8.43 --cpu=name

Enables code generation for the selected ARM® processor or architecture.

Syntax

--cpu=name

Where name is the name of a processor or architecture:

  • If name is the name of a processor, enter it as shown on ARM data sheets, for example, ARM7TDMI, ARM1176JZ-S, MPCore.

  • If name is the name of an architecture, it must belong to the list of architectures shown in the following table.

Processor and architecture names are not case-sensitive.

Wildcard characters are not accepted.

The following table shows the supported architectures. For a complete list of the supported architecture and processor names, specify the --cpu=list option.

Table 8-3 Supported ARM architectures

Architecture Description
4 ARMv4 without Thumb
4T ARMv4 with Thumb
5T ARMv5 with Thumb and interworking
5TE ARMv5 with Thumb, interworking, DSP multiply, and double-word instructions
5TEJ

ARMv5 with Thumb, interworking, DSP multiply, double-word instructions, and Jazelle® extensions

Note:

armcc cannot generate Java bytecodes.

6 ARMv6 with Thumb, interworking, DSP multiply, double-word instructions, unaligned and mixed-endian support, Jazelle, and media extensions.
6-M

ARMv6 microcontroller profile with Thumb only, plus processor state instructions.

6S-M

ARMv6 microcontroller profile with Thumb only, plus processor state instructions and OS extensions.

6K ARMv6 with SMP extensions.
6T2 ARMv6 with Thumb (Thumb-2 technology).
6Z ARMv6 with Security Extensions.
7 ARMv7 with Thumb (Thumb-2 technology) only, and without hardware divide.
7-A ARMv7 application profile.
7-A.security ARMv7-A architecture profile with the SMC instruction (formerly SMI).

7-R

ARMv7 real-time profile.

7-M ARMv7 microcontroller profile.
7E-M ARMv7-M architecture profile with DSP extension.

Note:

  • ARMv7 is not an actual ARM architecture. --cpu=7 denotes the features that are common to the ARMv7-A, ARMv7-R, and ARMv7-M architectures. By definition, any given feature used with --cpu=7 exists on the ARMv7-A, ARMv7-R, and ARMv7-M architectures.

  • 7-A.security is not an actual ARM architecture, but rather refers to 7-A plus Security Extensions.

  • The full list of supported architectures and processors depends on your license.

Default

armcc assumes --cpu=ARM7TDMI if you do not specify a --cpu option.

Usage

The following general points apply to processor and architecture options:

Processors
  • Selecting the processor selects the appropriate architecture, Floating-Point Unit (FPU), and memory organization.

  • The supported --cpu values include all current ARM product names or architecture versions.

    Other ARM architecture-based processors, such as the Marvell Feroceon and the Marvell XScale, are also supported.

  • If you specify a processor for the --cpu option, the generated code is optimized for that processor. This enables the compiler to use specific coprocessors or instruction scheduling for optimum performance.

Architectures
  • If you specify an architecture name for the --cpu option, the generated code can run on any processor supporting that architecture. For example, --cpu=5TE produces code that can be used by the ARM926EJ-S processor.

FPU
  • Some specifications of --cpu imply an --fpu selection.

    For example, when building with the --arm option, --cpu=ARM1136JF-S implies --fpu=vfpv2. Similarly, --cpu=Cortex-R4F implies --fpu=vfpv3_d16.

    Note:

    Any explicit FPU, set with --fpu on the command line, overrides an implicit FPU.
  • If no --fpu option is specified and no --cpu option is specified, --fpu=softvfp is used.

ARM/Thumb
  • Specifying a processor or architecture that supports Thumb instructions, such as --cpu=ARM7TDMI, does not make the compiler generate Thumb code. It only enables features of the processor to be used, such as long multiply. Use the --thumb option to generate Thumb code, unless the processor is a Thumb-only processor, for example Cortex-M4. In this case, --thumb is not required.

    Note:

    Specifying the target processor or architecture might make the generated object code incompatible with other ARM processors. For example, code generated for architecture ARMv6 might not run on an ARM920T processor, if the generated object code includes instructions specific to ARMv6. Therefore, you must choose the lowest common denominator processor suited to your purpose.
  • If you are building for mixed ARM/Thumb systems for processors that support ARMv4T or ARMv5T, then you must specify the interworking option --apcs=/interwork. By default, this is enabled for processors that support ARMv5T or above.

  • If you build for Thumb, that is with the --thumb option on the command line, the compiler generates as much of the code as possible using the Thumb instruction set. However, the compiler might generate ARM code for some parts of the compilation. For example, if you are generating code for a 16-bit Thumb processor and using VFP, any function containing floating-point operations is compiled for ARM.

  • If the architecture only supports Thumb, you do not have to specify --thumb on the command line. For example, if building for ARMv7-M with --cpu=7-M, you do not have to specify --thumb on the command line, because ARMv7-M only supports Thumb. Similarly, ARMv6-M and other Thumb-only architectures.

Restrictions

You cannot specify both a processor and an architecture on the same command-line.

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