Microcontrollers and boards

Reminder - Computer architecture

  • Main memory: RAM (see further)
  • Secondary memory:
    • hard drive
    • SSD (Flash)
  • I/O interfaces: for keyboard(s), mouse/mice, monitor(s), printer(s), network(s), etc.
  • When multiple CPUs: more complicated
RAM: Random Access Memory
SSD: Solid State Drive

Example - IBM z16 A01

  • 4 cabinets, each measuring approximately 48 x 185 cm
  • Maximum memory: 40 TB
CPC: Central Processor Complex
Source: IBM

Example - Desktop PC

Source: PB

Example - BeagleBone Black SBC

SBC: Single Board Computer
Source: beagleboard.org
  • The BeagleBone Black can be used as a general purpose computer
  • It can also be used as an embedded system
  • ⇒The definition in the previous section should not be taken strictly

Many different SBCs exist.

Continuing with integration

  • What about an Integrated Circuit (IC) containing one (or more) CPU(s), some memory, and I/O interfaces?
  • This is a microcontroller (MCU - MicroController Unit)

Microcontroller architecture

  • Some microcontrollers may have one or more caches
  • No more primary/secondary memory but RAM/Flash (see further) instead

Microprocessor vs microcontroller

  • A microprocessor (MPU - MicroProcessor Unit) contains one (or more) CPU(s) and some I/O interfaces
  • Most computers are based on microprocessors.

Reminder - Memory content retention

  • RAM is volatile memory: content is lost when the system is turned off
  • Flash is non-volatile memory
  • You may find other acronyms: ROM, PROM, EPROM, EEPROM, FRAM, MRAM, etc.
RAM: Random Access Memory - ROM: Read-Only Memory - PROM: Programmable ROM - EPROM: Erasable Programmable ROM - EEPROM: Electrically Erasable ROM - FRAM: Ferroelectric RAM - Magnetoresistive RAM

Important: flash memory can only accept a limited number of writes.

  • Depending on memory type: between 10,000 and 1 million writes
  • Wear-leveling algorithms: spread out write operations

Microcontroller architecture - more details

  • I/O interfaces: different types (see further)
  • Peripherals may be included (see further)
  • Energy management: on low power consumption microcontrollers

Embedded system

  • Printed Circuit Board (PCB)
  • A microcontroller
  • Additional elements (see next diagram)
  • Case

The name device is also used.

Board architecture

Energy management:

  • Voltage regulator
  • Protection against voltage inversion
  • Battery management system
  • Etc.

Wireless interface:

  • May be provided by the MCU

Data storage:

  • To store large amounts of data

Firmware storage:

  • To implement Over-The-Air (OTA) update

Example - EFR32BG24 Dev Kit

Important board/microcontroller characteristics?

  • Depend on the target application!
  • Example of characteristics to consider:
    • Extensions and/or libraries for ML support
    • Serial interfaces
    • Digital interfaces
    • Analog interfaces
    • Integrated wireless communication
    • Instruction cycle time
    • Memory (size, type, expandable or not)
    • Registers size (8/16/32 bits)
    • Packaging
    • etc.

Other important characteristics: hardware tools

  • Development board
  • Programmer, debugger
  • Open source hardware

Other important characteristics: software tools

  • Cross-compilation toolchain
  • Integrated Development Environment (IDE)
  • Open source software

Other important characteristics: support

  • Professional support
  • Active community (forums, examples...)

Some common microcontroller families

Arm

  • UK company created in 1990
  • There isn't any Arm microcontroller
  • Arm provides Intellectual Property (IP) blocks, under a licensing agreement
  • Among these blocks: RISC microcontrollers cores
  • Low power, low cost: Cortex-M family
RISC: Reduced Instruction Set Computer

325 billions of Arm-based chips shipped.

Source: Arm

Some Cortex-M licensees:

Cortex-M

Source: Arm

Facilities for ML applications on Cortex-M

  • Software library: CMSIS-NN - open-source library maximizing NN performance
  • Hardware extension: FPU
  • Hardware extension: DSP
  • Hardware extension: Helium - vector extension
  • Hardware extension: Ethos-U55 - NPU
CMSIS-NN: Common Microcontroller Software Interface Standard - Neural Network
FPU: Floating-Point Unit
DSP: Digital Signal Processing
NPU: Neural Processing Unit

Example: STMicroelectronics - STM32 family

Source: STMicroelectronics

STM32L073RZ

Source: STMicroelectronics
Source: STMicroelectronics
  • Price: US$6.95 (unit) - US$2.66 (10,000)
Development board

Price: US$16

Source: STMicroelectronics

STM32WL55

Source: STMicroelectronics
Source: STMicroelectronics
  • Price: US$7.75 (unit) - US$4.54 (10,000)
Development board

US$53

Source: STMicroelectronics

STM32N6 series

Source: STMicroelectronics
Development board

US$78

Source: STMicroelectronics

Example: Silicon Labs - EFR32 family

Source: Silicon Labs Wireless SoCs
  • Bluetooth: EFR32BG21, EFR32BG22, EFR32BG24, EFR32BG26, EFR32BG27
  • Wi-Fi: SiWx915, SiWx917, RS9116, WF200
  • Thread: EFR32MG12, EFR32MG13, EFR32MG21, EFR32MG24
  • Etc.

EFR32MG24

Source: EFR32MG24 Datasheet

Matrix Vector Processor (MVP) - hardware accelerator for (complex) vector and matrix operations.

The MVP Math Library provides the associated API.

API: Application Programming Interface
  • Price: around US$7 (unit)
Development board

US$79

Source: xG24 Dev Kit User's Guide

Espressif - ESP family

Espressif family

  • ESP32-P Series - high-power RISC-V dual-core + low-power single-core
  • ESP32-S Series - Xtensa LX7 dual-cor or single-core - Wi-Fi, BLE
  • ESP32-C Series - RISC-V dual-core or single-core - Wi-Fi (2.4 GHz / 5 GHz), BLE, IEEE 802.15.4
  • ESP32-H Series - RISC-V single-core
  • ESP32 Series - Xtensa LX6 dual-core or single-core - Wi-Fi, Bluetooth, BLE
BLE: Bluetooth Low Energy
IEEE 802.15.4: physical layer and MAC layer for Zigbee, 6LowPAN, Thread, Matter, etc.
Source: Espressif

A note about RISC-V

RISC-V is an open, royalty-free instruction set architecture (ISA).

The RISC-V International Association drives the development of RISC-V.

ESP32-C6FH4

Source: ESP32-C6 Datasheet

Some of the features

  • High-power RISC-V processor - clock up to 160 MHz
  • Low-power RISC-V processor - clock up to 20 MHz
  • L1 cache: 32 KB
  • ROM: 320 KB
  • Hig-power SRAM: 512 KB
  • Low-power SRAM: 16 KB
  • Flash: 4 MB
  • Price: US$2.05
Development board
Source: ESP32-C6-DevKitM-1
  • Price: US$7.96

For ML

ESP32-S3: vector instructions - ESP-DSP and ESP-NN libraries

ESP32-P4: instruction extensions (vector, complex, etc.)