TimeDomain Data has No record header.

11jun08

Normal spectral data has an 8 byte record header with each dump of the spectrometer. Time domain data does not contain these 8 bytes. All of the bytes output with timedomain sampling are sampled data.T

Data and processing.

Data was taken on 11jun08 in timedomain mode. The setup was:

172.032 MHz clock
Decimate by 172 giving bandwidth of 1MHz.

16 bit sampling polA and polB in lower band. This gave 8 bytes/sample (2(16bits)*2(IQ)*2(polAB).

inject sine wave at .1 MHz from Center of band. This should give about 10 samples per period of the sine wave.
Data block was 0x100008 bytes long (2^20 bytes of data + 8 bytes of supposed rechdr).

In 1 data block there would be 2^20/8 = 131072 samples (if we ignore the 8 byte rec header).

Idl was used to read in and plot the data.

The idl routines assumed the 8 byte recheader.
4 records were written with 131072 samples each. The 8 bytes at the end of each block were skipped.

The plots show the sine wave as it crossed the record boundaries (.ps) (.pdf):

Each plot shows the last 20 samples of RecN and the first 20 samples of RecN+1
Each page has 4 plots for record 1,2,3,4
Page 1-4 shows polA real, polAImg, polA real,polB img.
the * are the data samples
The dashed red line is the boundary between record N and record N+1. It is placed 1/2 way between the two samples.

Conclusions:

Each boundary shows a missing data sample.
Idl skipped the last 8 bytes of each block thinking it was the record header. This is the missing data sample.
psrv.c, part of the online data taking program was byteswapping the last 8 bytes of each block (depending on the recorded datatype (8, 4 bits no swapping, 16 bits was swapped). So the the 8 bytes can not just be read in and used...
15jun08.. The data taking program psrv.c was updated to not mess with the last 8 bytes of a blk when i timedomain.. idl will also be updated.
Looking at the fpga code

TimeDomain: pdev/gx/sp/src/sp.v

line 592.. it always loads data into pack_lpf_dat
line 886.. pack_dat always gets pack_lpf_dat .. which is then sent out.

Spectral data.:pdev/gx/sp/src/sp.v

line 838: calls pack in pack.v to pack the data into pack_data
pack.v line 647. pack_data gets pack_status or the packed data depending on acc_frame.

So spectral data get the spectra + the 8 byte status
Time domain data only gets the data..

processing: x101/080611/chktmd.pro

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