[Microbit-Python] SPI APIs on BBC micro:bit and ESP8266

[Nevil Hunt]

 Marc-Andre,


As regards...


* the connection is rather unreliable: we had lots of data loss or
  data corruption, with bytes not being transmitted or with lost bits
  - we tried several different baud rates without success


I'd certainly be interested if you can find out why.

I hooked a micro:bit up to a SPI RAM about a month ago and was able to write then read back from it, however it was a bit unreliable as sometimes the 'Reads' returned corrupted data.

>From my recollection it looked like it was the 'Write' that was getting corrupted as repeated 'Reads' always returned the same corrupted data.

I used the 'Bus Pirate' to try and debug it but I wasn't able to determine whether it was a h/w or s/w problem...then I ran out of time and haven't returned to it!

I have however been in touch with Paul from Microsoft who has a micro:bit talking to an SD Card with s/w written in 'C' so it looks like the micro:bit SPI interface can be made to work!


Cheers,


Nevil


________________________________
From: Microbit <microbit-bounces+nevil.hunt=hotmail.co.uk at python.org> on behalf of M.-A. Lemburg <mal at egenix.com>
Sent: 20 November 2016 15:04
To: For Pythonic MicroBit related discussions
Subject: [Microbit-Python] SPI APIs on BBC micro:bit and ESP8266

Hello,

over the weekend, we tried to get a connection from a BBC Microbit
to an ESP8266, both running the latest MicroPython for the resp.
platform, established via SPI.

We found several problems with this:

* the SPI APIs on the ESP8266 are all non-blocking and return
  whatever is currently in the buffer (using 0x00 for missing data
  and 0xff in case no connection is available)

* the SPI APIs on the Microbit are all blocking, only returning
  if all data is sent / received

* the connection is rather unreliable: we had lots of data loss or
  data corruption, with bytes not being transmitted or with lost bits
  - we tried several different baud rates without success

On the plus side, we did get SPI to work fine between two Microbits,
but that's not really what we were after, since we wanted to get
one of the Microbits in our mesh network connected to a WLAN and
work as gateway.

The blocking nature of the MB APIs make it difficult to write
interfaces which aim at being fault tolerant and work as
gateways. Having non-blocking versions would be better for this
sort of application.

Are there better ways to connect MBs and ESP8266 ?

We also tried I2C, but gave up, since the pins on the MB for
accessing I2C were too tiny to connect to without a breakout
board.

BTW: We were impressed by the new radio module. Getting MBs
to connect using these low level radios is really easy.

Cheers,
--
Marc-Andre Lemburg
eGenix.com

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