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Introduce initial Bazel build (#1705)
* Build boot_stage2 with Bazel Introduces the initial foundations of a Bazel build, including a toolchain, critical generated headers, platform patterns, and enough BUILD files to build boot_stage2. * Bazel libraries to support picotool * Move SDK defines to toolchain * Switch to `archive_override` in MODULE.bazel Uses archive_override where applicable to allow transitive bzlmod deps to propagate. * Multiplatform objcopy selection in Bazel build Makes an objcopy alias that redirects to the objcopy tool for the current exec platform, which allows boot_stage2 to build on Linux, macOS, and Windows. * Generate Bazel build files Adds initial set of generated Bazel build files. Note that these do not yet build, as dependency cycles are present. * Fix dependency cycles in Bazel build Fixes many dependency cycles, some were unintentionally created by the build file generator, others are true dependency cycles that require manual workarounds. * Silence warning in pico_stdio Bazel build Silences a stray warning in the Bazel build. * Fix wildcard Bazel build This makes `bazel build //...` succeed, and also prevents the fetching of toolchains that aren't compatible with the current execution environment (i.e. Windows computers will no longer try to download macOS toolchains). * Get the SDK working Finishes out the remainder of the work required to successfully compile a working blinky example. * Fix UART stdio dependencies in Bazel build Fixes some dependencies around pico_stdlib so that pico_stdlib links properly and UART stdio works. * Add linux support to Bazel build * Get Bazel deps from registry Adds external an external registry for resolving Bazel module dependencies. * Fix host configuration for picotool Provides the appropriate defines for host builds to support the picotool build. * Remove -ffreestanding from Bazel toolchain The -ffreestanding toolchain flag is quite strict, so remove it from the Bazel toolchain. * Remove unused .bzl file * Reduce Bazel compiler flags Cuts out most of the Bazel toolchain flags and only specifies the bare-minimum set of flags. Also, adds wrapper linker flags for functions the SDK wraps. * Get USB serial working Adds initial TinyUSB support and enough integration to get USB serial working. * Remove "Generated build file" Removes comments that indicates BUILD.bazel files are generated. This was used during initial bringup to indicate hand-crafted vs automatically generated BUILD.bazel files. * Do not build USB libraries unless configured Prevents USB libraries from being built unless the build is properly configured to use them. * Switch to rules_cc toolchains Moves toolchain configuration to use the new rules in rules_cc. * Minor cleanup in parse_version.py Cleans up trailing whitespace and runs the black formatter on parse_version.py. * Simplify constraint dimensions in Bazel build Consolidates the class/chip constraint settings to be a single constraint_setting with a config_setting that represents the rp2 class. * Update pin of rules_cc in Bazel build Includes a necessary fix for the target_compatible_with expression in the cc_toolchain to work as intended. * Move toolchains from pico.bzl to BUILD.bazel Moves toolchain definitions from pico.bzl to BUILD.bazel to make them easier to find and read. * Run buildifier on Bazel build files Fix trivial formatting issues by running buildifier on all BUILD.bazel files. * Make objcopy rule Makes a simple objcopy rule to remove direct references to the ARM toolchains. * Fix link flags in Bazel build Critical flags were not being applied to link steps. This applies -mcpu and -mthumb to the link steps to make the produced binaries work again. * Mention missing host build support * Fix various Bazel library rules * pico_bit_ops was incomplete. * pico_double and pico_float were trying to link in the "none" implementation. * Extend Bazel build documentation Improves documentation and comments across the Bazel build. * Clean up auxilary tools in Bazel build Switches genrules to use skylib rules to simplify things. Reworks version header generation to use the Bazel module version rather than parsing CMake. * Update boot_stage2 Bazel build file Moves `includes` to be enumerated on the correct library. * Add WORKSPACE version fallback WORKSPACE Bazel projects don't support querying module version, so add a fallback of '0.0.1-WORKSPACE' so the build can succeed. * Fix malloc handling in Bazel build * Fix Bazel dependency cycle in pico_malloc * Prevent malloc from being linked into boot_stage2 Prevents Bazel from ever trying to link malloc into the boot_stage2 binary. * Remove custom bootloader platform A dedicated boot_stage2 platform introduces a lot of complexity that needs to be more thought-through.
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‎.bazelrc

