Startup serial noise?

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kwiley
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Joined: Wed May 16, 2018 5:53 pm
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Startup serial noise?

Post by kwiley » Thu Jun 13, 2019 3:19 pm

What is the noise that occurs at the beginning of a session, shown below? First there is some legitimate text showing various checksums, which I presume has to do with either initializing the chip itself, or with initializing the serial connection, but then following that there is what appears to be binary data -- or just pure noise. Is that literal electronic noise, as if the serial lines haven't even initialized proper voltages and DAC timings yet (which would be weird since it comes *after* the cleaner text pertaining to checksums), or is it "communication noise" of some sort, proper bytes being generated by the DAC, but some sort of nonASCII bytewise data that isn't meant to be interpreted by the textual serial REPL?

More precisely, how do I know when it is safe to start transmitting data? As you can see below, my script sends "ordinary reset" at startup. It also sends "woke from a deep sleep", as per the example in the deep sleep docs. Both occur immediately after the binary salad, which makes me think I need to either delay a period of time, or send a sequence of dummy bytes at startup, one or the other, to make sure things are ready to go.

Thoughts?

Code: Select all

>>> machine.reset()
>>> 
 ets Jan  8 2013,rst cause:2, boot mode:(3,6)

load 0x40100000, len 31020, room 16 
tail 12
chksum 0xd2
ho 0 tail 12 room 4
load 0x3ffe8000, len 1100, room 12 
tail 0
chksum 0x9a
load 0x3ffe8450, len 824, room 8 
tail 0
chksum 0xbd
csum 0xbd
����n��{��g|�ll$l`#��|;�$�o��n�d`��;�l�l�$`��r�l�d�l ��s�d���dl`rd��;$����#��c|l#��c|��Ądlb��'��o��$o���l��$d���$`�o����#l$䌎#���c$�#;dr$s�o����#c�p��b��䇜�$�$�c��g�߀�cc��8���#�����d�ordinary reset

MicroPython v1.10-8-g8b7039d7d on 2019-01-26; ESP module with ESP8266
Type "help()" for more information.
>>> 

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Roberthh
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Re: Startup serial noise?

Post by Roberthh » Thu Jun 13, 2019 3:42 pm

The serial noise is a boot message sent at 74880 baud. Something like " ets Jan 8 2013,rst cause:2, boot mode:(1,6)" and so on, much like the message you showed above.
As soon as MicroPython initializes, the baud rate is set to 115200.

kwiley
Posts: 67
Joined: Wed May 16, 2018 5:53 pm
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Re: Startup serial noise?

Post by kwiley » Fri Jun 14, 2019 2:34 am

Ok, that makes sense. Thanks.

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