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Microprocessors and -controllers

MCU

An MCU is a group of microcontroller units that share a common architecture, design, and often the same core features

  • ARM Cortex-M is a popular MCU family, where multiple manufacturers like STMicroelectronics, NXP, and Microchip produce MCUs that are based on the ARM Cortex-M core.
  • AVR is another MCU family, famously used in the Arduino platform.
  • PIC is a family of MCUs from Microchip Technology, with a range of devices from small 8-bit controllers to more powerful 16-bit and 32-bit versions.

Within each MCU family, you’ll typically see models that differ by features like:

  • Flash memory size
  • RAM size
  • Clock speed
  • Number of GPIO pins
  • Peripheral support (e.g., UART, SPI, I2C, timers, etc.)

In-System Programming (ISP)

  • the act of programming a microcontroller while it is already mounted on the board
  • Contrary to Pre-Programming. You program the contro

CMSIS-DAP Devices are all devices that can write programs into a microcontroller's memory using JTAG or SWD. ler before soldering it somewhere.

Available Controllers

At least 5 of each:

  • SEEEDSTUDIO XIAO SAMD21 NO HDRS
  • SEEEDSTUDIO XIAO ESP32C3 NO HDRS
  • SEEEDSTUDIO XIAO ESP32S3 NO HDRS
  • SEEED STUDIO XIAO RP2040 ARDUINO
  • ATSAMD11C14A-SSUT
  • ATSAMD21E18A-AUT
  • ATTINY412-SSFR
  • ATTINY1624-SSFR
  • ATTINY3226-SU
  • AVR128DB32-I/PT
Xiao RP2040Pico RP2040ESP32C3ESP32S3SAMD21ATSAMD11C14A-SSUTATSAMD21E18A-AUTATTINY412-SSFRATTINY1624-SSFRATTINY3226-SUAVR128DB32-I/PT
TypeARMARMARM
Frequency133MHz133MHz160 MHz240 MHz48MHz48MHz48MHz20MHz20MHz20MHz24MHz
SRAM264KB264KB400 KB8MB32KB4KB32KB256B2KB3KB16KB
onboard memory2MB2MB4MB8MB256KB16KB256KB4KB16KB32KB128KB
I/O-Pins112611111112266121825/26 (1x only In)
ADC43391156691513
DAC00001111001
PackageSOIC-14TQFP-32SOIC-8SOIC-14SOIC-20TQFP-32
Price4,68 $5 $4,99 $7,49 $5,4 $1,58 $4,03 $0,59 $1,01 $1,29 $2,06 $

RP2040 (Raspberry Pi Pico)

Toolchain:

Workflow:

  1. Write code in C/C++ or Python.
  2. Build with CMake (Pico SDK) or Arduino IDE.
  3. Flash via USB (UF2 bootloader) or SWD debugger (e.g., Picoprobe).

Efficiency Tips:

  • Use Visual Studio Code with the Pico SDK extension for CMake integration.
  • Leverage Picoprobe (a second Pico) for debugging.

ESP32 (Espressif)

Toolchain:

Workflow:

  1. Develop in C/C++ (ESP-IDF) or Arduino framework.
  2. Build with ESP-IDF CLI or PlatformIO.
  3. Flash via USB (esptool.py) or OTA updates.

Efficiency Tips:

  • PlatformIO streamlines ESP-IDF/Arduino workflows.
  • Use ESP-Prog or JTAG for advanced debugging.

SAMD21/SAMD11 (Atmel/Microchip)

Toolchain:

Workflow:

  1. Code in C/C++ (Microchip Studio) or Arduino.
  2. Build and flash via USB (UF2 bootloader) or EDBG/SWD.

Efficiency Tips:

  • Use Arduino IDE for simplicity; enable verbose upload for debugging.
  • For low-level control, use CMSIS libraries in Microchip Studio.

Attiny/AVR128 (AVR Family)

Toolchain:

Workflow:

  1. Write code in C/C++ or Arduino.
  2. Compile with AVR-GCC or Arduino IDE.
  3. Flash via ISP programmer (e.g., USBasp, Arduino-as-ISP).

Efficiency Tips:

  • Use PlatformIO for project management.
  • For tinyAVR (e.g., ATtiny85), optimize code size with -Os compiler flag.

General Workflow Optimization Tips

  1. Unified Environments:

    • PlatformIO (VS Code) supports all listed MCUs, reducing toolchain setup time.
    • Arduino IDE (with board managers) simplifies entry-level development.

  2. Debugging Tools:

    • SWD/JTAG: Use for RP2040, ESP32, SAMD21 (e.g., Segger J-Link, CMSIS-DAP).
    • Serial Monitor: Essential for ESP32/RP2040 debugging.

  3. Version Control:

    • Use git for code management; track dependencies (e.g., submodules for Pico SDK).

  4. Automation:

    • Write Makefiles or use PlatformIO scripts for CI/CD pipelines.

QFP mit Beinchen seitlich
TQFP ohne Beinchen
Soic-8 8 Beinchen
Punkt oder Kerbe kennzeichnen Pin 1

Putting code onto it

In-System Programming (ISP)

  • the act of programming a microcontroller while it is already mounted on the board
  • Contrary to Pre-Programming. You program the contro

CMSIS-DAP Devices are all devices that can write programs into a microcontroller's memory using JTAG or SWD. ler before soldering it somewhere.

Serial Peripheral Interface (SPI)

  • A standard synchronous serial communication interface used for short-distance communication between a main device and one or more peripheral devices.
  • synchronous (needs clock signal), serial communication
  • multiple secondary devices are possible
  • full-duplex
  • pins:
    • MOSI (main out secondary in)
    • MISO (main in secondary out)
    • SCK (clock)
    • SS (secondary select): select which secondary device to communicate with

Serial Peripheral Data Interface (SPDI)

  • do not find any source for it

Joint Test Action Group (JTAG)

  • eletronics manufacturers committee
  • they developed a protocol with the same name
  • mostly used for programming ARM cores
  • pins
    • TMS: mode select
    • TCLK: clock
    • TDO: data out
    • TDI: data in
    • nRESET: reset (optional)

Serial Wire Debug (SWD)

  • two-pin variant of the JTAG protocol
  • most common on newer ARM chips
  • pins:
    • swdio: in/out
    • swclk: clock

Unified Program and Debug Interface (UPDI)

  • proprietary
  • single-wire,
  • bi-directional, half-duplex
  • asynchronous
  • can use off-the shelf UART adapters
  • used to program AVR microcontrollers released since 2016, ATTINY412, ATTINY164.
  • more detailed blog article
  • debugging is hidden behind a proprietary interface, but even though you can snoop on the protocol with just a serial adapter and even though the large scale structure of the protocol is known too
  • even more detailed article
  • i did not find out what part of the protocol actually is proprietary and what not.

Difference between microcontroller and -processor

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