Overview

This is not an officially supported Google product.

nlplatform provides driver implementations for multiple hardware platforms under a common interface. It is composed of several repositories, whose names start with platform/nlplatform*.

The central repository is platform/nlplatform; it is hardware-agnostic and defines interfaces implemented by the other, hardware-specific repositories. It also provides modules implemented in terms of those interfaces, and some compiler- and CPU-specific code. The nlgpio_button.[ch] module in platform/nlplatform is an example of a hardware agnostic module, built on top of the platform/nlgpio.h and platform/nlswtimer.h interfaces.

The hardware-specific repositories at the time of writing are:

• platform/nlplatform_sim
• platform/nlplatform_em358x
• platform/nlplatform_nrf52x
• platform/nlplatform_stm32l1
• platform/nlplatform_stm32l4

Products use nlplatform by building against both platform/nlplatform and one of the platform/nlplatform_<hw> implementations; it's always a pair.

Developers for a product that uses nlplatform access its functions and types by including nlplatform.h first, and then including specific platform interfaces afterward; the ordering is important and explained later.

#include <stdio.h>

#include <nlplatform.h>
#include <nlplatform/nlgpio.h>

int main(void)
{
    printf("Compelling example using platform GPIO below\n");

    //
    // Implementation left as an exercise for the reader.
    //

    return 0;
}

While platform/nlplatform defines all the interfaces in nlplatform, some types in those interfaces are defined by the hardware-specific implementation it's paired with, and others are provided by the product, through nlproduct_config.h.

For example, platform/nlplatform/include/nlgpio.h uses nlgpio_id_t, but doesn't define it; it's defined by the hardware-specific platform entries. In the em358x platform entry, it is defined by em3xx_gpio.h.

Similarly, platform/nlplatform/include/nltimer.h uses nltimer_id_t, but doesn't define it; it's defined by the product in its product_config.h.

The mechanism for embedding types from the product and hardware-specific platform entries in platform/nlplatform interfaces is carefully ordered, header-file inclusion. This is why clients of nlplatform must include nlplatform.h first.

Two lines near the top of nlplatform.h are crucial for this effort:

#include <nlplatform/nlreset_info.h> // Includes nlproduct_config.h
#include <nlplatform_soc.h>          // Provided by platform/nlplatform_<hw> implementation

For support with problems or to learn more please contact the Nest Embedded Platforms team at nest-embedded-os@google.com.

Available Build Features

Several preprocessor definitions are used to customize the platform/nlplatform* repositories.

The following build features are available in platform/nlplatform:

• BUILD_FEATURE_ANTENNA_DIVERSITY

  • Makes nlradio_set_prevent_antenna_switch() available in nlradio.h when defined.

• BUILD_FEATURE_BREADCRUMBS

  • Adds a LINKER_REPLACEABLE() function, crash_dump_breadcrumbs(), which stores fault information in breadcrumbs. This allows fault information to be recovered after a rebooting or power-cycling the device.

• BUILD_FEATURE_BUTTON_DEBOUNCE

  • Enables debouncing for nlgpio_button.c based buttons. The debounce interval is set by NL_BUTTON_DEBOUNCE_TIME_INTERVAL_MS.

• BUILD_FEATURE_FAT_FILES

  • Adds support for handling FAT files in nlfs.c.

• BUILD_FEATURE_FAULT_DUMP_TASK_STACKS

  • Dump backtraces for all tasks on fault when defined.

• BUILD_FEATURE_LOG_TOKENIZATION

  • Used to define UNIQUE_LOG_FORMAT_STRING() in nlplatform.h to support log tokenization. NOTE: This is currently unused.

• BUILD_FEATURE_NL_PLATFORM_SPI_IPC

  • Makes platform/nlspi_ipc.h, nlspi_ipc_work() and nspi_ipc_send() available.

