Minimum external clock for FPGA?

Hi all,
I’ve seen posts about folks providing an external clock of 44 MHz to the
USRP, and with a few software tweaks, getting it to work. I’m wondering
if
there is a floor as to how low this clock be reduced without causing
problems. I know some A/D converters have minimum sample rates, but the
AD9862 datasheet doesn’t seem to indicate that it does. Is there any
reason
I couldn’t run my USRP with an external reference at 26 MHz? How 'bout
10
MHz?

The only datapoint I could find was a reference to the fact that the
current
openBTS FPGA image doesn’t run (?) at 26 MHz due to a “firmware fix”
that is
needed, though I’m guessing that is referencing the FPGA code:

http://www.mail-archive.com/[email protected]/msg21130.html

I’ll probably make the USRP hardware modification on Monday to try these
out
with an external sig gen, but I figured I’d throw the question to the
list
prior to that to see if I could get a definitive answer.

Thanks much…

John -

It is my understanding that the current FPGA image used for OpenBTS
will fail on the transmit side if the FPGA clock is slower than the
USB clock. The USB clock is 48 MHz.

Also, the GSM symbol clock is derived from 13 MHz, so if you use a
multiple-of-13 clock, you can simplify a lot of the decimation.

These two facts together led us to choose 52 MHz for the current
OpenBTS USRP clock.

– David

On Jan 16, 2010, at 4:33 PM, John O. wrote:

the current openBTS FPGA image doesn’t run (?) at 26 MHz due to a
Thanks much…
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
David A. Burgess
Kestrel Signal Processing, Inc.

It is my understanding that the current FPGA image used for OpenBTS will
fail on the transmit side if the FPGA clock is slower than the USB clock.
The USB clock is 48 MHz.

If you (or anyone else involved) can provide the details of what the
issue
is here, I may have some time to dive in and potentially come up with a
fix. Let me know if interested.

Also, the GSM symbol clock is derived from 13 MHz, so if you use a
multiple-of-13 clock, you can simplify a lot of the decimation.

These two facts together led us to choose 52 MHz for the current OpenBTS
USRP clock.

Gotcha. Thanks for the quick response David.

Anyone else know of any other issues that would prevent the FPGA from
being
clocked at lower speeds?

Hi,
Please help.
during installation of ariprobe I got following errors:

out_pcap.c:8:18: error: pcap.h: No such file or directory
out_pcap.c: In function ‘write_pcap_file_header’:
out_pcap.c:34: error: storage size of ‘pfh’ isn’t known
out_pcap.c:37: error: ‘PCAP_VERSION_MAJOR’ undeclared (first use in this
function)
out_pcap.c:37: error: (Each undeclared identifier is reported only once
out_pcap.c:37: error: for each function it appears in.)
out_pcap.c:38: error: ‘PCAP_VERSION_MINOR’ undeclared (first use in this
function)
out_pcap.c: In function ‘write_pcap_packet’:
out_pcap.c:104: warning: incompatible implicit declaration of built-in
function ‘memcpy’
make[4]: *** [out_pcap.lo] Error 1
make[4]: Leaving directory /home/sandeep/airprobe/gsm-tvoid/src/lib' make[3]: *** [all] Error 2 make[3]: Leaving directory/home/sandeep/airprobe/gsm-tvoid/src/lib’
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory /home/sandeep/airprobe/gsm-tvoid/src' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory/home/sandeep/airprobe/gsm-tvoid’
make: *** [all] Error 2
[email protected]:~/airprobe/gsm-tvoid$

I am using ubantu 9.1(karmic), gnuradio-3.2.2 and airprobe is installed
via
git.
Kindly help me please

On 01/17/2010 07:01 PM, John O. wrote:

Also, the GSM symbol clock is derived from 13 MHz, so if you use a
multiple-of-13 clock, you can simplify a lot of the decimation.

These two facts together led us to choose 52 MHz for the current
OpenBTS USRP clock.

Gotcha. Thanks for the quick response David.

Anyone else know of any other issues that would prevent the FPGA from
being clocked at lower speeds?

The 9862 is only spec’ed down to 10 MHz.

