet, falling in love with the beautiful, brutal complexity of the ARM microcontroller and the embedded systems work that made it sing. A simple program to toggle an LED on
ARM® 32-bit Cortex®-M3 CPU running at a maximum frequency of 72 MHz . swearing gently at a datasheet