8000 Trinket M0: SPI not working correctly · Issue #219 · adafruit/circuitpython · GitHub
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deshipu opened this issue Aug 31, 2017 · 7 comments · Fixed by #223
Closed

Trinket M0: SPI not working correctly #219

deshipu opened this issue Aug 31, 2017 · 7 comments · Fixed by #223

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@deshipu
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deshipu commented Aug 31, 2017

I'm trying to get a ST7735 display to work with Trinket M0, and it seems that Trinket's SPI behaves very strangely. Here is a screenshot of a capture of a fragment of the transmission:

cap1

and here is a close-up on one of the fragments:

cap2

Here's the complete capture for analysis:
cap.logicdata.zip

And here is the code that I used to capture that:

>>> import busio, digitalio, board
>>> from adafruit_rgb_display import st7735
>>> cs = digitalio.DigitalInOut(board.APA102_MOSI)
>>> dc = digitalio.DigitalInOut(board.D0)
>>> rst = digitalio.DigitalInOut(board.D1)
>>> spi = busio.SPI(clock=board.D3, MOSI=board.D4)
>>> d = st7735.ST7735R(spi, cs=cs, dc=dc, rst=rst)

Looking at the capture, two things are immediately striking:

  1. the polarity of the data line is wrong
  2. there are strange blips happening on both clock and data lines in between the actual bytes being transmitted
@tannewt
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tannewt commented Aug 31, 2017

Which channel is which?

@tannewt
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tannewt commented Aug 31, 2017

What version of CircuitPython are you using?

@deshipu
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deshipu commented Aug 31, 2017

Sorry, channel 0 is the clock, channel 1 is the data (channel 2 is the D/C). Running CircuitPython 1.0.0 that came flashed on the Teensy M0.

@deshipu
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deshipu commented Sep 1, 2017 •
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I figured out where the "blips" are coming from — the BusDevice library is calling spi.configure before every transmission, and that toggles the clock and data lines.

Commenting out that line from BusDevice makes the display work as expected.

@tannewt
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tannewt commented Sep 1, 2017

Weird! What settings do you have? Configure shouldn't do anything if the setting are the same as before. Relevant code is here: https://github.com/adafruit/circuitpython/blob/master/atmel-samd/common-hal/busio/SPI.c#L171

@deshipu
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deshipu commented Sep 1, 2017

I didn't touch the default settings — the code I pasted in this bug is the only thing running since reset. I agree it's weird, especially since it only happens on the Trinket M0 — the Feather M0 Express is fine.

@deshipu
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deshipu commented Sep 1, 2017

Actually, I don't see you setting the self->current_baudrate anywhere in that code?

@tannewt tannewt mentioned this issue Sep 1, 2017
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deshipu pushed a commit that referenced this issue Sep 1, 2017
@tannewt
atmel-samd: Remember SPI baudrate.
e2f39a8 
This prevents the SERCOM from blipping the data line on each
transaction and therefore fixes #219.
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atmel-samd: Remember SPI baudrate. tannewt/circuitpython
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