Understanding the Relationship Between STM32, Cortex-M3, and ARMv8-M

Reference: Wikipedia

Reference URL:

https://en.wikipedia.org/wiki/ARM_architecture

Everyone should know that STM32, Cortex-M3, and ARMv8-M are related to ARM, but may not be clear about their relationships or what they specifically are.

1. Overview

ARMv8-M: is a ARM architecture.

ARM architectures are divided into: ARMv1, ARMv2, …, ARMv8.

ARMv8 is divided into: ARMv8-A, ARMv8-R, ARMv8-M.

Cortex-M3: is an ARM processor core, which can also be understood as a member of the ARM processor family.

ARM processor cores are divided into: classic cores and Cortex cores.

Traditional cores: ARM7, ARM9, etc.

Cortex cores: Cortex-A, Cortex-R, Cortex-M, etc.

STM32: is an ARM core processor chip.

Most STM32s are Cortex-M cores, with a few containing Cortex-A7 (e.g., STM32MP).

As shown in the figure:

In fact, there are many more details to subdivide. In addition to these, there are some common topics, such as the ARM instruction set, Thumb-2 instruction set, etc.

The above is the overview, and below we will further describe some details.

2. Architecture

Since 1995, the “ARM Architecture Reference Manual” has been the main source of ARM documentation, providing details about ARM processor architecture and instruction sets, distinguishing interfaces, and the implementation details of all ARM processor support (such as instruction semantics) may vary. This architecture has evolved over time, and with the Cortex series cores, there are three configurations defined as follows:

“Application” configuration: Cortex-A series

“Embedded” configuration: Cortex-R series

“Microprocessor” configuration: ARM Cortex-M series.

Each configuration allows for its subset of architectures. For example, a subset ARMv7-M architecture (which supports fewer instructions) is used for the ARMv6-M configuration (used by Cortex M0/M0+/M1).

3. CPU Modes

At any given moment, the CPU can only be in one mode, but can switch modes due to external events (interrupts) or programming.

User Mode: Only non-privileged mode.

System Mode: Only privileged mode that does not require exceptions to enter. It can only be entered by executing instructions that explicitly write to the CPSR mode bits.

(svc) Mode: Privileged mode entered when the CPU is reset or the SWI instruction is executed.

Abort Mode: Privileged mode entered when prefetch abort or data abort exceptions occur.

Undefined Mode: Privileged mode entered when undefined instruction exceptions occur.

IRQ Mode: Privileged mode entered when the processor receives an IRQ interrupt.

Fast IRQ Mode: Privileged mode entered when the processor receives a fast IRQ interrupt.

Hyp Mode: Management mode introduced to provide hardware virtualization for the Cortex-A15 processor in armv-7a.

4. ARM Licensing

ARM does not manufacture or sell CPUs based on its designs but licenses its processor architectures to interested manufacturers.

The STM32 mentioned in the title is a processor produced by ST company that is licensed by ARM for the Cortex-M core.

ARM provides a variety of licensing terms, including pricing and distribution. For licensees, ARM provides integrated hardware descriptions of ARM cores, complete software development tools (compilers, debuggers, SDKs), and sales rights for silicon chips containing ARM CPUs.

Many semiconductor companies hold ARM licenses: Atmel, ST, NXP, TI, IBM, etc.

In the intellectual property industry, ARM is one of the most well-known and expensive CPU cores. A single customer product containing a basic ARM core may require a one-time licensing fee of up to $200,000. If it involves extensive architectural modifications, the cost can exceed ten million dollars.

5. ARM Core Timeline

The classic ARM7 was released as early as 1993, leading up to the Cortex-A series processors we see today.

In fact, there were some related processors before the ARM7, and interested friends can look up more information online.

Disclaimer:This article is sourced from Wikipedia, copyright belongs to the original author. If there are copyright issues, please contact me for removal.

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