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Do not use external pullups on CoreBoard F401RC
This board also has internal pullups, so the external one is not actually needed (and will even violate the USB spec when both are used together). This commit disabled the external pullups, but leaves the defines in comments, as future documentation. See also #1029.
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variants/Generic_F401Rx/variant.h

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@@ -127,8 +127,11 @@ extern "C" {
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#ifdef ARDUINO_CoreBoard_F401RC
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// USB, pull this pin low to enable the USB attach pullup
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#define USBD_ATTACH_PIN PD2
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#define USBD_ATTACH_LEVEL LOW
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// It is documented here, but not actually used, since there are also
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// internal pullups which are automatically used and using both would
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// violate the USB specification for pullup strength.
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//#define USBD_ATTACH_PIN PD2
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//#define USBD_ATTACH_LEVEL LOW
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#endif
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#ifdef __cplusplus

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