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rp2: Change order of pin operations to prevent glitches. #10337

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Merged
merged 1 commit into from
Jan 12, 2023
Merged

rp2: Change order of pin operations to prevent glitches. #10337

merged 1 commit into from
Jan 12, 2023

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pdg137
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@pdg137 pdg137 commented Dec 27, 2022 •
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Fixes #10226. When switching from a special function like SPI to an input or output, there was a brief period after the function was disabled but before the pin's I/O state was configured, in which the state would be poorly defined. This fixes the problem by switching off the special function after fully configuring the I/O state.

Test code:

from machine import SPI, Pin

sck = Pin(14)
mosi = Pin(15)

sck.init(mode=Pin.IN)
spi = SPI(id=1, baudrate=100000, polarity=0, phase=0, sck=sck, mosi=mosi)
spi.write(bytearray([0xAA]))
sck.init(mode=Pin.OUT, value=0)
sck(1)

Before/after this change (with 1k pull-up):

from machine import SPI, Pin

sck = Pin(14)
mosi = Pin(15)

sck.init(mode=Pin.OUT, value=1)
spi = SPI(id=1, baudrate=100000, polarity=0, phase=0, sck=sck, mosi=mosi)
spi.write(bytearray([0xAA]))

sck.init(mode=Pin.IN, pull=Pin.PULL_DOWN)
sck.init(mode=Pin.OUT, value=1)

Before/after this change (with no pull-up):

from machine import SPI, Pin

sck = Pin(14)
mosi = Pin(15)

sck.init(mode=Pin.OUT, value=0)
spi = SPI(id=1, baudrate=100000, polarity=1, phase=0, sck=sck, mosi=mosi)
spi.write(bytearray([0xAA]))

sck.init(mode=Pin.OPEN_DRAIN, value=0)

Before/after this change (with 10k pull-up):

As I noted in the issue, the last one seems weird since init apparently disobeys its value argument in open-drain mode.

@dpgeorge
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As I noted in the issue, the last one seems weird since init apparently disobeys its value argument in open-drain mode.

Yes that looks wrong. We can fix that in a separate PR.

@pdg137 @dpgeorge
rp2/mphalport: Change order of pin operations to prevent glitches.
b208cf2 
When switching from a special function like SPI to an input or output,
there was a brief period after the function was disabled but before the
pin's I/O state was configured, in which the state would be poorly defined.
This fixes the problem by switching off the special function after fully
configuring the I/O state.

Fixes micropython#10226.

Signed-off-by: Paul Grayson <[email protected]>
@dpgeorge dpgeorge merged commit b208cf2 into micropython:master Jan 12, 2023
@dpgeorge
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I rebased this on master and force pushed to your branch (so it checks CI, and so github can show it as merged), then merged.

tannewt added a commit to tannewt/circuitpython that referenced this pull request May 14, 2025
@tannewt
Merge pull request micropython#10337 from eightycc/pr-10325
0893345 
Updates to PR #10325
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RP2: 1us glitch on SCK pin when switching from SPI function to Pin.OUT
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@pdg137 @dpgeorge