12012/03/30 - Mark Hatle <mark.hatle@windriver.com> 2 - Initial Revision 3 4 5Introduction 6============ 7The individual CPU, and ABI tunings are contained in this directory. A 8number of local and global variables are used to control the way the 9tunings are setup and how they work together to specify an optimized 10configuration. 11 12The following is brief summary of the generic components that are used 13in these tunings. 14 15AVAILTUNES - This is a list of all of the tuning definitions currently 16available in the system. Not all tunes in this list may be compatible 17with the machine configuration, or each other in a multilib 18configuration. Each tuning file can add to this list using "+=", but 19should never replace the list using "=". 20 21DEFAULTTUNE - This specifies the tune to use for a particular build. 22Each tune should specify a reasonable default, which can be overriden by 23a machine or multilib configuration. The specified tune must be listed 24in the AVAILTUNES. 25 26TUNEVALID[feature] - The <feature> is defined with a human readable 27explanation for what it does. All architectural, cpu, abi, etc tuning 28features must be defined using TUNEVALID. 29 30TUNECONFLICTS[feature] - A list of features which conflict with <feature>. 31New sanity checks will try to reject combinations in which a single 32tuning ends up with features which conflict with each other. 33 34TUNE_FEATURES - This is automatically defined as TUNE_FEATURES_tune-<tune>. 35See TUNE_FEATURES_tune-<tune> for more information. 36 37TUNE_FEATURES_tune-<tune> - Specify the features used to describe a 38specific tune. This is a list of features that a tune support, each 39feature must be in the TUNEVALID list. Note: the tune and a given 40feature name may be the same, but they have different purposes. Only 41features may be used to change behavior, while tunes are used to 42describe an overall set of features. 43 44ABIEXTENSION - An ABI extension may be specified by a specific feature 45or other tuning setting, such as TARGET_FPU. Any ABI extensions either 46need to be defined in the architectures base arch file, i.e. 47ABIEXTENSION = "eabi" in the arm case, or appended to in specific tune 48files with a ".=". Spaces are not allowed in this variable. 49 50TUNE_CCARGS - Setup the cflags based on the TUNE_FEATURES settings. 51These should be additive when defined using "+=". All items in this 52list should be dynamic! i.e. 53${@bb.utils.contains("TUNE_FEATURES", "feature", "cflag", "!cflag", d)} 54 55TUNE_ARCH - The GNU canonical arch for a specific architecture. i.e. 56arm, armeb, mips, mips64, etc. This value is used by bitbake to setup 57configure. TUNE_ARCH definitions are specific to a given architecture. 58They may be a single static definition, or may be dynamically adjusted. 59See each architecture's README for details for that CPU family. 60 61TUNE_PKGARCH - The package architecture used by the packaging systems to 62define the architecture, abi and tuning of a particular package. 63Similarly to TUNE_ARCH, the definition of TUNE_PKGARCH is specific to 64each architecture. See each architectures README for details for that 65CPU family. 66 67PACKAGE_EXTRA_ARCHS - Lists all runtime compatible package 68architectures. By default this is equal to 69PACKAGE_EXTRA_ARCHS_tune-<tune>. If an architecture deviates from the 70default it will be listed in the architecture README. 71 72PACKAGE_EXTRA_ARCHS_tune-<tune> - List all of the package architectures 73that are compatible with this specific tune. The package arch of this 74tune must be in the list. 75 76TARGET_FPU - The FPU setting for a given tune, hard (generate floating 77point instructions), soft (generate internal gcc calls), "other" 78architecture specific floating point. This is synchronized with the 79compiler and other toolchain items. This should be dynamically 80configured in the same way that TUNE_CCARGS is. 81 82BASE_LIB_tune-<tune> - The "/lib" location for a specific ABI. This is 83used in a multilib configuration to place the libraries in the correct, 84non-conflicting locations. 85 86 87Best Practice 88============= 89The tune infrastructure is designed to be hierarchical. When writing a 90new tune file for a "fast-forward" CPU architecture (one that supports 91everything from a previous generation), it is recommended to require the 92previous generation tune file and specify PACKAGE_EXTRA_ARCHS using the 93previous generation's override and appending the new tune. Note that 94only one previous tune file should be included to avoid mutiple includes 95of the base arch which could lead to a broken configuration due to 96multiple prepend and append assignments. 97 98For example, for x86, there is a common x86/arch-x86.inc which is 99included in the base i586 tune file. The core2 tune builds 100on that, and corei7 builds on core2. 101