[I sent a similar this out just under 1 week ago, and have received
no replies ... so I'm sending this updated message in hopes that
someone will share their thoughts on how to proceed. - MLD]
I've tried all the USB / general coding speed tweaks that I can think
of and easily find / work out, all to no avail. I'm getting about 28
MBytes/s on my Mac at home (Dual G4 @ 1.25 GHz, 1.75 GB DRAM @ 167
MHz, cheapo PCI USB 2.0 card); and 17-19 MBps on our lab Mac (Dual G5
@ 2 GHz, 1 GB DRAM @ 1 GHz, with built-in USB 2.0).
I believe that the primary MacOS throughput issue is an added Apple-
provided application-layer library/API called "CoreFoundation" which
provides "ease of use" to the application writer. The next layer of
USB I/O transport is Darwin's "ports", which are part of the mach
kernel but can be somewhat accessed by the application layer. Going
to the "ports" directly would definitely speed throughput up, but
Apple's documentation doesn't give enough info on how to write the
programs, and I can find no examples of such programming. Most of
what I can find is via Apple's Darwin Source Code repository < http://
darwinsource.opendarwin.org/ >, reading through the source code to
figure out how to do things. I really shouldn't have to go to this
level to "just" get async USB to work!
If I can't use "ports" directly, then I can do that via a kernel
extension (KEXT), or "device driver" in older terms. The primary
issue blocking me investigating this option is that GR's use of
LIBUSB would need to be changed so that all USB calls go through the
FUSB code (which in turn could call LIBUSB or not as needed).
Various initialization routines (e.g. usb_init(), usb_find_busses
() ) would be moved to the KEXT, requiring new code in FUSB to access
those KEXT routines. Right now those routines are "hard coded" to
use LIBUSB (most are in usrp/host/lib/usrp_prims.cc ).
Thus, IMHO what needs to happen is to route -all- USB calls through
FUSB, so that there is 1 place to deal with "everything USB".
Thoughts? - MLD
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