ARM Cortex-M

ARM Cortex-M0 and Cortex-M3 microcontroller ICs from NXP and Silicon Labs (Energy Micro)
Die from a STM32F100C4T6B IC.
24 MHz ARM Cortex-M3 microcontroller with 16 KB flash memory, 4 KB RAM. Manufactured by STMicroelectronics.

The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by ARM Holdings for microcontroller use. The cores consist of the Cortex-M0, Cortex-M0+, Cortex-M1, Cortex-M3, Cortex-M4(F), Cortex-M7(F), Cortex-M23, Cortex-M33(F).[1][2][3][4][5][6][7] If the Cortex-M4 / M7 / M33 silicon has the FPU option, then the core is known as the Cortex-M4F / Cortex-M7F / Cortex-M33F. ARM Cortex-M cores have been shipped in tens of billions of devices.[8]

Overview

Announced
Year Core
2004 Cortex-M3
2007 Cortex-M1
2009 Cortex-M0
2010 Cortex-M4(F)
2012 Cortex-M0+
2014 Cortex-M7(F)
2016 Cortex-M23
2016 Cortex-M33(F)

The ARM Cortex-M family are ARM microprocessor cores which are designed for use in microcontrollers, ASICs, FPGAs, ASSPs, and SoC. Cortex-M cores are commonly used as dedicated microcontroller chips, but also are "hidden" inside of SoC chips as power management controllers, I/O controllers, system controllers, touch screen controllers, smart battery controllers, and sensors controllers.

Though 8-bit microcontrollers were very popular in the past, Cortex-M has slowly been chipping away at the 8-bit market as the prices of low-end Cortex-M chips have moved downward. Cortex-M have become a popular replacements for 8-bit chips in applications that benefit from 32-bit math operations, and replacing older legacy ARM cores such as ARM7 and ARM9.

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
ARM Core Cortex
M0[1] 		Cortex
M0+[2] 		Cortex
M1[3] 		Cortex
M3[4] 		Cortex
M4[5] 		Cortex
M7[6] 		Cortex
M23[7] 		Cortex
M33
SysTick 24-bit Timer Optional Optional Optional Yes Yes Yes Optional Optional
Single-cycle I/O port No Optional No No No No Optional Optional
Bit-Band memory No[12] No[12] No* Optional Optional No No No
Memory Protection
Unit (MPU) 		No Optional
(8) 		No Optional
(8) 		Optional
(8) 		Optional
(8,16) 		Optional
(4,8,12,16) 		Optional
Security Attribution
Unit (SAU) 		No No No No No No Optional
(4,8) 		Optional
Instruction TCM No No Optional No No Optional No Optional
Data TCM No No Optional No No Optional No Optional
Instruction Cache No[13] No[13] No[13] No[13] No[13] Optional No Optional
Data Cache No[13] No[13] No[13] No[13] No[13] Optional No Optional
Vector Table Offset
Register (VTOR) 		No Optional Optional Optional Optional Optional Optional Optional
Computer architecture Von Neumann Von Neumann Von Neumann Harvard Harvard Harvard Von Neumann Harvard

Additional silicon options:[9][10]

Instruction sets

The Cortex-M0 / M0+ / M1 implement the ARMv6-M architecture,[9] the Cortex-M3 implements the ARMv7-M architecture,[10] and the Cortex-M4 / M7 implements the ARMv7E-M architecture.[10] 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 / M33.[9][10] Only Thumb-1 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-1, some Thumb-2, including a 32-bit result multiply. The Cortex-M0 / M0+ / M1 / M23 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-1 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 / M33 have all base Thumb-1 and Thumb-2 instructions. The Cortex-M3 adds three Thumb-1 instructions, all Thumb-2 instructions, hardware integer 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).[9][10]

