ARM Cortex-M

ARM Cortex-M0 and Cortex-M3 ICs from NXP and Energy Micro
Die of a STM32F100C4T6B ARM Cortex-M3 microcontroller with 16 KB flash memory, 24 MHz CPU, motor control, and CEC functions. Manufactured by STMicroelectronics.

The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by ARM Holdings. The cores are intended for microcontroller use, and consist of the Cortex-M0, M0+, M1, M3, M4, and M7.[1][2][3][4][5]

Overview

Announced
Year Core
2004 Cortex-M3
2007 Cortex-M1
2009 Cortex-M0
2010 Cortex-M4
2012 Cortex-M0+
2014 Cortex-M7

ARM license

ARM Holdings neither manufactures nor sells CPU devices based on its own designs, but rather licenses the processor architecture to interested parties. ARM offers a variety of licensing terms, varying in cost and deliverables. To all licensees, ARM provides an integratable hardware description of the ARM core, as well as complete software development toolset and the right to sell manufactured silicon containing the ARM CPU.

Silicon customization

Integrated device manufacturers (IDM) receive the ARM Processor IP as synthesizable RTL (written in Verilog). In this form, they have the ability to perform architectural level optimizations and extensions. This allows the manufacturer to achieve custom design goals, such as higher clock speed, very low power consumption, instruction set extensions, optimizations for size, debug support, etc. To determine which components have been included in a particular ARM CPU chip, consult the manufacturer datasheet and related documentation.

Some of the most important options for the Cortex-M cores are:

ARM Cortex-M optional components[6][7]
ARM
Cortex-M 		SysTick
Timer 		Bit-
banding 		Memory Protection
Unit (MPU) 		Tightly-Coupled
Memory (TCM) 		CPU
cache 		Memory
architecture 		ARM
architecture
Cortex-M0[1]
Optional*
Optional[9]
No No No[10]
Von Neumann
ARMv6-M
Cortex-M0+[2]
Optional*
Optional[9]
Optional (8)
No No
Von Neumann
ARMv6-M
Cortex-M1[3]
Optional
Optional
No
Optional
No
Von Neumann
ARMv6-M
Cortex-M3[4]
Yes
Optional*
Optional (8)
No No
Harvard
ARMv7-M
Cortex-M4[5]
Yes
Optional*
Optional (8)
No  Possible[11]
Harvard
ARMv7E-M
Cortex-M7
Yes No
Optional (8 or 16)
Optional
Optional
Harvard
ARMv7E-M

Additional silicon options:[6][7]

Instruction sets

The Cortex-M0 / M0+ / M1 implement the ARMv6-M architecture,[6] the Cortex-M3 implements the ARMv7-M architecture,[7] and the Cortex-M4 / M7 implements the ARMv7E-M architecture.[7] The architectures are binary instruction upward compatible from ARMv6-M to ARMv7-M to ARMv7E-M. Binary instructions available for the Cortex-M0 / M0+ / M1 can execute without modification on the Cortex-M3 / M4 / M7. Binary instructions available for the Cortex-M3 can execute without modification on the Cortex-M4 / M7.[6][7] Only Thumb and Thumb-2 instruction sets are supported in Cortex-M architectures, but the legacy 32-bit ARM instruction set isn't supported.

All six Cortex-M cores implement a common subset of instructions that consists of most Thumb, some Thumb-2, including a 32-bit result multiply. The Cortex-M0 / M0+ / M1 were designed to create the smallest silicon die, thus having the fewest instructions of the Cortex-M family.

The Cortex-M0 / M0+ / M1 include Thumb instructions, except new instructions (CBZ, CBNZ, IT) which were added in ARMv7-M architecture. The Cortex-M0 / M0+ / M1 include a minor subset of Thumb-2 instructions (BL, DMB, DSB, ISB, MRS, MSR). The Cortex-M3 / M4 / M7 have all base Thumb and Thumb-2 instructions. The Cortex-M3 adds 3 Thumb instructions, all Thumb-2 instructions, hardware divide, and saturation arithmetic instructions. The Cortex-M4 adds DSP instructions and an optional single-precision floating-point unit (VFPv4-SP). The Cortex-M7 adds an optional double-precision FPU (VFPv5).[6][7]