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# Required for new toolchain resolution API.
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build --incompatible_enable_cc_toolchain_resolution
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build --@rules_cc//cc/toolchains:experimental_enable_rule_based_toolchains
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# Produce useful output when the build fails.
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common --verbose_failures

‎.bazelversion

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7.0.2

‎.gitignore

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cmake-*
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.DS_Store
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build
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bazel-*
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# Ignore until https://github.com/bazelbuild/bazel/issues/20369 is fixed.
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MODULE.bazel.lock

‎BUILD.bazel

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‎MODULE.bazel

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module(name = "pico-sdk", version = "1.6.0-rc1")
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bazel_dep(name = "platforms", version = "0.0.8")
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bazel_dep(name = "bazel_skylib", version = "1.6.1")
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# Note: rules_cc is special-cased repository; a dependency on rules_cc in a
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# module will not ensure that the root Bazel module has that same version of
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# rules_cc. For that reason, this primarily acts as a FYI. You'll still need
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# to explicitly list this dependency in your own project's MODULE.bazel file.
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bazel_dep(name = "rules_cc", version = "0.0.10")
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# rules_cc v0.0.10 is not yet cut, so manually pull in the desired version.
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# This does not apply to dependent projects, so it needs to be copied to your
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# project's MODULE.bazel too.
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archive_override(
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module_name = "rules_cc",
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urls = "https://github.com/bazelbuild/rules_cc/archive/1acf5213b6170f1f0133e273cb85ede0e732048f.zip",
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strip_prefix = "rules_cc-1acf5213b6170f1f0133e273cb85ede0e732048f",
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integrity = "sha256-NddP6xi6LzsIHT8bMSVJ2NtoURbN+l3xpjvmIgB6aSg=",
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)
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http_archive = use_repo_rule("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
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http_archive(
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name = "arm_gcc_linux-x86_64",
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url = "https://developer.arm.com/-/media/Files/downloads/gnu/13.2.rel1/binrel/arm-gnu-toolchain-13.2.rel1-x86_64-arm-none-eabi.tar.xz",
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strip_prefix = "arm-gnu-toolchain-13.2.Rel1-x86_64-arm-none-eabi",
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build_file = "//bazel/toolchain:gcc_arm_none_eabi.BUILD",
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sha256 = "6cd1bbc1d9ae57312bcd169ae283153a9572bd6a8e4eeae2fedfbc33b115fdbb",
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)
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http_archive(
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name = "arm_gcc_win-x86_64",
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url = "https://developer.arm.com/-/media/Files/downloads/gnu/13.2.rel1/binrel/arm-gnu-toolchain-13.2.rel1-mingw-w64-i686-arm-none-eabi.zip",
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strip_prefix = "arm-gnu-toolchain-13.2.Rel1-mingw-w64-i686-arm-none-eabi",
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build_file = "//bazel/toolchain:gcc_arm_none_eabi.BUILD",
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sha256 = "51d933f00578aa28016c5e3c84f94403274ea7915539f8e56c13e2196437d18f",
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)
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http_archive(
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name = "arm_gcc_mac-x86_64",
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url = "https://developer.arm.com/-/media/Files/downloads/gnu/13.2.rel1/binrel/arm-gnu-toolchain-13.2.rel1-darwin-x86_64-arm-none-eabi.tar.xz",
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strip_prefix = "arm-gnu-toolchain-13.2.Rel1-darwin-x86_64-arm-none-eabi",
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build_file = "//bazel/toolchain:gcc_arm_none_eabi.BUILD",
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sha256 = "075faa4f3e8eb45e59144858202351a28706f54a6ec17eedd88c9fb9412372cc",
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)
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http_archive(
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name = "arm_gcc_mac-aarch64",
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url = "https://developer.arm.com/-/media/Files/downloads/gnu/13.2.rel1/binrel/arm-gnu-toolchain-13.2.rel1-darwin-arm64-arm-none-eabi.tar.xz",
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strip_prefix = "arm-gnu-toolchain-13.2.Rel1-darwin-arm64-arm-none-eabi",
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build_file = "//bazel/toolchain:gcc_arm_none_eabi.BUILD",
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sha256 = "39c44f8af42695b7b871df42e346c09fee670ea8dfc11f17083e296ea2b0d279",
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)
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# TODO: Provide tinyusb as a proper Bazel module.
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http_archive(
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name = "tinyusb",
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url = "https://github.com/hathach/tinyusb/archive/86c416d4c0fb38432460b3e11b08b9de76941bf5.zip",
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strip_prefix = "tinyusb-86c416d4c0fb38432460b3e11b08b9de76941bf5",
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build_file = "//src/rp2_common/tinyusb:tinyusb.BUILD",
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sha256 = "ac57109bba00d26ffa33312d5f334990ec9a9a4d82bf890ed8b825b4610d1da2",
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)
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register_toolchains(
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"//bazel/toolchain:arm_gcc_linux-x86_64",
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"//bazel/toolchain:arm_gcc_win-x86_64",
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"//bazel/toolchain:arm_gcc_mac-x86_64",
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"//bazel/toolchain:arm_gcc_mac-aarch64",
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)