ARM Cortex-M instruction variations
ARM Core Cortex
M0[1] 		Cortex
M0+[2] 		Cortex
M1[3] 		Cortex
M3[4] 		Cortex
M4[5] 		Cortex
M7[6] 		Cortex
M23[7] 		Cortex
M33
Thumb-1 instructions Most Most Most Entire Entire Entire Most Entire
Thumb-2 instructions Some Some Some Entire Entire Entire Some Entire
Multiply instructions 32-bit result 32-bit result 32-bit result 32-bit result
64-bit result 		32-bit result
64-bit result 		32-bit result
64-bit result 		32-bit result 32-bit result
64-bit result
Divide instructions No No No Yes Yes Yes Yes Yes
Saturated instructions No No No Some Yes Yes No Yes
DSP instructions No No No No Yes Yes No Optional
Floating-point instructions No No No No Optional: SP Optional: SP
or SP & DP 		No Optional: SP
TrustZone instructions No No No No No No Optional Optional
Instruction pipeline 3 stages 2 stages 3 stages 3 stages 3 stages 6 stages 2 stages 3 stages
Computer architecture Von Neuman Von Neumann Von Neumann Harvard Harvard Harvard Von Neumann Harvard
ARM architecture ARMv6-M[9] ARMv6-M[9] ARMv6-M[9] ARMv7-M[10] ARMv7E-M[10] ARMv7E-M[10] ARMv8-M[14] ARMv8-M[14]
ARM Cortex-M instruction groups
Group Instr
bits 		Instructions Cortex
M0 		Cortex
M0+ 		Cortex
M1 		Cortex
M3 		Cortex
M4 		Cortex
M7 		Cortex
M23 		Cortex
M33
Thumb-1 16 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 Yes Yes Yes Yes Yes Yes Yes Yes
Thumb-1 16 CBNZ, CBZ No No No Yes Yes Yes Yes Yes
Thumb-1 16 IT No No No Yes Yes Yes No Yes
Thumb-2 32 BL, DMB, DSB, ISB, MRS, MSR Yes Yes Yes Yes Yes Yes Yes Yes
Thumb-2 32 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, SEV, SMLAL, SMULL, SSAT, STC, STMDB, STR, STRB, STRBT, STRD, STREX, STREXB, STREXH, STRH, STRHT, STRT, SUB, SXTB, SXTH, TBB, TBH, TEQ, TST, UBFX, UMLAL, UMULL, USAT, UXTB, UXTH, WFE, WFI, YIELD No No No Some Yes Yes No Yes
Thumb-2 32 SDIV, UDIV No No No Yes Yes Yes Yes Yes
DSP 32 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 No No No No Yes YesNo Optional
SP Float 32 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 No No No No Optional
SP FPU 		Optional
SP FPU 		No Optional
SP FPU
DP Float 32 VCVTA, VCVTM, VCVTN, VCVTP, VMAXNM, VMINNM, VRINTA, VRINTM, VRINTN, VRINTP, VRINTR, VRINTX, VRINTZ, VSEL No No No No No Optional
DP FPU 		No No
TrustZone 16 BLXNS, BXNS No No No No No No Optional Optional
TrustZone 32 SG, TT, TTT, TTA, TTAT No No No No No No Optional Optional

ARM deprecations

The ARM architecture for ARM Cortex-M series removed some features from older legacy cores:[9][10]

The capabilities of the 32-bit ARM instruction set is duplicated in many way by the Thumb-1 and Thumb-2 instruction sets, but some ARM features don't have a similar feature:

The 16-bit Thumb-1 instruction set has evolved over time since it was first released in the legacy ARM7T cores with the ARMv4T architecture. New Thumb-1 instructions were added as each legacy ARMv5 / ARMv6 / ARMv6T2 architectures were released. Some 16-bit Thumb-1 instructions were removed from the Cortex-M cores:

Cortex-M0

Cortex-M0
Instruction set Thumb-1 (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-1 (most),
Thumb-2 (some)
Microarchitecture ARMv6-M
NXP (Freescale) FRDM-KL25Z Board with KL25Z128VLK (Kinetis L)

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 the use of 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)[15]

Cortex-M1

Cortex-M1
Instruction set Thumb-1 (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 vendors support the Cortex-M1 as soft-cores on their FPGA chips:

Cortex-M3

Cortex-M3
Instruction set Thumb-1, Thumb-2,
Saturated (some)
Microarchitecture ARMv7-M
Arduino Due board with Atmel ATSAM3X8E (ARM Cortex-M3 core) microcontroller
NXP LPCXpresso Development Board with LPC1343

Key features of the Cortex-M3 core are:[4][16]

Silicon options:

Chips

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

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

The following FPGAs include a Cortex-M3 core:

Cortex-M4

Cortex-M4(F)
Instruction set Thumb-1, Thumb-2,
Saturated, DSP,
FPU (SP)
Microarchitecture ARMv7E-M
Silicon Labs (Energy Micro) Wonder Gecko STK Board with EFM32WG990
TI Stellaris Launchpad Board with LM4F120

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-1, Thumb-2,
Saturated, DSP,
FPU (SP & DP)
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.[19][20] 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:[6]

Silicon options:

Chips

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

Cortex-M23

Cortex-M23
Instruction set Thumb-1 (most),
Thumb-2 (some),
Divide, TrustZone
Microarchitecture ARMv8-M

The Cortex-M23 core was announced in October 2016[23] and based on the newer ARMv8-M architecture that was previously announced in November 2015.[24] Conceptually the Cortex-M23 is similar to a Cortex-M0+ plus integer divide instructions and TrustZone security features, and also has a 2-stage instruction pipeline.

