Date: Sat, 10 May 2014 19:23:44 +0100 From: Mark R V Murray <markm@FreeBSD.org> To: Bakul Shah <bakul@bitblocks.com> Cc: freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: Fast cycle counter for ARM chips with SCC - patch for review. Message-ID: <1EFDD1B3-2B95-4B96-84B1-077E0CEB5BDC@FreeBSD.org> In-Reply-To: <7D5EE653-922D-4AF8-92A9-56344148FC7F@bitblocks.com> References: <22E12094-E6B2-42F9-94AB-014A702D17F2@FreeBSD.org> <7D5EE653-922D-4AF8-92A9-56344148FC7F@bitblocks.com>
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[-- Attachment #1 --] Hi I’m aware of this, thanks, but it is not relevant to the cyclecounter (except distantly). M On 10 May 2014, at 19:07, Bakul Shah <bakul@bitblocks.com> wrote: > FYI: BCM2835 has a built in h/w RNG (using a reverse biased transistor as an entropy source). Access to it was enabled in the RPi firmware around Jan 30, 2013. FWIW, it passes rngtest as well as FreeBSD's /dev/random (on x86/amd64) does. > For the spec. see http://pastehtml.com/view/crkxyohmp.rtxt > Referenced from this thread: http://www.raspberrypi.org/forums/viewtopic.php?f=29&t=19334&p=273944#p273944 > >> On May 10, 2014, at 10:39 AM, Mark R V Murray <markm@FreeBSD.org> wrote: >> >> Hi * >> >> This patch makes the ARM6 kernels that have an SCC coprocessor (RPI and WANDBOARD have them) get a MUCH better implementation of get_cyclecount(9), but not a perfect one. The incrementing rate is good (+- 1 per instruction), but its only 32 bits. Later, if there is interest, I may wish to fix that with an overflow interrupt, but for now its easily good enough for the kernel entropy harvesting service. Also, its MUUUCH more efficient; a simple read rather can calling the internal kernel binuptime(9) clock. >> >> Comments, please? I’m keen to commit. >> >> M >> -- >> Mark R V Murray >> <arm_ccnt_counter.diff> >> -- Mark R V Murray [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.22 (Darwin) Comment: GPGTools - http://gpgtools.org iQCVAwUBU25utt58vKOKE6LNAQrUWAQAobb8mbeS9SMpEJ1YvLU63jG2ObWRz54I dJclOCaKP5rtXI6YvOuGph3Fy5dIDw1S4D+RUVjuc62qWWqi1G/6shKlqlCYjFHb dDl/tLyX36HPjTMI2pS47XS7U0nELl+xdg7vOBbqT70DQb33kPtAXTJYcYlMcwJe pPrVTd6uVS8= =Tygf -----END PGP SIGNATURE-----help
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