Oops. Did reply instead of reply all. Here is my response 2010/8/25 Frans Meulenbroeks <[email protected]>: > 2010/8/24 Mike Frysinger <[email protected]>: >> >> last i checked, there are two clocking functions ... one allows buffering and >> requires higher layers to flush the result, while the other is basically >> "toggle the line now". so someone might want to look into that if/when the >> kernel gets support. >> >> also, i noticed the gpio cable driver doesnt respect the active frequency. >> so >> at the moment, its frequency is basically "go as fast as possible" which >> could >> be too fast for some parts. we might have to revisit this at some point when >> someone complains, but in the mean time, i'll make a note in the source code >> about it. >> -mike > > Well the calibration loop is done (at least it tells me so). The > results seem to vary pretty wildly (I've seen values around 25k but > also 115k on my test setup). > But the value is used only to delay between changing CLK and reading TDO > > Probably the best way to measure the max frequency is by toggling a > gpio pin as fast as possible for a substantial time and determine the > frequency. > If the freq of the device is lower than this (so we're going too fast) > we could decide to emit a warning or error as the bare minimum. > Another source of dismay could be the io pins themselves. E.g. even > while thinking that you drive them at a 1-1 duty cycle it could be > that e.g. some capacitance in the system makes that this cycle is > deformed potentially making the pulses or gaps too small. > As a workaround gpio_set_value could contain a small macro which > evaluates to a while loop that introduces a fixed amound of delay > (controlled by a #define in the file). At least then someone can > easily add additional delay if the freq is too high. (especially > combined with the warning as mentioned before). > > Frans >
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