MCU

Many peripheral problems do not look like clock problems at first.

UART baud rate is slightly wrong. SPI fails when the rate is raised. I2C occasionally times out. A timer period drifts. ADC sampling does not match the expected rate. The CPU runs at a high frequency, but peripheral register access is still slow. A more subtle case: everything works before sleep, but the first peripheral access after wakeup fails, or a UART works in the bootloader and then stops working once the operating system takes over.

Many MCU projects do not need a full platform at the beginning. Their first problems are concrete:

• the main loop grows and response becomes slower
• UART, sensors, wireless stacks, and storage paths interfere with each other
• ISR code should stay short, but tasks do not know when to run
• one slow peripheral wait delays unrelated logic
• timers, timeouts, retries, and low power become tangled

FreeRTOS often becomes the first RTOS because it separates the concurrency paths that first become unmanageable in bare-metal firmware.