On Friday 13 November 2009, Grant Likely wrote: > I'm concerned about the approach taken here. As I understand it, the > PWM signals are very similar to GPIOs in that each PWM device controls > an external signal line, just like GPIO lines.
PWM is not GPIO, and doesn't fit into a GPIO framework. Since *everything* boils down to one or more signal lines, your argument leads directly to Linux having no native hardware interface except GPIOs. Not ... practical. ;) > The difference being > that PWMs cannot do input, and has additional capabilities (can be > programmed with a signal; not just on/off/tristate) If you want to combine PWM with something else ... timers would be a better target. They're both fundamentally about periodic phenomena. And quite a lot of timers support PWM output modes... (A generic interface to hardware timers is lacking, too.) > What is the reason for bringing in an entirely new framework instead > of extending the GPIO API or gpiolib? I'm not too excited about > having two entirely different frameworks for what basically boils down > to "numbered signal pins". You seem to mis-understand what PWM is all about, then. The whole point of a PWM is to set up a periodic activity that will run without CPU intervention. GPIOs, on the other hand, are packaged for manual bit twiddling. While it's possible to create low-speed implementations of serial protocols using GPIOs (like 2-wire/I2C, one-wire, and various SPI variants), those are explicitly the high-overhead (and low performance) substitutes, to be used only when native hardware isn't available (or is broken etc). For example you won't often get 40 Mbit/sec SPI if you are bitbanging over GPIOs ... and if you do, it won't leave much CPU horsepower for much of anything else. - Dave -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
