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

Sun Nov 20 13:20:58 EST 2016

Ian Stephenson (aka @sniffCode on twitter) had the SPI working with an
SDCard really reliably, back in May:

http://www.sniff.org.uk/2016/05/spi-explained-connecting-sd-cards-to.html

Might be worth comparing notes with him. Sniff uses the standard mbed SPI
driver, same as the micro:bit does.

Also double check your SPOL and SPHA settings to make sure they are
compatible with the receiving end.

https://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus#Clock_polarity_and_phase

David

___________________________________________________________
David Whale, B.Sc (Hons), MIET
*Software Engineer and IET Schools Liaison Officer, Essex*

On 20 November 2016 at 17:06, Nevil Hunt <nevil.hunt at hotmail.co.uk> wrote:

>  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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