ARM Cortex-M instruction variations[6][7]
ARM
Cortex-M 		Thumb Thumb-2 Hardware
multiply 		Hardware
divide 		Saturated
math 		DSP
extensions 		Floating-Point
Unit (FPU) 		ARM
architecture
Cortex-M0[1]
Most
Some
32-bit result
No No No No
ARMv6-M
Cortex-M0+[2]
Most
Some
32-bit result
No No No No
ARMv6-M
Cortex-M1[3]
Most
Some
32-bit result
No No No No
ARMv6-M
Cortex-M3[4]
Entire Entire 32 or 64-bit result Yes Yes No No
ARMv7-M
Cortex-M4[5]
Entire Entire 32 or 64-bit result Yes Yes Yes
Optional: SP
ARMv7E-M
Cortex-M7
Entire Entire 32 or 64-bit result Yes Yes Yes
Optional: SP
or SP & DP
ARMv7E-M
ARM Cortex-M instruction groups
Instructions Instruction
size 		Cortex
M0 		Cortex
M0+ 		Cortex
M1 		Cortex
M3 		Cortex
M4 		Cortex
M7
ADC, ADD, ADR, AND, ASR, B, BIC, BKPT, BLX, BX, CMN, CMP, CPS, EOR, LDM, LDR, LDRB, LDRH, LDRSB, LDRSH, LSL, LSR, MOV, MUL, MVN, NOP, ORR, POP, PUSH, REV, REV16, REVSH, ROR, RSB, SBC, SEV, STM, STMIA, STR, STRB, STRH, SUB, SVC, SXTB, SXTH, TST, UXTB, UXTH, WFE, WFI, YIELD
16-bit
Yes Yes Yes Yes Yes Yes
BL, DMB, DSB, ISB, MRS, MSR
32-bit
Yes Yes Yes Yes Yes Yes
CBNZ, CBZ, IT
16-bit
No No No Yes Yes Yes
ADC, ADD, ADR, AND, ASR, B, BFC, BFI, BIC, CDP, CLREX, CLZ, CMN, CMP, DBG, EOR, LDC, LDMA, LDMDB, LDR, LDRB, LDRBT, LDRD, LDREX, LDREXB, LDREXH, LDRH, LDRHT, LDRSB, LDRSBT, LDRSHT, LDRSH, LDRT, MCR, LSL, LSR, MLS, MCRR, MLA, MOV, MOVT, MRC, MRRC, MUL, MVN, NOP, ORN, ORR, PLD, PLDW, PLI, POP, PUSH, RBIT, REV, REV16, REVSH, ROR, RRX, RSB, SBC, SBFX, SDIV, SEV, SMLAL, SMULL, SSAT, STC, STMDB, STR, STRB, STRBT, STRD, STREX, STREXB, STREXH, STRH, STRHT, STRT, SUB, SXTB, SXTH, TBB, TBH, TEQ, TST, UBFX, UDIV, UMLAL, UMULL, USAT, UXTB, UXTH, WFE, WFI, YIELD
32-bit
No No No Yes Yes Yes
PKH, QADD, QADD16, QADD8, QASX, QDADD, QDSUB, QSAX, QSUB, QSUB16, QSUB8, SADD16, SADD8, SASX, SEL, SHADD16, SHADD8, SHASX, SHSAX, SHSUB16, SHSUB8, SMLABB, SMLABT, SMLATB, SMLATT, SMLAD, SMLALBB, SMLALBT, SMLALTB, SMLALTT, SMLALD, SMLAWB, SMLAWT, SMLSD, SMLSLD, SMMLA, SMMLS, SMMUL, SMUAD, SMULBB, SMULBT, SMULTT, SMULTB, SMULWT, SMULWB, SMUSD, SSAT16, SSAX, SSUB16, SSUB8, SXTAB, SXTAB16, SXTAH, SXTB16, UADD16, UADD8, UASX, UHADD16, UHADD8, UHASX, UHSAX, UHSUB16, UHSUB8, UMAAL, UQADD16, UQADD8, UQASX, UQSAX, UQSUB16, UQSUB8, USAD8, USADA8, USAT16, USAX, USUB16, USUB8, UXTAB, UXTAB16, UXTAH, UXTB16
32-bit
No No No No Yes Yes
VABS, VADD, VCMP, VCMPE, VCVT, VCVTR, VDIV, VLDM, VLDR, VMLA, VMLS, VMOV, VMRS, VMSR, VMUL, VNEG, VNMLA, VNMLS, VNMUL, VPOP, VPUSH, VSQRT, VSTM, VSTR, VSUB
32-bit
No No No No
Optional
SP FPU
Optional
SP FPU
14 new instructions for double-precision FPU (need to be added here)
32-bit
No No No No No
Optional
DP FPU

