<br><div>Hi Adam,</div><div><br></div><div>Thanks a lot! It is clear now.</div><div><br></div><div>Cheers,</div><div>Wu<br></div><br><blockquote name="replyContent" class="ReferenceQuote" style="padding-left:5px;margin-left:5px;border-left:#b6b6b6 2px solid;margin-right:0">-----原始邮件-----<br>
<b>发件人:</b><span id="rc_from">"Adam Deller" <adeller@gmail.com></span><br>
<b>发送时间:</b><span id="rc_senttime">2018-12-13 18:45:26 (星期四)</span><br>
<b>收件人:</b> "江悟" <jiangwu@shao.ac.cn><br>
<b>抄送:</b> difxusers <difx-users@listmgr.nrao.edu><br>
<b>主题:</b> Re: [Difx-users] VDIF data with sample granularity = 2<br><br><div dir="ltr">Hi Wu Jiang,<div><br></div><div>No, data will not be skipped. sample granularity is an internal concept for the mark 5 data stream, which tells it that it needs to treat the samples in blocks of "samplegranularity" wide together in order to unpack correctly. I misspoke earlier when I said the issue was integer number of nanoseconds, that is a different granularity (framegranularity, if you care :) ). samplegranularity effectively refers to how many different time samples are packed into the single unit of data that is unpacked at a time (typically 1 byte). If you have e.g. a datastream with 4x2 bit samples, then all the samples from a single time are packed together into 8 bits, and doing integer arithmetic on a byte pointer will always get you to the right place to start unpacking. But if you only have 2x2 bit samples in the stream, then that's only 4 bits altogether per time, and there are two different times that would point to the same byte (one wants the first nibble, one wants the second nibble). Hence the concept of sample granularity.</div><div><br></div><div>Cheers,</div><div>Adam</div></div><br><div class="gmail_quote"><div dir="ltr">On Thu, 13 Dec 2018 at 19:47, 江悟 <<a href="mailto:jiangwu@shao.ac.cn" target="_blank">jiangwu@shao.ac.cn</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br><div>Hi Adam and all,</div><div><br></div><div>As I discussed with Adam already, I still not sure if some part of the raw data would be skipped to load for correlation when sample granularity = 2. Any comments?</div><div><br></div><div>Cheers,</div><div>Wu<br></div><br><blockquote name="replyContent" class="m_-6335010022366877543ReferenceQuote" style="padding-left:5px;margin-left:5px;border-left:#b6b6b6 2px solid;margin-right:0">-----原始邮件-----<br>
<b>发件人:</b><span id="m_-6335010022366877543rc_from">"Adam Deller" <<a href="mailto:adeller@gmail.com" target="_blank">adeller@gmail.com</a>></span><br>
<b>发送时间:</b><span id="m_-6335010022366877543rc_senttime">2018-12-13 15:22:30 (星期四)</span><br>
<b>收件人:</b> "江悟" <<a href="mailto:jiangwu@shao.ac.cn" target="_blank">jiangwu@shao.ac.cn</a>><br>
<b>抄送:</b> <br>
<b>主题:</b> Re: VDIF data with sample granularity = 2<br><br><div dir="ltr">HI Wu Jiang,<div><br></div><div>Can you please send emails like this to the difx-users mailing list, rather than to me direct? sample granularity 2 means that the data reader will only see a timestamp with an integer number of nanoseconds every second time it unpacks a group of samples. This is because of the very high sampling rate.</div><div><br></div><div>Cheers,</div><div>Adam</div><div><br></div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Thu, 13 Dec 2018 at 11:43, 江悟 <<a href="mailto:jiangwu@shao.ac.cn" target="_blank">jiangwu@shao.ac.cn</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear Adam,<br><br>Recently when I made correlations with VDIF data streams, DiFX decoded the data format and gave some information as follows.<br>Mark5 stream: 0x2e2dc80<br> stream = File-1/1=/Bgfsdata/astro/raw/fa02/scan1.source.1045.vdif<br> format = VDIF_4096-6400-2-2 = 3<br> start mjd/sec = 58454 40673.694666240<br> frame duration = 5120.00 ns<br> framenum = 0<br> sample rate = 1600000000 Hz<br> offset = 0<br> framebytes = 4128 bytes<br> datasize = 4096 bytes<br> sample granularity = 2<br> frame granularity = 1<br> gframens = 5120<br> payload offset = 32<br> read position = 0<br> data window size = 1048576 bytes<br>Where, I am not quite sure about "the sample granularity = 2", as always I just see "sample granularity = 1" in many cases. Does it mean DiFX recognizes the samples in the data stream are not continuously allocated? Such as sample_ch1 sample_ch2 x x sample_ch1 sample_ch2 x x. However, actually the samples in the data stream are continuously recorded. So I would like to make clear on what DiFX deals with the data? <br>Thank you!<br><br>Best regards,<br>Wu Jiang<br></blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="m_-6335010022366877543gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8000001907349px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================================================!<br>Dr. Adam Deller </div><div dir="ltr" style="font-size:12.8px">ARC Future Fellow, Senior Lecturer</div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: +61 3 9214 5307</div><div style="font-size:12.8px">fax: +61 3 9214 8797</div><div style="font-size:12.8px"><br><span style="font-size:12.8px">office days (usually): Mon-Thu</span><br>!=============================================================!</div></div></div></div></div></div></div></div></div></div></div></div></div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr" style="font-size:12.8000001907349px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px"><div dir="ltr" style="font-size:12.8px">!=============================================================!<br>Dr. Adam Deller </div><div dir="ltr" style="font-size:12.8px">ARC Future Fellow, Senior Lecturer</div><div style="font-size:12.8px">Centre for Astrophysics & Supercomputing </div><div dir="ltr" style="font-size:12.8px">Swinburne University of Technology <br>John St, Hawthorn VIC 3122 Australia</div><div style="font-size:12.8px">phone: +61 3 9214 5307</div><div style="font-size:12.8px">fax: +61 3 9214 8797</div><div style="font-size:12.8px"><br><span style="font-size:12.8px">office days (usually): Mon-Thu</span><br>!=============================================================!</div></div></div></div></div></div></div></div></div></div></div></div></div>
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