pw_system#
Warning
This module is an early work-in-progress towards an opinionated framework for new projects built on Pigweed. It is under active development, so stay tuned!
pw_system is quite different from typical Pigweed modules. Rather than providing a single slice of vertical functionality, pw_system pulls together many modules across Pigweed to construct a working system with RPC, Logging, an OS Abstraction layer, and more. pw_system exists to greatly simplify the process of starting a new project using Pigweed by drastically reducing the required configuration space required to go from first signs of on-device life to a more sophisticated production-ready system.
Trying out pw_system#
If you’d like to give pw_system a spin and have a STM32F429I Discovery board, refer to the board’s target documentation for instructions on how to build the demo and try things out
If you don’t have a discovery board, there’s a simulated device variation that you can run on your local machine with no additional hardware. Check out the steps for trying this out here.
Target Bringup#
Bringing up a new device is as easy as 1-2-3! (Kidding, this is a work in progress)
Create a ``pw_system_target`` in your GN build. This is what will control the configuration of your target from a build system level. This includes which compiler will be used, what architecture flags will be used, which backends will be used, and more. A large quantity of configuration will be pre-set to work with pw_system after you select the CPU and scheduler your target will use, but your target will likely need to set a few other things to get to a fully working state.
Write target-specific initialization. Most embedded devices require a linker script, manual initialization of memory, and some clock initialization. pw_system leaves this to users to implement as the exact initialization sequence can be very project-specific. All that’s required is that after early memory initialization and clock configuration is complete, your target initialization should call
pw::system::Init()
and then start the RTOS scheduler (e.g.vTaskStartScheduler()
).Implement ``pw::system::UserAppInit()`` in your application. This is where most of your project’s application-specific logic goes. This could be starting threads, registering RPC services, turning on Bluetooth, or more. In
UserAppInit()
, the RTOS will be running so you’re free to use OS primitives and use features that rely on threading (e.g. RPC, logging).
Pigweed’s stm32f429i_disc1_stm32cube
target demonstrates what’s required by
the first two steps. The third step is where you get to decide how to turn your
new platform into a project that does something cool! It might be as simple as
a blinking LED, or something more complex like a Bluetooth device that brews you
a cup of coffee whenever pw watch
kicks off a new build.
Note
Because of the nature of the hard-coded conditions in pw_system_target
,
you may find that some options are missing for various RTOSes and
architectures. The design of the GN integration is still a work-in-progress
to improve the scalability of this, but in the meantime the Pigweed team
welcomes contributions to expand the breadth of RTOSes and architectures
supported as pw_system_target
s.
GN Target Toolchain Template#
This module includes a target toolchain template called pw_system_target
that reduces the amount of work required to declare a target toolchain with
pre-selected backends for pw_log, pw_assert, pw_malloc, pw_thread, and more.
The configurability and extensibility of this template is relatively limited,
as this template serves as a “one-size-fits-all” starting point rather than
being foundational infrastructure.
# Declare a toolchain with suggested, compiler, compiler flags, and default
# backends.
pw_system_target("stm32f429i_disc1_stm32cube_size_optimized") {
# These options drive the logic for automatic configuration by this
# template.
cpu = PW_SYSTEM_CPU.CORTEX_M4F
scheduler = PW_SYSTEM_SCHEDULER.FREERTOS
# Optionally, override pw_system's defaults to build with clang.
system_toolchain = pw_toolchain_arm_clang
# The pre_init source set provides things like the interrupt vector table,
# pre-main init, and provision of FreeRTOS hooks.
link_deps = [ "$dir_pigweed/targets/stm32f429i_disc1_stm32cube:pre_init" ]