ARM deprecations

The ARM architecture for ARM Cortex-M series removed some features from older legacy cores:[6][7]

The capabilities of the 32-bit ARM instruction set is duplicated in many way by the Thumb and Thumb-2 instruction sets, but some ARM features don't have a similar feature:

The 16-bit Thumb instruction set has evolved over time since it was first released in the legacy ARM7T cores with the ARMv4T architecture. New Thumb instructions were added as each legacy ARMv5 / ARMv6 / ARMv6T2 architectures were released. Some 16-bit Thumb instructions were removed from the Cortex-M cores:

Cortex-M0

Cortex-M0
Instruction set Thumb (most),
Thumb-2 (some)
Microarchitecture ARMv6-M

The Cortex-M0 core is optimized for small silicon die size and use in the lowest price chips.

Key features of the Cortex-M0 core are:[1]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M0 core:

The following chips have a Cortex-M0 as a secondary core:

Cortex-M0+

Cortex-M0+
Instruction set Thumb (most),
Thumb-2 (some)
Microarchitecture ARMv6-M
Freescale FRDM-KL25Z Board with KL25Z128VLK (Kinetis L series)

The Cortex-M0+ is an optimized superset of the Cortex-M0. The Cortex-M0+ has complete instruction set compatibility with the Cortex-M0 thus allowing one to use the same compiler and debug tools. The Cortex-M0+ pipeline was reduced from 3 to 2 stages, which lowers the power usage. In addition to debug features in the existing Cortex-M0, a silicon option can be added to the Cortex-M0+ called the Micro Trace Buffer (MTB) which provides a simple instruction trace buffer. The Cortex-M0+ also received Cortex-M3 and Cortex-M4 features, which can be added as silicon options, such as the memory protection unit (MPU) and the vector table relocation.[2]

Key features of the Cortex-M0+ core are:[2]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M0+ core:


Smallest ARM microcontrollers are of the Cortex-M0+ type (as of 2014, smallest at 1.6 mm by 2 mm is Kinetis KL03)[12]

Cortex-M1

Cortex-M1
Instruction set Thumb (most),
Thumb-2 (some)
Microarchitecture ARMv6-M

The Cortex-M1 is an optimized core especially designed to be loaded into FPGA chips.

Key features of the Cortex-M1 core are:[3]

Silicon options:

Chips

The following FPGA vendors support the Cortex-M1 as soft-cores:

Cortex-M3

Cortex-M3
Instruction set Thumb, Thumb-2,
Saturated Math
Microarchitecture ARMv7-M
NXP LPCXpresso Development Board with LPC1343
mbed Board with NXP LPC1768
The TI Ducati SIP core uses a Cortex-M3 cores to offload video acceleration and image processing.

Key features of the Cortex-M3 core are:[4][13]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M3 core:

The following chips have a Cortex-M3 as a secondary core:

Cortex-M4

Cortex-M4(F)
Instruction set Thumb, Thumb-2,
Saturated Math, DSP,
FPU (SP) (M4F)
Microarchitecture ARMv7E-M
Energy Micro Wonder Gecko STK Board with EFM32WG990
TI Stellaris Launchpad Board with LM4F120
Tiva-C LaunchPad Module

Conceptually the Cortex-M4 is a Cortex-M3 plus DSP Instructions, and optional floating-point unit (FPU). If a core contains an FPU, it is known as a Cortex-M4F, otherwise it is a Cortex-M4.

Key features of the Cortex-M4 core are:[5]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M4 core:

The following microcontrollers are based on the Cortex-M4F (M4 + FPU) core:

The following chips have either a Cortex-M4 or M4F as a secondary core:

Cortex-M7

Cortex-M7(F)
Instruction set Thumb, Thumb-2,
Saturated Math, DSP,
FPU (SP & DP) (M7F)
Microarchitecture ARMv7E-M

The Cortex-M7 is a high-performance core with almost double the power efficiency of the older Cortex-M4. It features a 6-stage superscalar pipeline with branch prediction and an optional floating-point unit capable of single-precision and optionally double-precision operations.[15][16] The instruction and data buses have been enlarged to 64-bit wide over the previous 32-bit buses. If a core contains an FPU, it is known as a Cortex-M7F, otherwise it is a Cortex-M7.