‎bazel/BUILD.bazel

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package(default_visibility = ["//visibility:public"])
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py_binary(
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name = "generate_version_header",
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srcs = ["generate_version_header.py"],
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visibility = ["//:__subpackages__"],
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)
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# This isn't actually generated, it just uses the same name
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# to make it show up easier in searches.
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#
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# Rather than generating lists of headers to match CMake, the Bazel build
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# opts to have a static header that transitively include two known headers.
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# By default, empty header files are included, and users/platforms are expected
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# to specify an appropriate `cc_library` to replace them.
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#
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# You tell bazel which `cc_library` provides the respective headers by
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# configuring these `label_flag`s:
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#
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# # Specify the library that provides "pico_config_extra_headers.h"
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# --@pico-sdk//bazel/config:pico_config_extra_headers=//my_proj:my_custom_headers
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#
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# # Specify the library that provides "pico_config_platform_headers.h"
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# --@pico-sdk//bazel/config:pico_config_platform_headers=//my_proj:my_custom_platform_headers
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cc_library(
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name = "generate_config_header",
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hdrs = ["include/pico/config_autogen.h"],
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includes = ["include"],
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visibility = ["//:__subpackages__"],
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deps = [
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"//bazel/config:pico_config_extra_headers",
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"//bazel/config:pico_config_platform_headers",
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],
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)

