Difference between SPI Boot and Download Boot

Nhertec
Posts: 1
Joined: Wed Jun 20, 2018 12:00 am

Difference between SPI Boot and Download Boot

Postby Nhertec » Wed Jun 20, 2018 12:07 am

Hello guys,

I'm interresting about the configuration of strapping pins and i would like know what is the difference between SPI Boot and Download Boot?
I would like just program the ESP32 over JTAG port. Must I leave the configuration of strapping pins by default or there is something to do specific?

So sorry for this newbie's question but i'm a rookie on ESP32...

Thanks in advance ;)

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kolban
Posts: 1571
Joined: Mon Nov 16, 2015 4:43 pm
Location: Texas, USA

Re: Difference between SPI Boot and Download Boot

Postby kolban » Wed Jun 20, 2018 3:54 am

My understanding is that SPI boot is a "normal" boot meaning that the application logic found in SPI flash is loaded and branched to. With download boot, the ESP32 does not load the program in flash but instead runs a program found in ROM that starts reading the UART port. It expects to find command on that port transmitted by esptool. Commands include "Write the following to flash" which will then be followed by data which is written into the flash memory of the device. This is where the name "download" comes into play. We are effectively "downloading" a new application into flash memory. If the ESP32 is then rebooted in "SPI boot" mode, then the new program found in flash will be run.

As for JTAG ... I have nothing (sadly) to offer.
Free book on ESP32 available here: https://leanpub.com/kolban-ESP32
Available for ESP32 consulting.

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