ARC Toolchain Variants

The GCC toolchain has support for three ARC CPU families, namely

  • ARCompact (i.e., ARCv1) CPU family made of ARC6xx, and ARC7xx processors;

  • ARCv2 CPU family made of ARCEM, and ARCHS procesors;

  • ARCv3 CPU family made of ARC32:HS5x, and ARC64:HS6x processors.

Most of the above processors are 32bit RISC processors. Notable exception is ARC64:HS6x processors which is a 64bit RISC machine.

The next table depicts which GCC driver should be used depending on ARC CPU family.

ARC’s GCC driver/triplet name

Family

Driver/Triplet

Observations

ARCv1

arc-elf32-gcc

Specific CPU selected by -mcpu option

ARCv2

arc-elf32-gcc

Likewise

ARCv3

arc64-elf-gcc

Works for both 32b or 64b variants

ARCv1 and ARCv2 Toolchain

The GCC option -mcpu= for ARC does not only designate the ARC CPU family (ARC EM, HS, 600 or 700), but also enables the corresponding set of optional instructions defined for the selected configuration. Therefore a particular -mcpu value selects not only a family, but also other -m<something> GCC options for ARC.

Value of -mcpu= option not only sets various other -m<something> options to particular values, but also selects a specific standard library build which was done for this particular core configuration. It is possible to override selection of hardware extensions by passing individual -m<something> options to compiler after the -mcpu= option, however standard library build used for linkage still will be the one matching -mcpu= value. Therefore, for example, option combination -mcpu=em4 -mno-code-density will generate code that doesn’t use code density instructions, however it will be linked with standard library that has been built with just -mcpu=em4, which uses code density instructions - therefore final application still may use code density instructions. That’s why TCF generator, for example, analyzes hardware features present in the configured processor and selects -mcpu= value that is the best match for this configuration.

ARC EM

The following table summarize what options are set by each of the possible -mcpu values for ARC EM.

-mcpu values for ARC EM

-mcpu=

-mcode-density

-mnorm

-mswap

-mbarrel-shifter

-mdiv-rem

-mmpy-option

-mfpu

-mrf16

em

none

em_mini

none

Y

em4

Y

none

arcem

Y

Y

wlh1

em4_dmips

Y

Y

Y

Y

Y

wlh1

em4_fpus

Y

Y

Y

Y

Y

wlh1

fpus

em4_fpuda

Y

Y

Y

Y

Y

wlh1

fpuda

The above -mcpu values correspond to specific ARC EM Processor templates presented in the ARChitect tool. It should be noted however that some ARC features are not currently supported in the GNU toolchain, for example DSP instruction support, reduced register size and reduced register sets. Relationship between -mcpu values above and ARC EM Processor templates in ARChitect tool are limited to options listed in the table. Tables will be updated as support for more options get added to the GNU toolchain.

  • -mcpu=em doesn’t correspond to any specific template, it simply defines the base ARC EM configuration without any optional instructions.

  • -mcpu=em_mini is same as em, but uses reduced register file with only 16 core registers.

  • -mcpu=em4 is a base ARC EM core configuration with -mcode-density option. It corresponds to the following ARC EM templates in ARChitect: em4_mini, em4_sensor, em4_ecc, em6_mini, em5d_mini, em5d_mini_v3, em5d_nrg, em7d_nrg, em9d_mini. Note, however, that those mini templates has a reduced core register file, while this option doesn’t specify it.

  • -mcpu=arcem doesn’t correspond to any specific template, it is legacy flag preserved for compatibility with older GNU toolchain versions, where -mcpu used to select only a CPU family, while optional features were enabled or disable by individual -m<something> options.

  • -mcpu=em4_dmips is a full-featured ARC EM configuration for integer operations. It corresponds to the following ARC EM templates in ARChitect: em4_dmips, em4_rtos, em6_dmips, em4_dmips_v3, em4_parity, em6_dmips_v3, em6_gp, em5d_voice_audio, em5d_nrg_v3, em7d_nrg_v3, em7d_voice_audio, em9d_nrg, em9d_voice_audio, em11d_nrg and em11d_voice_audio.

  • -mcpu=em4_fpus is like em4_dmips but with additional support for single-precision floating point unit. It corresponds to the following ARC EM templates in ARChitect: em4_dmips_fpusp, em4_dmips_fpusp_v3, em5d_nrg_fpusp and em9d_nrg_fpusp.

