Keil Logo Arm Logo

Technical Support

On-Line Manuals

Compiler Reference Guide

Conventions and Feedback Introduction Compiler Command-line Options -Aopt --allow_fpreg_for_nonfpdata, --no_allow_fpreg_for_ --allow_null_this, --no_allow_null_this --alternative_tokens, --no_alternative_tokens --anachronisms, --no_anachronisms --apcs=qualifer...qualifier --arm --arm_only --asm --asm_dir=directory_name --autoinline, --no_autoinline --bigend --bitband --brief_diagnostics, --no_brief_diagnostics --bss_threshold=num -c -C --c90 --c99 --code_gen, --no_code_gen --compatible=name --compile_all_input, --no_compile_all_input --conditionalize, --no_conditionalize --cpp --cpu=list --cpu=name --create_pch=filename -Dname[(parm-list)][=def] --data_reorder, --no_data_reorder --debug, --no_debug --debug_macros, --no_debug_macros --default_extension=ext --dep_name, --no_dep_name --depend=filename --depend_dir=directory_name --depend_format=string --depend_single_line, --no_depend_single_line --depend_system_headers, --no_depend_system_header --depend_target=target --diag_error=tag[,tag,...] --diag_remark=tag[,tag,...] --diag_style={arm|ide} --diag_suppress=tag[,tag,...] --diag_suppress=optimizations --diag_warning=tag[,tag,...] --diag_warning=optimizations --dollar, --no_dollar --dwarf2 --dwarf3 -E --echo --emit_frame_directives, --no_emit_frame_directive --enum_is_int --errors=filename --exceptions, --no_exceptions --exceptions_unwind, --no_exceptions_unwind --extended_initializers, --no_extended_initializer --feedback=filename --force_new_nothrow, --no_force_new_nothrow --forceinline --fp16_format=format --fpmode=model --fpu=list --fpu=name --friend_injection, --no_friend_injection -g --global_reg=reg_name[,reg_name,...] --guiding_decls, --no_guiding_decls --help -Idir[,dir,...] --ignore_missing_headers --implicit_include, --no_implicit_include --implicit_include_searches, --no_implicit_include --implicit_key_function, --no_implicit_key_functio --implicit_typename, --no_implicit_typename --info=totals --inline, --no_inline --interface_enums_are_32_bit --interleave -Jdir[,dir,...] --kandr_include -Lopt --library_interface=lib --library_type=lib --licretry --link_all_input, --no_link_all_input --list --list_dir=directory_name --list_macros --littleend --locale=lang_country --long_long --loose_implicit_cast --lower_ropi, --no_lower_ropi --lower_rwpi, --no_lower_rwpi --ltcg -M --md --message_locale=lang_country[.codepage] --min_array_alignment=opt --mm --multibyte_chars, --no_multibyte_chars --multifile, --no_multifile --multiply_latency=cycles --nonstd_qualifier_deduction, --no_nonstd_qualifie -o filename -Onum --old_specializations, --no_old_specializations --old_style_preprocessing --omf_browse -Ospace -Otime --output_dir=directory_name -P --parse_templates, --no_parse_templates --pch --pch_dir=dir --pch_messages, --no_pch_messages --pch_verbose, --no_pch_verbose --pending_instantiations=n --phony_targets --pointer_alignment=num --preinclude=filename --preprocess_assembly --preprocessed --protect_stack, --no_protect_stack --reassociate_saturation, --no_reassociate_saturat --reduce_paths, --no_reduce_paths --remarks --remove_unneeded_entities, --no_remove_unneeded_e --restrict, --no_restrict --retain=option --rtti, --no_rtti --rtti_data, --no_rtti_data -S --show_cmdline --signed_bitfields, --unsigned_bitfields --signed_chars, --unsigned_chars --split_ldm --split_sections --strict, --no_strict --strict_warnings --sys_include --thumb --trigraphs, --no_trigraphs --type_traits_helpers, --no_type_traits_helpers -Uname --unaligned_access, --no_unaligned_access --use_frame_pointer --use_pch=filename --using_std, --no_using_std --version_number --vfe, --no_vfe --via=filename --vla, --no_vla --vsn -W --wchar, --no_wchar --wchar16 --wchar32 --whole_program --wrap_diagnostics, --no_wrap_diagnostics Language Extensions Compiler-specific Features C and C++ Implementation Details Semihosting ARMv6 SIMD Instruction Intrinsics Via File Syntax Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Compiler Reference Guide

--bitband

--bitband

This option bit-bands all non const global structure objects. It enables a word of memory to be mapped to a single bit in the bit-band region. This enables efficient atomic access to single-bit values in SRAM and Peripheral regions of the memory architecture.

For peripherals that are width sensitive, byte, halfword, and word stores or loads to the alias space are generated for char, short, and int types of bitfields of bit-banded structs respectively.

Show/hideRestrictions

The following restrictions apply:

  • This option only affects struct types. Any union type or other aggregate type with a union as a member cannot be bit-banded.

  • Members of structs cannot be bit-banded individually.

  • Bit-banded accesses are generated only for single-bit bitfields.

  • Bit-banded accesses are not generated for const objects, pointers, and local objects.

  • Bit-banding is only available on some processors. For example, the Cortex-M4 and Cortex-M3 processors.

Show/hideExample

In Example 1 the writes to bitfields i and k are bit-banded when compiled using the --bitband command-line option.

Example 1. Bit-banding example

typedef struct {
  int i : 1;
  int j : 2;
  int k : 1;
} BB;

BB value;

void update_value(void)
{
  value.i = 1;
  value.k = 1;
}

Show/hideSee also

Copyright © 2007-2008, 2011-2012 ARM. All rights reserved.ARM DUI 0376D
Non-ConfidentialID062912

Keil logo

Arm logo
Important information

This site uses cookies to store information on your computer. By continuing to use our site, you consent to our cookies.