‎bazel/README.md

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# Bazel build
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The Bazel build for the Pico SDK is currently community-maintained, and should
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be considered an experimental work-in-progress. There are missing features,
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and you may encounter significant breakages with future versions.
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You are welcome and encouraged to file issues for any problems you encounter
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along the way.
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## Using the Pico SDK in a Bazel project.
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### Add pico-sdk as a dependency
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First, in your `MODULE.bazel` file, add a dependency on the Pico SDK:
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```python
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bazel_dep(
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name = "pico-sdk",
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version = "1.6.0-rc1",
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)
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```
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Second, in the same file you'll need to add an explicit dependency on
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`rules_cc`, as it's a special-cased Bazel module:
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```python
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# Note: rules_cc is special-cased repository; a dependency on rules_cc in a
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# module will not ensure that the root Bazel module has that same version of
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# rules_cc. For that reason, this primarily acts as a FYI. You'll still need
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# to explicitly list this dependency in your own project's MODULE.bazel file.
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bazel_dep(name = "rules_cc", version = "0.0.10")
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# rules_cc v0.0.10 is not yet cut, so manually pull in the desired version.
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# This does not apply to dependent projects, so it needs to be copied to your
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# project's MODULE.bazel too.
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archive_override(
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module_name = "rules_cc",
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urls = "https://github.com/bazelbuild/rules_cc/archive/1acf5213b6170f1f0133e273cb85ede0e732048f.zip",
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strip_prefix = "rules_cc-1acf5213b6170f1f0133e273cb85ede0e732048f",
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integrity = "sha256-NddP6xi6LzsIHT8bMSVJ2NtoURbN+l3xpjvmIgB6aSg=",
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)
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```
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### Register toolchains
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These toolchains tell Bazel how to compile for ARM cores. Add the following
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to the `MODULE.bazel` for your project:
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```python
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register_toolchains(
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"@pico-sdk//bazel/toolchain:arm_gcc_linux-x86_64",
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"@pico-sdk//bazel/toolchain:arm_gcc_win-x86_64",
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"@pico-sdk//bazel/toolchain:arm_gcc_mac-x86_64",
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"@pico-sdk//bazel/toolchain:arm_gcc_mac-aarch64",
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)
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```
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### Enable required .bazelrc flags
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To use the toolchains provided by the Pico SDK, you'll need to enable a few
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new features. In your project's `.bazelrc`, add the following
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```
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# Required for new toolchain resolution API.
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build --incompatible_enable_cc_toolchain_resolution
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build --@rules_cc//cc/toolchains:experimental_enable_rule_based_toolchains
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```
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### Ready to build!
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You're now ready to start building Pico Projects in Bazel! When building,
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don't forget to specify `--platforms` so Bazel knows you're targeting the
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Raspberry Pi Pico:
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```console
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$ bazelisk build --platforms=@pico-sdk//bazel/platform:rp2040 //...
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```
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## SDK configuration [experimental]
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These configuration options are a work in progress and may see significant
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breaking changes in future versions.
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### Selecting a different board
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Currently there are three configurable flags for targeting a different board:
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1. `pico_config_extra_headers`: This should always point to a `cc_library `that
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provides a `"pico_config_extra_headers.h"` header. You can configure this
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by including a flag like the following in your build invocation:
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```
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--@pico-sdk//bazel/config:pico_config_extra_headers=//path/to:custom_extra_headers
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```
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2. `pico_config_platform_headers`: This should always point to a `cc_library`
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that provides a `"pico_config_platform_headers.h"` header.
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```
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--@pico-sdk//bazel/config:pico_config_platform_headers=//path/to:custom_platform_headers
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```
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3. `pico_config_header`: This should point to a `cc_library` that sets all
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necessary SDK defines. Most notably, `PICO_BOARD`, `PICO_CONFIG_HEADER`,
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`PICO_ON_DEVICE`, `PICO_NO_HARDWARE`, and `PICO_BUILD`. See
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`//src/boards:BUILD.bazel` for working examples. Any `defines` set on this
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library will propagate to the rest of the Pico SDK. To set this configuration
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option, pass a flag like the following in your Bazel build invocation:
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```
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--@pico-sdk//bazel/config:pico_config_platform_headers=//path/to:pico_board_config
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```
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### Selecting a stdio mode
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To select a different stdio mode, add it to your `platform` definition. For
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example:
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```python
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platform(
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name = "rp2040",
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constraint_values = [
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"@pico-sdk//bazel/constraint:rp2040",
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"@pico-sdk//bazel/constraint:stdio_usb", # Configures stdio_mode.
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"@platforms//cpu:armv6-m",
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],
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)
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```
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## Building the Pico SDK itself
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### First time setup
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You'll need Bazel (v7.0.0 or higher) or Bazelisk (a self-updating Bazel
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launcher) to build the Pico SDK.
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We strongly recommend you set up
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[Bazelisk](https://bazel.build/install/bazelisk).
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### Building
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To build all of the Pico SDK, run the following command:
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```console
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$ bazelisk build --platforms=//bazel/platform:rp2040 //...
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```
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**Note:** Since the Bazel build does not yet have any `cc_binary` rules with a
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`main()` function, there won't be any binaries to flash on your board. For now,
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this only builds the SDK as a collection of libraries.
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## Known issues and limitations
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The Bazel build is currently experimental and incomplete. At this time, only the
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stock Pi Pico board is supported, and the only configuration options are
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changing the STDIO mode between UART and USB serial.
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Keep in mind the following limitations:
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* Pico-W is not yet supported.
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* Selecting an alternative board is not yet supported.
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* Nearly all preexisting CMake configuration options are not yet supported.
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* Targeting the host build of the Pico SDK is not yet supported.

