ESP8266 Community Forum

Community Answers.....

Here is an excellent question to ask the community for answers....

The flash chips connect to the ESP8266EX IC either via 2 data line or 4 data lines. 2 data lines is called DIO and 4 data lines is called QIO mode.

Why use QIO mode over DIO, or DIO over QIO?
Is there speed differences? and if yes are they notable? (or is the extra 2 I/O better used)
Why is there an option in Arduino IDE for 40Mhz and 80Mhz flash?
Why does the ESPTOOL.exe or ESPTOOL.py care if there it is DIO or QIO mode, is this not transparent?

Hoping to get community involvement to make clear this interface.

RichardS

PS. Maybe the best answer will be copied to the WIKI

Well choosing DIO should on the face of it reduce the speed both in flashing and at run time.
Practically it makes little difference since often performance is dictated by the speed of peripherals like sensors.
Now to free the pins that are captured by the default QIO the can needs to be removed and some pins lifted and another shorted to GND.
This is more or less a desperate measure and only taken if there is a definite shortage of pins and then only if you are one or two pins short.
The D9 D10 pins released must also be brought out on the PCB like they are on a 12E.
This means for more pins than two extra the solution lies with a port expander.

I've seen somewhere the speed differences, but I don't recall where.
DIO is not 50% of QIO, but If I remember, it is around 65%.
Uploader tools need to be aware of DIO or QIO mode not only to tell to the internal ROM bootloader how to access Flash for upload but also to tell this ROM bootloader to save flag saved somewhere how to boot next time it is power up. In other word, the ROM bootloader start booting, probably even in SIO, and when seeing that flag, it knows in which mode the Flash can be accessed, then shift into that mode.

I have noted on some modules that when you program through command line or Arduino IDE it works, but if you take the .bin file and use it with say ESP8266httpUpdate the module on next boot will fail and revert back to the original code... you get a:



I wonder if somehow this is related?

RichardS