Visions for the Linux Kernel PWM Subsystem
summary
Proposes a new PWM framework that replaces sysfs with a char device API that supports atomic reconfiguration, a duty offset waveform abstraction, four kernel callbacks (query rounded result, query current hardware state, set rounded, set exact) and promises defined rounding behavior and a way to query what hardware will actually emit. Patches are at v5 on the pwm mailing list, prototypes on an STM32 dev board show about 400% speedup for reconfiguration versus sysfs; channel coupling remains future work.
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chapters (23)
- 0:00Introduction
- 1:52Motivation
- 3:19PWM basics
- 8:03Challenges
- 11:43Improvement ideas
- 12:06Channel coupling
- 13:53Duty offset
- 16:44ADC use case
- 17:05Exactness and rounding inconsistencies
- 17:47Querying hardware
- 18:29Picosecond debate
- 19:33Patches implemented
- 21:41New API details
- 26:31Q&A
- 28:13New vs CFS API
- 30:15Coupled PWM support
- 32:14Kernel timeline
- 33:05Arbitrary waveforms
- 34:35Coupling timeframe
- 36:10Multi-channel control
- 37:56Software coupling
- 39:10User space library
- 40:10Closing remarks
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