On Wednesday, August 25, 2010 02:43:59 Frans Meulenbroeks wrote: > 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.
i meant we should treat the frequency specified as the max allowed. if the host PC cant actually meet that timing, well nothing urjtag can do about it. but it certainly can keep from going too fast for a device to keep up. > 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. it isnt really in the realm of urjtag to try and figure out why communication isnt working. that is left to the monkey typing at the console. > 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. right, which is why we'd want to treat the frequency as a ceiling not to be exceeded. as for the "right" frequency for a particular board, that too is up to the user to determine. > 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). we have the "delay" mech already in place -- the frequency field of the cable. from that, we can easily calculate the min delay between pulses and leverage nanosleep() to fill the gaps if we go too fast. -mike
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