esp-idf/components/README.md

Core Components

Overview

This document contains details about what the core components are, what they contain, and how they are organized.

Organization

The core components are organized into two groups.

The first group (referred to as G0 from now on) contains hal, xtensa and riscv (referred to as arch components from now on), esp_rom, esp_common, and soc. This group contain information about and low-level access to underlying hardware; or in the case of esp_common, hardware-agnostic code and utilities. These components can depend on each other, but as much as possible have no dependencies outside the group. The reason for this is that, due to the nature of what these components contain, the likelihood is high that a lot of other components will require these. Ideally, then, the dependency relationship only goes one way. This makes it easier for these components, as a group, to be usable in another project. One can conceivably implement a competing SDK to ESP-IDF on top of these components.

The second group (referred to as G1 from now on) sits at a higher level than the first group. This group contains the components esp_hw_support, esp_system, newlib, spi_flash, freertos, log, and heap. Like the first group, circular dependencies within the group are allowed; and being at a higher level, dependency on the first group is allowed. These components represent software mechanisms essential to building other components.

Descriptions

The following is a short description of the components mentioned above.

G0 Components

hal

Contains the hardware abstraction layer and low-level operation implementations for the various peripherals. The low-level functions assign meaningful names to register-level manipulations; the hardware abstraction provide operations one level above this, grouping these low-level functions into routines that achieve a meaningful action or state of the peripheral.

Example:

• spi_flash_ll_set_address is a low-level function part of the hardware abstraction spi_flash_hal_read_block

arch

Contains low-level architecture operations and definitions, including those for customizations (can be thought of on the same level as the low-level functions of hal). This can also contain files provided by the architecture vendor.

Example:

• xt_set_exception_handler
• rv_utils_intr_enable
• ERI_PERFMON_MAX

esp_common

Contains hardware-agnostic definitions, constants, macros, utilities, 'pure' and/or algorithmic functions that is useable by all other components (that is, barring there being a more appropriate component to put them in).

Example:

• BIT(nr) and other bit manipulation utilities in the future
• IDF_DEPRECATED(REASON)
• ESP_IDF_VERSION_MAJOR

soc

Contains description of the underlying hardware: register structure, addresses, pins, capabilities, etc.

Example:

• DR_REG_DPORT_BASE
• SOC_MCPWM_SUPPORTED
• uart_dev_s

esp_rom

Contains headers, linker scripts, abstraction layer, patches, and other related files to ROM functions.

Example:

• esp32.rom.eco3.ld
• rom/aes.h

G1 Components

spi_flash

SPI flash device access implementation.

freertos

FreeRTOS port to targets supported by ESP-IDF.

log

Logging library.

heap

Heap implementation.

newlib

Some functions n the standard library are implemented here, especially those needing other G1 components.

Example:

• malloc is implemented in terms of the component heap's functions
• gettimeofday is implemented in terms of system time in esp_system

esp_system

Contains implementation of system services and controls system behavior. The implementations here may take hardware resources and/or decide on a hardware state needed for support of a system service/feature/mechanism. Currently, this encompasses the following, but not limited to:

• Startup and initialization
• Panic and debug
• Reset and reset reason
• Task and interrupt watchdogs

esp_hw_support

Contains implementations that provide hardware operations, arbitration, or resource sharing, especially those that is used in the system. Unlike esp_system, implementations here do not decide on a hardware state or takes hardware resource, acting merely as facilitator to hardware access. Currently, this encompasses the following, but not limited to:

• Interrupt allocation
• Sleep functions
• Memory functions (external SPIRAM, async memory, etc.)
• Clock and clock control
• Random generation
• CPU utilities
• MAC settings

esp_hw_support vs esp_system

This section details list some implementations and the reason for placing it in either esp_hw_support or esp_system.

task_wdt.c (esp_system) vs intr_alloc.c (esp_hw_support)

The task watchdog fits the definition of taking and configuring hardware resources (wdt, interrupt) for implementation of a system service/mechanism.

This is in contrast with interrupt allocation that merely facilitates access to the underlying hardware for other implementations - drivers, user code, and even the task watchdog mentioned previously!

crosscore_int.c (esp_system)

The current implementation of crosscore interrupts is tightly coupled with a number of interrupt reasons associated with system services/mechanisms: REASON_YIELD (scheduler), REASON_FREQ_SWITCH (power management) REASON_PRINT_BACKTRACE (panic and debug).

However, if an implementation exists that makes it possible to register an arbitrary interrupt reason - a lower level inter-processor call if you will, then this implementation is a good candidate for esp_hw_support. The current implementation in esp_system can then just register the interrupt reasons mentioned above.

esp_mac.h, esp_chip_info.h, esp_random.h (esp_hw_support)

The functions in these headers used to be in esp_system.h, but have been split-off.

The remaining functions in esp_system.h are those that deal with system behavior, such as esp_register_shutdown_handler, or are proxy for other system components's APIs such as esp_get_free_heap_size.

The functions split-off from esp_system.h are much more hardware manipulation oriented such as: esp_read_mac, esp_random and esp_chip_info.