  • -mcpu=em4_fpuda is like em4_fpus but with additional support for double-precision assist instructions. It corresponds to the following ARC EM templates in ARChitect: em4_dmips_fpuspdp and em4_dmips_fpuspdp_v3.

  • -mcpu=quarkse_em is a configuration for ARC processor in Intel Quark SE chip.

    Option

    quarkse_em

    -mcode-density

    Y

    -mnorm

    Y

    -mswap

    Y

    -mbarrel-shifter

    Y

    -mdiv-rem

    Y

    -mmpy-option

    wlh2

    -mfpu

    quark

    -mrf16

ARC HS

The following table summarize what options are set by each of the possible -mcpu values for ARC HS.

-mcpu values for ARC HS

-mcpu=

-mdiv-rem

-matomic

-mll64

-mmpy-option

-mfpu

hs

Y

none

hs34

Y

mpy

archs

Y

Y

Y

mpy

hs38

Y

Y

Y

plus_qmacw

hs4x

Y

Y

Y

plus_qmacw

hs4xd

Y

Y

Y

plus_qmacw

hs38_linux

Y

Y

Y

plus_qmacw

fpud_all

The above -mcpu values correspond to specific ARC HS Processor templates presented in the ARChitect tool. It should be noted however that some ARC features are not currently supported in the GNU toolchain, for example reduced register size and reduced register sets. Relationship between -mcpu values above and ARC HS Processor templates in ARChitect tool are limited to options listed in the table. Tables will be updated as support for more options get added to the GNU toolchain.

  • -mcpu=hs corresponds to a basic ARC HS with only atomic instructions enabled. It corresponds to the following ARC HS templates in ARChitect: hs34_base, hs36_base and hs38_base.

  • -mcpu=hs34 is like hs but with with additional support for standard hardware multiplier. It corresponds to the following ARC HS templates in ARChitect: hs34, hs36 and hs38.

  • -mcpu=archs is a generic CPU, which corresponds to the default configuration in older GNU toolchain versions.

  • -mcpu=hs38 is a fully featured ARC HS. It corresponds to the following ARC HS templates in ARChitect: hs38_full

  • -mcpu=hs4x and -mcpu=hs4xd have same option set as -mcpu=hs38 but compiler will optimize instruction scheduling for specified processors.

  • -mcpu=hs38_linux is a fully featured ARC HS with additional support for double-precision FPU.

ARC 600 and ARC 700

The following table summarize what options are set by each of the possible -mcpu values for ARC 600 and ARC 700.

-mcpu values for ARC 600 and ARC 700

-mcpu

-mnorm

-mswap

-mbarrel-shifter

multiplier

arc700

Y

Y

Y

-mmpy

arc600

Y

arc600_norm

Y

Y

arc600_mul64

Y

Y

-mmul64

arc600_mul32x16

Y

Y

-mmul32x16

arc601

arc601_norm

Y

arc601_mul64

Y

-mmul64

arc601_mul32x16

Y

-mmul32x16

ARCv3 Toolchain

The next -mcpu options are recognized by the ARC64 GCC compiler.

-mcpu variants for ARCv3

-mcpu

-msimd

-m128

-mll64

hs5x

Y

N.A.

N

hs58

Y

N.A.

Y

hs6x

Y

N

N.A.

hs68

Y

Y

N.A.

In baremetal, we provide a number of pre-build multilib libraries. These are:

Multilib configurations

Option

Observations

-mfpu=fpus

Single precision floating point, wide configuration on.

-mfpu=fpud

Single/Double precision FP, wide configuration on.

-m128

Using 128b load/store instructions. Alias for -mcpu=hs68

-mcpu=hs5x

For HS5x CPU processors class.

-mcpu=hs58

For HS58 CPU processors class.

Controlling the memory model

Memory models

-mcmodel

Memory size for Data/Code

small

1MB region.

medium

4GB region. Used by -fpic

large

Full memory. Used by -fPIC

Other tweaking options

Tweak options

Options

Good for …

-mfpmov

Reduces the pressure on GPRs by using FPRs for inline memory operations.

-mbrcc

Generate BRcc instructions early on. Good for size.

-mbbit

Likewise but for BBITx instructions.