Dalam pengujian dan pengukuran, penyegerakan berbilang peranti bagi penyelarasan pemerolehan
data adalah sangat penting. Ini adalah kerana saluran yang terhad dalam satu peranti
dan perlunya saluran isyarat bercampur. Kini, pelbagai teknik penyegerakan berbilang peranti
telah dicadangkan seperti GPIB, VXI, PXI/PXIe, dan LXI. Tetapi, kosnya mahal dan memerlukan
ruang besar dan kabel atau perkakasan tambahan untuk pemasangan. Oleh itu, USB
2.0 dengan harga yang murah dan senang untuk dipasang telah dipertingkatkan untuk mempunyai
keupayaan penyegerakan. Terdapat beberapa kaedah penyegerakan dalam USB 2.0 seperti
"software-timed trigger", "external hardware trigger" dan "USB-inSync". "Software-timed
trigger" hanya diprogramkan dalam perisian dan mempunyai kelewatan di peringkat mikrosaat.
Selain itu, kelewatan bagi kedua-dua "external hardware trigger" dan "USB-inSync" adalah sehingga
peringkat nanosaat. Tetapi, mereka memerlukan perkakasan dan pemasangan tambahan
untuk menyegerakkan berbilang peranti. Bagi mengatasi kelemahan teknik-teknik semasa, satu
algoritma pemicuan berdasarkan teknologi USB 3.0 telah dicadangkan. Bungkusan Cap
Waktu Semasa dalam USB 3.0 telah digunakan dalam algoritma pemicuan ini. Tanpa apa-apa
tambahan perkakasan, algoritma pemicuan ini boleh memicu berbilang peranti USB 3.0 dalam
masa yang sama dengan kelewatannya sekitar 280 nanosaat. Di samping itu, algoritma pemicuan
ini mampu menyokong maksimum tiga hab USB 3.0 yang disambung berturut-turut dengan
tidak menjejaskan prestasinya. Secara ringkasnya, algoritma pemicuan ini telah menambah baik
kelewatan sebanyak 99.7% daripada "software-timed trigger" dan tanpa apa-apa tambahan
perkakasan ia lebih senang dipasang berbanding dengan "external hardware trigger".
_______________________________________________________________________________________________________
In test and measurement, synchronizing multiple devices to timely coordinate data acquisition
is crucial. This is due to the limited number of channels on a single device and the need
for mixed-signal channels. Currently, various techniques have been proposed for triggering
and synchronization among multiple devices such as GPIB, VXI, PXI/PXIe and LXI. However,
they are expensive and need large footprint and additional cable or hardware to set up.
Due to that, with the low cost and easy-to-setup USB 2.0, it is enhanced to have synchronization
ability. There are various synchronization methods in USB 2.0 such as software-timed
trigger, external hardware trigger and USB-inSync. The software-timed trigger is purely implemented
in software and has high trigger delay, which is up to microseconds. Besides that,
for both external hardware trigger and USB-inSync, they can achieve up to nanoseconds of synchronization
precision. However, both of those methods need extra hardware or setup to synchronize
multiple devices. In order to overcome these drawbacks from the existing techniques,
a trigger algorithm is proposed based on the study of USB 3.0 technology. The Isochronous
Timestamp Packet (ITP) in USB 3.0 is used as the main component in the trigger algorithm.
Without any hardware implementation, the trigger algorithm is able to trigger multiple USB
3.0 devices with a trigger delay around 280 ns. In addition, the trigger algorithm can support
up to maximum three consecutive connected hubs without affecting the performance. In short,
the trigger algorithm had improved the trigger delay from conventional software-timed trigger
by 99.7% and without any hardware implementation it is easier to set up compared to external
hardware trigger.
Triggering synchronization of multiple usb 3.0 devices using isochronous timestamp packet / Lim Chong Han