Matt

Hi all,
while I am trying to install gsm-receiver in airprobe, during make I got
following errors:

Making all in openbtsstuff
make[6]: Entering directory
/home/sandeep/airprobe/gsm-receiver/debug/src/lib/decoder/openbtsstuff' /bin/bash ../../../../libtool --tag=CXX --mode=compile g++ -DHAVE_CONFIG_H -I. -I../../../../../src/lib/decoder/openbtsstuff -I../../../.. -I../../../../../src/lib/decoder -I../../../../../src/lib -I/usr/local/include/gnuradio -I../../../../../src/lib/decoder/openbtsstuff -g -O2 -Wall -Woverloaded-virtual -pthread -MT GSMCommon.lo -MD -MP -MF .deps/GSMCommon.Tpo -c -o GSMCommon.lo ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp libtool: compile: g++ -DHAVE_CONFIG_H -I. -I../../../../../src/lib/decoder/openbtsstuff -I../../../.. -I../../../../../src/lib/decoder -I../../../../../src/lib -I/usr/local/include/gnuradio -I../../../../../src/lib/decoder/openbtsstuff -g -O2 -Wall -Woverloaded-virtual -pthread -MT GSMCommon.lo -MD -MP -MF .deps/GSMCommon.Tpo -c ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp -fPIC -DPIC -o .libs/GSMCommon.o In file included from ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.h:34, from ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp:23: ../../../../../src/lib/decoder/openbtsstuff/Timeval.h:73: error: ‘uint32_t’ does not name a type ../../../../../src/lib/decoder/openbtsstuff/Timeval.h:74: error: ‘uint32_t’ does not name a type ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp: In member function ‘int32_t GSM::Clock::FN() const’: ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp:169: error: ‘class Timeval’ has no member named ‘sec’ ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp:169: error: ‘const class Timeval’ has no member named ‘sec’ ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp:170: error: ‘class Timeval’ has no member named ‘usec’ ../../../../../src/lib/decoder/openbtsstuff/GSMCommon.cpp:170: error: ‘const class Timeval’ has no member named ‘usec’ make[6]: *** [GSMCommon.lo] Error 1 make[6]: Leaving directory/home/sandeep/airprobe/gsm-receiver/debug/src/lib/decoder/openbtsstuff’
make[5]: *** [all-recursive] Error 1
make[5]: Leaving directory
/home/sandeep/airprobe/gsm-receiver/debug/src/lib/decoder' make[4]: *** [all-recursive] Error 1 make[4]: Leaving directory/home/sandeep/airprobe/gsm-receiver/debug/src/lib’
make[3]: *** [all] Error 2
make[3]: Leaving directory
/home/sandeep/airprobe/gsm-receiver/debug/src/lib' make[2]: *** [all-recursive] Error 1 make[2]: Leaving directory/home/sandeep/airprobe/gsm-receiver/debug/src’
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/home/sandeep/airprobe/gsm-receiver/debug’
make: *** [all] Error 2
[email protected]:~/airprobe/gsm-receiver/debug$

please help me to sort out the reason I am unable to find.

On Tue, Jan 19, 2010 at 01:56:39AM +0530, sandeep mishra wrote:

Hi all,
while I am trying to install gsm-receiver in airprobe, during make I got
following errors:

Wrong list.

Please post your question to airprobe-main.

Eric

On 01/18/2010 12:53 AM, sandeep mishra wrote:

out_pcap.c:37: error: for each function it appears in.)
make[2]: Leaving directory /home/sandeep/airprobe/gsm-tvoid/src' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory/home/sandeep/airprobe/gsm-tvoid’
make: *** [all] Error 2
[email protected]:~/airprobe/gsm-tvoid$

I am using ubantu 9.1(karmic), gnuradio-3.2.2 and airprobe is installed via
git.
Kindly help me please

What does this have to do with “Minimum external clock for FPGA”?

You are probably missing development files for pcap. Hence the
out_pcap.c:8:18: error: pcap.h: No such file or directory

try installing something like: libpcap0.8-dev - development library and
header files for libpcap0.8

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