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Rollup optional pull specification into getDigitalValue #156

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cefn opened this issue Jun 3, 2016 · 3 comments
Open

Rollup optional pull specification into getDigitalValue #156

cefn opened this issue Jun 3, 2016 · 3 comments
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@cefn
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cefn commented Jun 3, 2016 •
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This is a change request following some consensus on medium-term workarounds for the surprising pull-down defaults of digitalWrite (surprising for experienced makers anyway, although that doesn't mean wrong).

This originates in the downstream discussion at... bbcmicrobit/micropython#288 and also relates to the discussion of pull defaults

The request is to provide a signature for getDigitalValue which promotes visibility of software-controllable pull behaviour and makes the existing default pull-setting visible and more accessible, as well as seamlessly allowing getDigitalValue calls to be opinionated about pull, and encouraging the downstream languages to extend their own mappings of the getDigitalValue call to include pull specification.

THE PROPOSAL

Pull should be set by...

  • calling getDigitalValue with an explicit pull argument (this is the extra requested signature, of which the below is a special case of resorting to a default value for this argument)
  • calling getDigitalValue with no explicit pull at which point they are implicitly set to e.g. MICROBIT_PULL_DEFAULT which is currently pull-down, though there should is a separate discussion about this. If previously set, getDigitalValue without an explicit pull will not overwrite the value.
  • explicitly pulling a pin (but not as part of a getDigitalValue call).

An alternative to avoid the potential for getDigitalValue() to be mistakenly substituted for setDigitalValue() which would end up with the same argument signature and a single character difference, is to provide getPulledValue() but this does not have the benefit of encouraging downstream languages to track an existing API they are bound to, and they may remain oblivious to the need to expose this key operation.
@finneyj
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finneyj commented Jun 3, 2016 •
edited

Thanks @cefn. Agree with all that, except the last point. getDigitalValue() is the known name - I think we should stick with it.

I'll draft up a pull request (pun intended!) for review.

@cefn cefn mentioned this issue Jun 3, 2016
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finneyj added a commit that referenced this issue Jun 3, 2016
@finneyj
microbit: Added getDigitalValue overload for PullMode #156
4cf4803 
 - Introduced an overload to MicroBitIOPin::getDigitalValue() to permit the
setting of a specific pull mode at the time of reading.

 - Bugfix of MicroBitIOPin::setPull() to persist preferred pull settings

 - Added configuration options to allow the default PullMode to be set via
   compile time option through MicroBitConfig.h or YOTTA_CONFIG
@finneyj
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finneyj commented Jun 3, 2016

#158

@finneyj
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finneyj commented Jun 3, 2016

@cefn @dpgeorge @pelikhan

FYI, as requested. #158

finneyj added a commit that referenced this issue Jun 3, 2016
@finneyj
Merge pull request #158 from lancaster-university/156-readDigitalValu…
f214bc9 
…ePullOverload

microbit: Added getDigitalValue overload for PullMode #156
@finneyj finneyj mentioned this issue Sep 22, 2016
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@cefn @finneyj @alennie1993