On 8/24/2015 6:12 PM, Andrew P. Lentvorski wrote: > I've been trying to hunt down the maximum frequency on the BeagleBone Black > GPIO pins. > > This *seems* to be dominated by the transaction latency across the L3/L4 > interconnect. Fair enough. So ... > > What's the latency number? > > I've *measured* about 166ns per transaction (I can create a roughly 3MHz > toggle which is 2 pin flips which requires 6MTransactions/s which is > 166.66ns per transaction). But I don't know how to *calculate* that number > from the documentation.
I've measured 40 ns from the PRU. I'm not sure if the CPU can match this, but I'd be surprised if it couldn't. > I've been through the TI reference manuals, the TI support forums, and a > bunch of other things, but *nobody* seems to be able to cough up an actual > number for this. This is a bit lower level than you'll find in most reference manuals, and falls into the category of "if it's _really_ important to you, contact the manufacturer and verify"...and I hope you're buying a *LOT* of parts, because this is the sort of thing that is subject to change with die revisions. :) > Anybody have some references to frequencies and bus wait numbers? They may > be out there, but GTMF/RTFM doesn't seem to be sufficient. > > I don't need turbo speed, but the fact that it's entirely possible that I > may not even be able run at 1MHz (something *painfully* easy for most M0 or > M3/M4 cores) is, frankly, a bit of a shock. So from my measurements with the PRU, the sustained write speed for the GPIO is 40 ns per write. With the GPIO clock at 100 MHz, that's 2.5 clocks per write, which is actually a pretty respectable round-trip synchronization delay for crossing the various clock domains involved. -- Charles Steinkuehler [email protected] -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
