Skip to content

Latest commit

 

History

History
52 lines (33 loc) · 1.45 KB

precache.rst

File metadata and controls

52 lines (33 loc) · 1.45 KB
Raw

IRAM pre-caching

Introduction

This is taken from the esp8266 arduino core. For details see:

See /information/flash for some background.

Code is always executed from IRAM, however it must be read in from flash memory on first use which can cause issues within timing-critical code.

This can be avoided by placing the code in IRAM. However, IRAM is a very limited resource and should generally be reserved for interrupt service routines.

An alternative solution is to arrange for critical code to be pre-loaded into IRAM before it starts execution.

Note

This cannot be used for interrupt service routines.

By their nature, interrupts are essentially random events and therefore code must be available in IRAM at any time.

Usage

The steps required are:

  1. Mark the function containing code using :cIRAM_PRECACHE_ATTR
  2. Place a call to :cIRAM_PRECACHE_START before the first line of critical code
  3. Place a call to :cIRAM_PRECACHE_END after the last line of critical code

You must always declare a tag to avoid the risk of section name conflicts.

You can find an example of how precaching is used here:

https://github.com/esp8266/Arduino/blob/master/cores/esp8266/core_esp8266_spi_utils.cpp

API Documentation

iram_precache