Jumps in hi res data 02oct14
02oct14 spectral channel jumps (top)
p2865 (Joanna) had trouble with a large number of
her scans on 02oct14. The scans had a large number of pfb overflows.
- 4 mock spectrometers covering:
- 4 bands of 86 MHz bandwidths centered at :
- 64 channels, 16 bits, 480 usec sampling.
- The clock was 172.032 MHz and the lowpass filter divider was
2 (giving the 86 MHz bw).
- the 1120-1220 MHz and 1320 hipass filters were used.
The fpgha bitflips in b1s1g0
- searching through the cima log file for the overflow messages
(skipping the first part where the setup was incorrect) there
- 2300 overflows b0s1g0 : 1170 band
- these looked like real rfi overflows
- 41202 overflows in b1s1g0 1420
- these were caused by bit flips in the fpga
- 0 overflows in b2s1g0 1520 band
- 401 overflows in b3s1g0 1620 band
- I looked at some of these overflows and they came from an
iridium satellite passing close to the beam
The plots show the fpga bit
flips in b1s1g0 from 1000 contiguous spectra figure over
plots (.ps) (.pdf)
- the data comes from the first row of file:
- 1000 spectra have been overplotted. each spectra is integrated
for 480 usecs.
- top frame: PolA spectra
- Bottom frame: PolB spectrra
- The jumps are bits flipping in the fpga.
- the constant amplitude is a higher order bit flipping from 0
- overflows were were seen in b0s1g0,b1s1g0,b3s1g0
- the b0s1g0 and b2s1g0 overflows came from rfi
- the b1s1g0 overflows came from fpga bitflips
- The bitflips in the fpga have been seen before (more
- This problem is intermittent.
- when a 172.032 MHz clock is used and the low pass filter is
used to narrow the bandwidth, these problems have occurred.
- Using the 172.032 MHz clock with no decimation does not
cause any problems.
- The error is probably in the low pass digital filter (only
used when decimating the full bandwidth).
diagnostics were run on 03oct14 to check for the bit
- the problem occurred (but not with b1s1g0).
- When the clock was 168MHz or less, the problem never
- Users who want
to decimate the full bandwidth of the mocks should use
clock frequencies of 168MHz or less
- this is a parameter in the mock setup.