• BUILD_FEATURE_NL_PROFILE

  • Makes platform/nlprofile.h available, which provides functions for task and resource profiling.

• BUILD_FEATURE_NL_TRACE

  • Makes platform/nltrace.h available, which provides functions for tracing events of interest available.

• BUILD_FEATURE_NO_BKPT_ON_FAULT

  • By default crash_dump_default(), in fault.c, executes a bkpt instruction (on ARM processors) to pause device execution when a debugger is connected. Defining BUILD_FEATURE_NO_BKPT_ON_FAULT disables this.

• BUILD_FEATURE_NO_SPI_FLASH

  • By default platform/nlflash_spi.h and platform/nlfs.h are available. Defining BUILD_FEATURE_NO_SPI_FLASH removes them.

• BUILD_FEATURE_PLATFORM_SPI_SLAVE_STATISTICS

  • By default platform/nlspi_slave.h is available. The functions in that interface related to SPI slave statistics are only included when this is defined.

• BUILD_FEATURE_PRE_WATCHDOG_ISR_EXTENSION

  • By default platform/nlwatchdog.h is available. Defining BUILD_FEATURE_PRE_WATCHDOG_ISR_EXTENSION makes nlwatchdog_ignore_pre_watchdog_isr() available (which must be implemented by a platform/nlplatform_<hw> entry). This function can effectively extend the HW watchdog timeout.

• BUILD_FEATURE_PRINTF_TOKENIZATION

  • Used in the cpu-specific implementations of fault.c and nlreset_info.c. When BUILD_FEATURE_PRINTF_TOKENIZATION is defined it allows for the tokeniztion of format strings in calls to printf(). When not defined, those format strings are made into unique string literals, allowing the linker to dead strip them when not used.

• BUILD_FEATURE_RAM_CONSOLE

  • The ram console stores the most recent log messages in a section of RAM; it's used for debugging. On fault, some things shouldn't be stored. When BUILD_FEATURE_RAM_CONSOLE is defined, the ram console is disabled in dump_context_default() in fault.c.

• BUILD_FEATURE_RESET_INFO

  • When defined, the device stores information about each reset it undergoes.

• BUILD_FEATURE_RESET_INFO_IN_TEMP_RAM

  • If defined BUILD_FEATURE_RESET_INFO must also be defined. Reset info must live in a section of RAM that persists across boots. This can be achieved either by dedicating a section of retained RAM to reset info, or using an overlaid section of retained RAM that the reset info owns between a reset and early in the next boot. Defining BUILD_FEATURE_RESET_INFO_IN_TEMP_RAM chooses the second option.

• BUILD_FEATURE_RESET_ON_FAULT

  • When defined the platform will call nlplatform_reset() on fault.

• BUILD_FEATURE_SOFT_PARTITIONS

  • When defined the partition table, stored in g_flash_partitions[], becomes writable.

• BUILD_FEATURE_SW_CRC

  • By default the platform/nlplatform_<hw> entry implements the functions defined in platform/nlcrc.h. When BUILD_FEATURE_SW_CRC is defined, a software based implementation, backed by platform/nlsystem/nlcrc, is used instead.

• BUILD_FEATURE_SW_TIMER

  • The software timer module uses an interrupt to provide a measure of time and provide several software timers to clients. Defining BUILD_FEATURE_SW_TIMER makes the module available through platform/nlswtimer.h.

• BUILD_FEATURE_SW_TIMER_USES_RTOS_TICK

  • If defined BUILD_FEATURE_SW_TIMER must also be defined. Defining this extends the platform/nlswtimer.h interface with functions for integrating the software timer module with an RTOS. This includes using the RTOS tick handler as the interrupt that drives the software timer module.

• BUILD_FEATURE_UNIT_TEST

  • When defined unit tests are built and some modules are instrumented with logic to permit unit testing.

TODO

Necessary for completeness:

• Add descriptions for NL_ -style configuration options in platform/nlplatform.