Key features of the Cortex-M7 core are:

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M7 core:

Development tools

Segger J-Link EDU. JTAG/SWD debug probe for ARM microcontrollers with USB interface to host. Low price model for educational and home users.

Documentation

The amount of documentation for all ARM chips is daunting, especially for newcomers. The documentation for microcontrollers from past decades would easily be inclusive in a single document, but as chips have evolved so has the documentation grown. The total documentation is especially hard to grasp for all ARM chips since it consists of documents from the IC manufacturer and documents from CPU core vendor (ARM Holdings).

A typical top-down documentation tree is: manufacturer website, manufacturer marketing slides, manufacturer datasheet for the exact physical chip, manufacturer detailed reference manual that describes common peripherals and aspects of a physical chip family, ARM core generic user guide, ARM core technical reference manual, ARM architecture reference manual that describes the instruction set(s).

Documentation tree (top to bottom)
  1. IC manufacturer website
  2. IC manufacturer marketing slides
  3. IC manufacturer datasheet
  4. IC manufacturer reference manual
  5. ARM core website
  6. ARM core generic user guide
  7. ARM core technical reference manual
  8. ARM architecture reference manual

IC manufacturers have additional documents, such as: evaluation board user manuals, application notes, getting started guides, software library documents, errata, and more. See External Links section for links to official ARM documents.

See also

References

  1. 1 2 3 4 Cortex-M0 r0p0 Technical Reference Manual; ARM Holdings.
  2. 1 2 3 4 5 Cortex-M0+ r0p0 Technical Reference Manual; ARM Holdings.
  3. 1 2 3 4 Cortex-M1 r1p0 Technical Reference Manual; ARM Holdings.
  4. 1 2 3 4 Cortex-M3 r2p1 Technical Reference Manual; ARM Holdings.
  5. 1 2 3 4 Cortex-M4 r0p1 Technical Reference Manual; ARM Holdings.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ARMv6-M Architecture Reference Manual; ARM Holdings.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 ARMv7-M Architecture Reference Manual; ARM Holdings.
  8. 1 2 3 4 Cortex-M3 Embedded Software Development; App Note 179; ARM Holdings.
  9. 1 2 3 Cortex-M System Design Kit; ARM Holdings.
  10. ↑ http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0321a/BIHEADII.html
  11. ↑ K60 Family Product Brief; Freescale; May 2011.
  12. ↑ Fingas, Jon (25 February 2014). "Freescale makes the world's smallest ARM controller chip even tinier". Retrieved 2 October 2014.
  13. ↑ Sadasivan, Shyam. "An Introduction to the ARM Cortex-M3 Processor" (PDF). ARM Holdings.
  14. ↑ "The Samsung Exynos 7420 Deep Dive - Inside A Modern 14nm SoC". AnandTech. Retrieved 2015-06-15.
  15. ↑ "Cortex-M7 Processor". ARM Holdings. Retrieved 2014-09-24.
  16. ↑ Press Release - ARM Supercharges MCU Market with High Performance Cortex-M7 Processor; arm.com; September 24, 2014;
  17. ↑ "KV5x: Kinetis KV5x - 240 MHz, ARM® Cortex®-M7, Real-Time Control, Ethernet, Motor Control and Power Conversion, High-Performance Microcontrollers (MCUs)". Freescale Semiconductor. Retrieved 2015-04-09.
  18. ↑ "STM32 F7 series of very high performance MCUs with ARM® Cortex®-M7 core". STMicroelectronics. Retrieved 2014-09-24.

Further reading

External links

Wikimedia Commons has media related to ARM Cortex-M.
ARM Cortex-M official documents
ARM
Core 		ARM
Website 		ARM Generic
User Guide 		ARM Technical
Reference Manual 		ARM Architecture
Reference Manual
Cortex-M0
Link
Link
Link
ARMv6-M
Cortex-M0+
Link
Link
Link
ARMv6-M
Cortex-M1
Link
Link
Link
ARMv6-M
Cortex-M3
Link
Link
Link
ARMv7-M
Cortex-M4
Link
Link
Link
ARMv7E-M
Cortex-M7
Link
TBD
Link
ARMv7E-M
Quick Reference Cards
Migrating
Other
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