# These are hardware-specific options that set up this particular board.
# These are declared in ``declare_args()`` blocks throughout Pigweed. Any
# build arguments set by the user will be overridden by these settings.
build_args = {
pw_third_party_freertos_CONFIG = "$dir_pigweed/targets/stm32f429i_disc1_stm32cube:stm32f4xx_freertos_config"
pw_third_party_freertos_PORT = "$dir_pw_third_party/freertos:arm_cm4f"
pw_sys_io_BACKEND = dir_pw_sys_io_stm32cube
dir_pw_third_party_stm32cube = dir_pw_third_party_stm32cube_f4
pw_third_party_stm32cube_PRODUCT = "STM32F429xx"
pw_third_party_stm32cube_CONFIG =
"//targets/stm32f429i_disc1_stm32cube:stm32f4xx_hal_config"
pw_third_party_stm32cube_CORE_INIT = ""
pw_boot_cortex_m_LINK_CONFIG_DEFINES = [
"PW_BOOT_FLASH_BEGIN=0x08000200",
"PW_BOOT_FLASH_SIZE=2048K",
"PW_BOOT_HEAP_SIZE=7K",
"PW_BOOT_MIN_STACK_SIZE=1K",
"PW_BOOT_RAM_BEGIN=0x20000000",
"PW_BOOT_RAM_SIZE=192K",
"PW_BOOT_VECTOR_TABLE_BEGIN=0x08000000",
"PW_BOOT_VECTOR_TABLE_SIZE=512",
]
}
}
# Example for the Emcraft SmartFusion2 system-on-module
pw_system_target("emcraft_sf2_som_size_optimized") {
cpu = PW_SYSTEM_CPU.CORTEX_M3
scheduler = PW_SYSTEM_SCHEDULER.FREERTOS
link_deps = [ "$dir_pigweed/targets/emcraft_sf2_som:pre_init" ]
build_args = {
pw_log_BACKEND = dir_pw_log_basic #dir_pw_log_tokenized
pw_log_tokenized_HANDLER_BACKEND = "//pw_system:log"
pw_third_party_freertos_CONFIG = "$dir_pigweed/targets/emcraft_sf2_som:sf2_freertos_config"
pw_third_party_freertos_PORT = "$dir_pw_third_party/freertos:arm_cm3"
pw_sys_io_BACKEND = dir_pw_sys_io_emcraft_sf2
dir_pw_third_party_smartfusion_mss = dir_pw_third_party_smartfusion_mss_exported
pw_third_party_stm32cube_CONFIG =
"//targets/emcraft_sf2_som:sf2_mss_hal_config"
pw_third_party_stm32cube_CORE_INIT = ""
pw_boot_cortex_m_LINK_CONFIG_DEFINES = [
"PW_BOOT_FLASH_BEGIN=0x00000200",
"PW_BOOT_FLASH_SIZE=200K",
# TODO: b/235348465 - Currently "pw_tokenizer/detokenize_test" requires at
# least 6K bytes in heap when using pw_malloc_freelist. The heap size
# required for tests should be investigated.
"PW_BOOT_HEAP_SIZE=7K",
"PW_BOOT_MIN_STACK_SIZE=1K",
"PW_BOOT_RAM_BEGIN=0x20000000",
"PW_BOOT_RAM_SIZE=64K",
"PW_BOOT_VECTOR_TABLE_BEGIN=0x00000000",
"PW_BOOT_VECTOR_TABLE_SIZE=512",
]
}
}
Metrics#
The log backend is tracking metrics to illustrate how to use pw_metric and retrieve them using Device.get_and_log_metrics().
Console#
The pw-system-console
can be used to interact with the targets.
See pw_system CLI reference for detailed CLI usage information.
Multi-endpoint mode#
The default configuration serves all its traffic with the same
channel ID and RPC address. There is an alternative mode that assigns a separate
channel ID and address for logging. This can be useful if you want to separate logging and primary RPC to
pw_system
among multiple clients.
To use this mode, add the following to gn args out
:
pw_system_USE_MULTI_ENDPOINT_CONFIG = true
The settings for the channel ID and address can be found in the target
//pw_system:multi_endpoint_rpc_overrides
.
Extra logging channel#
In multi-processor devices, logs are typically forwarded to a primary
application-class core. By default, pw_system
assumes a simpler device
architecture where a single processor is communicating with an external host
system (e.g. a Linux workstation) for developer debugging. This means that
logging and RPCs are expected to coexist on the same channel. It is possible
to redirect the logs to a different RPC channel output by configuring
PW_SYSTEM_LOGGING_CHANNEL_ID
to a different channel ID, but this would
still mean that logs would inaccessible from either the application-class
processor, or the host system.
The logging multisink can be leveraged to address this completely by forwarding
a copy of the logs to the application-class core without impacting the behavior
of the debug communication channel. This allows pw-system-console
work as
usual, while also ensuring logs are available from the larger application-class
processor. Additionally, this allows the debug channel to easily be disabled in
production environments while maintaining the log forwarding path through the
larger processor.
An example configuration is provided below:
config("extra_logging_channel") {
defines = [ "PW_SYSTEM_EXTRA_LOGGING_CHANNEL_ID=2" ]
}
pw_system_target("my_system") {
global_configs = [ ":extra_logging_channel" ]
}
Once you have configured pw_system as shown in the example above, you will still need to define an RPC channel for the channel ID that you selected so the logs can be routed to the appropriate destination.