On Mon, Jun 27, 2011 at 7:29 PM, Tom Schouten <t...@zwizwa.be> wrote: > On 06/27/2011 12:36 PM, Xiaofan Chen wrote: >>> Is there a known reason why this difference is so large? >>> ARM-USB-OCD hardware?
An High Speed FTDI2232H based device could be faster if you use this kind of non-intelligent adapter. Something with more intelligence (eg: MCU inside the J-Link Adapter) can help reduce the USB latency issue. >>> Adaptive clocking? (not on ARM-USB-OCD, but supported on SAM-ICE). I tend to think this is not the major issue. >>> Some other issue related to OpenOCD itself? >> >> I think all three are related with probably OpenOCD contribute the >> major portion. > > Any suggestion on where I might to look in the code to fix this? > What I find strange is that the data rate doesn't go proportional to the > clock speed. > > Maybe combination of communication delay and waiting for the ack when > sending out a page? Some other polling delay that's too large? > I do not know much about the internals of OpenOCD (not that interested to learn about Jtag, only interested in USB) but I think this thread should help: "USB latency limiting JTAG speed". I think Øyvind Harboe's suggestion is quite good. https://lists.berlios.de/pipermail/openocd-development/2010-October/016724.html https://lists.berlios.de/pipermail/openocd-development/2010-October/016727.html "One interesting modification to OpenOCD might be to add some profiling metrics on inter-jtag_execute_queue() times. If there are large inter-jtag_execute_queue() times then I'd expect an async interface to help." To use async interface, libusb-1.0 and libftdi can help (with quite significant code changes in the JTAG adapter driver side). But the higher level profiling about OpenOCD should come first. -- Xiaofan _______________________________________________ Openocd-development mailing list Openocd-development@lists.berlios.de https://lists.berlios.de/mailman/listinfo/openocd-development
