
ESP8266 superfast flashing: flash ESP in 5 seconds - rojer9
https://blog.cesanta.com/esp8266-superfast-flashing-flash-esp-in-5-seconds
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Already__Taken
There's something very satisfying about modern techniques walking into the old
way of doing things for orders of magnitude gains.

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pjc50
Yes, although this isn't quite that; this is a simple matter of turning the
serial link speed way, way up over the normal levels. It's probably dependent
on having a nice short cable, and since RS232 is single-ended rather than
differential there might be more EMI.

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cushychicken
Mmm, sort of doubt this. EMI would only be causing serious problems with a
return path - in this case the RX line, which wouldn't have much of an effect
on the transmitted byte stream since relatively little is coming back over the
UART_RX. Since this is all at 3.3V logic levels, I doubt there'd be much
crosstalk anyway.

If by "EMI" you mean some sort of signal quality issue due to transmission
line effects, I'd say that's probably closer to the truth, but still not
likely to be the case. At 1MBaud, your UART Tx will be switching in the range
of 12-15MHz. As long as your physical UART connection is under six inches or
so (and it probably would be if you were using a USB FTDI cable or something
like that), it'd be pretty hard to get seriously bad transmission line effects
at that frequency or most of the important harmonics in that square wave.

This sounds a little more like an additive error from a baud clock mismatch.
At some point, the FTDI is going to be generating a clock at some frequency
that isn't compatible with the ESP's receive oversampler. I'm inclined to
believe his explanation if he was able to show JTAG captures of the ESP's UART
error register.

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rojer9
at 1MBaud UART Tx will be switching at max of 512 KHz (if transmitting 0x55).

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cushychicken
The fact only enhances my point. You have to either be running a really high
speed signal or over a very long distance. I doubt either is happening in this
case.

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rojer9
yes, agreed.