‎bazel/config/BUILD.bazel

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package(default_visibility = ["//visibility:public"])
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# This should always point to a cc_library that provides
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# a "pico_config_extra_headers.h".
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label_flag(
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name = "pico_config_extra_headers",
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build_setting_default = ":no_extra_headers",
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)
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# This should always point to a cc_library that provides
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# a "pico_config_platform_headers.h".
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label_flag(
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name = "pico_config_platform_headers",
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build_setting_default = ":no_platform_headers",
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)
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# This should always point to a cc_library that defines PICO_CONFIG_HEADER and
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# any other defines that should be applied when building the SDK.
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label_flag(
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name = "pico_config_header",
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build_setting_default = "//src/boards:default",
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)
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genrule(
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name = "empty_extra_headers_file",
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outs = ["generated_include/pico_config_extra_headers.h"],
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cmd = "echo > $@",
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cmd_bat = "copy NUL $@",
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visibility = ["//visibility:private"],
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)
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genrule(
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name = "empty_platform_headers_file",
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outs = ["generated_include/pico_config_platform_headers.h"],
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cmd = "echo > $@",
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cmd_bat = "copy NUL $@",
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visibility = ["//visibility:private"],
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)
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cc_library(
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name = "no_extra_headers",
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hdrs = ["generated_include/pico_config_extra_headers.h"],
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includes = ["generated_include"],
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visibility = ["//visibility:private"],
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)
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cc_library(
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name = "no_platform_headers",
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hdrs = ["generated_include/pico_config_platform_headers.h"],
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includes = ["generated_include"],
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visibility = ["//visibility:private"],
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)

‎bazel/constraint/BUILD.bazel

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package(default_visibility = ["//visibility:public"])
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# This constraint represents the dimension that guides the Pico SDK build. This
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# constraint will only ever enumerate specific MCUs (and the host), and does NOT
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# cover the differences from board-to-board.
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constraint_setting(
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name = "sdk_target",
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default_constraint_value = "host",
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)
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# This constraint value is used to guide the host build.
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constraint_value(
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name = "host",
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constraint_setting = ":sdk_target",
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)
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# This constraint value is used to guide parts of the build that are specific
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# to the rp2040.
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constraint_value(
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name = "rp2040",
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constraint_setting = ":sdk_target",
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)
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# This constraint value is used to guide parts of the build that apply to all
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# rp2-class chips.
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config_setting(
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name = "rp2",
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constraint_values = [
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":rp2040",
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],
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)
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# This constraint setting guides Bazel's build file evaluation differences
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# across different stdio configurations (e.g. stdio_usb needs TinyUSB).
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constraint_setting(
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name = "stdio_mode",
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default_constraint_value = "stdio_uart",
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)
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# When this constraint value is active, stdio is built against a hardware UART.
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constraint_value(
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name = "stdio_uart",
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constraint_setting = ":stdio_mode",
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)
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# When this constraint value is active, stdio is built against TinyUSB-based
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# USB serial.
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constraint_value(
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name = "stdio_usb",
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constraint_setting = ":stdio_mode",
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)
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# When this constraint value is active, stdio is built against an ARM
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# semihosting library.
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constraint_value(
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name = "stdio_semihosting",
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constraint_setting = ":stdio_mode",
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)

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