As of July 2017, the "ARM Cortex-M23 ARM Generic User Guide" is not yet available from ARM Holdings, though the "ARM Cortex-M23 Technical Reference Manual" is available.

Key features of the Cortex-M23 core are:[7][23]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M23 core:

Cortex-M33

Cortex-M33(F)
Instruction set Thumb-1, Thumb-2,
Saturated, DSP,
FPU (SP), TrustZone
Microarchitecture ARMv8-M

The Cortex-M33 core was announced in October 2016[23] and based on the newer ARMv8-M architecture that was previously announced in November 2015.[24] Conceptually the Cortex-M33 is similar to a Cortex-M4 plus TrustZone security features, and also has a 3-stage instruction pipeline.

As of July 2017, the "ARM Cortex-M33 ARM Generic User Guide" is not yet available from ARM Holdings, though the "ARM Cortex-M33 Technical Reference Manual" is available.

Key features of the Cortex-M33 core are:[23]

Silicon options:

Chips

The following microcontrollers are based on the Cortex-M33 core:

Development tools

Segger J-Link PRO. Debug probe with SWD or JTAG interface to target ARM chip, and USB or Ethernet interfaces to host computer.

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 Cortex-M7 r0p2 Technical Reference Manual; ARM Holdings.
  7. 1 2 3 4 Cortex-M23 r1p0 Technical Reference Manual; ARM Holdings.
  8. ↑ ARM Cortex-M website; arm.com
  9. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ARMv6-M Architecture Reference Manual; ARM Holdings.
  10. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ARMv7-M Architecture Reference Manual; ARM Holdings.
  11. 1 2 3 4 Cortex-M3 Embedded Software Development; App Note 179; ARM Holdings.
  12. 1 2 3 Cortex-M System Design Kit; ARM Holdings.
  13. 1 2 3 4 5 6 7 8 9 10 ARM Cortex-M Programming Guide to Memory Barrier Instructions; Section 3.6 System implementation requirements; AppNote 321; arm.com
  14. 1 2 ARMv8-M Architecture Reference Manual; ARM Holdings.
  15. ↑ Fingas, Jon (25 February 2014). "Freescale makes the world's smallest ARM controller chip even tinier". Retrieved 2 October 2014.
  16. ↑ Sadasivan, Shyam. "An Introduction to the ARM Cortex-M3 Processor" (PDF). ARM Holdings. Archived from the original on July 26, 2014.
  17. ↑ http://datasheets.gpio.dk/dl/RTL8710%20wifi%20module%20specification.pdf#page=11
  18. ↑ "The Samsung Exynos 7420 Deep Dive - Inside A Modern 14nm SoC". AnandTech. Retrieved 2015-06-15.
  19. ↑ "Cortex-M7 Processor". ARM Holdings. Retrieved 2014-09-24.
  20. ↑ Press Release - ARM Supercharges MCU Market with High Performance Cortex-M7 Processor; arm.com; September 24, 2014;
  21. ↑ "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.
  22. ↑ "STM32 F7 series of very high performance MCUs with ARM® Cortex®-M7 core". STMicroelectronics. Retrieved 2014-09-24.
  23. 1 2 3 4 5 6 New ARM Cortex-M processors offer the next industry standard for secure IoT; ARM Holdings; October 25, 2016.
  24. 1 2 ARMv8-M Architecture Simplifies Security for Smart Embedded Devices; ARM Holdings; November 10, 2015.

Further reading

Wikimedia Commons has media related to ARM Cortex-M.
ARM Cortex-M official documents
ARM
Core 		Bit
Width 		ARM
Website 		ARM Generic
User Guide 		ARM Technical
Reference Manual 		ARM Architecture
Reference Manual
Cortex-M0 32 Link Link Link ARMv6-M
Cortex-M0+ 32 Link Link Link ARMv6-M
Cortex-M1 32 Link Link Link ARMv6-M
Cortex-M3 32 Link Link Link ARMv7-M
Cortex-M4(F) 32 Link Link Link ARMv7E-M
Cortex-M7(F) 32 Link Link Link ARMv7E-M
Cortex-M23 32 Link N/A Link ARMv8-M
Cortex-M33(F) 32 Link N/A Link ARMv8-M
Quick Reference Cards
Migrating
Other
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