Boot Process

Overview

• Reset vector is 0x40000080.
• Boots into Espressif code in IROM0.
• Loads SPI ROM data.
• Starts executing ESP SDK-code shadowed SPI ROM (unconfirmed).

ESP Boot Modes

The Espressif code can boot in different modes, selected on power-up based on GPIO pin levels.

MTDO	GPIO0	GPIO2	Mode	Description
L	L	H	UART	Download code from UART
L	H	H	Flash	Boot from SPI Flash
H	x	x	SDIO	Boot from SD-card

Processor Modes

• Only Ring 0 used
• TLBs (D and I) are set to
  • 0x00000000-0x1FFFFFFF: Illegal
  • 0x20000000-0x5FFFFFFF: RWX, Cache Write-Through
  • 0x60000000-0xFFFFFFFF: RWX, Bypass Cache

References

• Chinese seller with boot modes
• Translated boot modes
• ESP8266_Module Application Design Guide Chinese.pdf