Re: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
- Original Message - From: Thomas Schmid [EMAIL PROTECTED] To: Discuss gnuradio discuss-gnuradio@gnu.org Sent: Friday, June 16, 2006 4:49 AM Subject: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s? Hi, I was wondering why can the USRP only achieve 32 MByte/s, i.e. 256 Mbit/s whereas the USB 2.0 specifications are 480 MBit/s? The 32 Mbyte/s is mentioned in several earlier posts on the gnuradio mailing list archive and in the BBN report (freebsd section). One is 'full-speed' and the other is 'high-speed'. Different chips are required. Leon ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
Hi, I was wondering why can the USRP only achieve 32 MByte/s, i.e. 256 Mbit/s whereas the USB 2.0 specifications are 480 MBit/s? The 32 Mbyte/s is mentioned in several earlier posts on the gnuradio mailing list archive and in the BBN report (freebsd section). One is 'full-speed' and the other is 'high-speed'. Different chips are required. That is incorrect. Full speed is 12 megabits per second (1.5 megabytes/s) and the USRP doesn't do full speed, only high speed. The USRP easily does 256 megabits per second (32 megabytes/s). The USB 2.0 raw signalling rate is 480 megabits per second, or 60 megabytes per second. You can't get the full 480 because there is overhead from packet headers, time between packets, etc. We could probably squeeze a little more bandwidth out of the bus, but it isn't a priority for now. Matt ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
As a point of reference the SSRP was used in a radio astronomy application where maximum bandwidth was important and we were able to squeeze a little more than 40MB/s out of the bus. I think this says that there is a little more to be had but that the USRP is doing a pretty good job at 32MB/s... -David Carr Hi, I was wondering why can the USRP only achieve 32 MByte/s, i.e. 256 Mbit/s whereas the USB 2.0 specifications are 480 MBit/s? The 32 Mbyte/s is mentioned in several earlier posts on the gnuradio mailing list archive and in the BBN report (freebsd section). One is 'full-speed' and the other is 'high-speed'. Different chips are required. That is incorrect. Full speed is 12 megabits per second (1.5 megabytes/s) and the USRP doesn't do full speed, only high speed. The USRP easily does 256 megabits per second (32 megabytes/s). The USB 2.0 raw signalling rate is 480 megabits per second, or 60 megabytes per second. You can't get the full 480 because there is overhead from packet headers, time between packets, etc. We could probably squeeze a little more bandwidth out of the bus, but it isn't a priority for now. Matt ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
David Carr said: As a point of reference the SSRP was used in a radio astronomy application where maximum bandwidth was important and we were able to squeeze a little more than 40MB/s out of the bus. I think this says that there is a little more to be had but that the USRP is doing a pretty good job at 32MB/s... The SSRP and the USRP both use the same interface chip, but they run it in different modes. The SSRP doesn't support transmission, so it uses a fully-automated hardware mode. The USRP needs data to go both ways, so there are some firmware delays in the 8-bit processor that runs in the interface chip. If someone cared, it is probably possible to reprogram the firmware so that when no data is being transmitted, the automatic hardware mode is used. The firmware would have to know, or be told, when to switch in and out of this mode. But this would gain 25% more bandwidth! (A similar optimization could be done for transmit-only applications. It's mixed transmitting and receiving that takes more overhead. Also, few people have looked at that firmware code; it may be possible to optimize it further in other ways.) Making this change might also require changing the Verilog code in the FPGA, if the signals that it uses to communicate with the USB chip today aren't compatible with the fully automated hardware mode. If you're lucky, Matt and Eric already thought of that :-) while debugging the USB interface, which was a hairy process due to undocumented bugs in the USB chip. John PS: Hacking in similar places would also allow the USRP to run on USB 1.1 at 12 megabits/sec, for low sample rate applications. ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
Hi, I was wondering why can the USRP only achieve 32 MByte/s, i.e. 256 Mbit/s whereas the USB 2.0 specifications are 480 MBit/s? The 32 Mbyte/s is mentioned in several earlier posts on the gnuradio mailing list archive and in the BBN report (freebsd section). Thanks, Thomas ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
Re: [Discuss-gnuradio] USB2, 32 MByte/s or 480MBit/s?
On Friday 16 June 2006 13:19, Thomas Schmid wrote: I was wondering why can the USRP only achieve 32 MByte/s, i.e. 256 Mbit/s whereas the USB 2.0 specifications are 480 MBit/s? The 32 Mbyte/s is mentioned in several earlier posts on the gnuradio mailing list archive and in the BBN report (freebsd section). For starters USB only does 480MBit/sec on the physical layer. It has quite a number of overheads which prevent this throughput being fully realised. I believe the practical throughput IS higher that 256MBit/sec but I don't know for sure (or what the bottleneck is) -- Daniel O'Connor software and network engineer for Genesis Software - http://www.gsoft.com.au The nice thing about standards is that there are so many of them to choose from. -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C pgpoGWWixnrAI.pgp Description: PGP signature ___ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
