-----Original Message----- From: usb-bounces@opencores.org [mailto:usb-bounces@opencores.org]On Behalf Of i_rajesh1@rediffmail.com Sent: Wednesday, February 11, 2004 3:08 AM To: rudi@asics.ws; usb@opencores.org Subject: [usb] USB bw related calculations Hi Rudi, Thanks for the help regarding the Endpoints question. There was one more question. What does 1/2/3 in the UTMI 1/2/3 spec concern about.Can you help me out on what these numbers mean. And regarding the Bandwidth calculations i have come up with a summary(after referring a few docs).I have made it short and sweet.We are in the spec phase of the project and need to decide on HS/FS.Can you please have a look at it and point out any errors(if any :-)).This doc may also be of help to others who need to decide on many things during the spec phase. Thanks Rajesh +-------------+ BW calculations +-------------+ Choice of operation speed : (HS/FS/LS) Max BW in each case -------------------- One requirement is that transactions on the bus are always framed into 1ms quanta. This analysis model focuses on the number of byte transfers per frame (BTF) , e.g. it looks at the opportunities to transmit bytes in a 1ms time period even though the bus is a bit serial bus. ------------------------------------------------ Mode MaxBW BTF Utilizable %Util(max) ------------------------------------------------ HS 480 60000 1024*3*8 41 FS 12 1500 1023 68 ------------------------------------------------ Considering the HS case 480Mbps translates to 480M/(8*1000) = 60000 BTF. USB bandwidth is divided into 1,000 frames per second. Isochronous transfers in USB 1.1 were limited to a single packet per device endpoint per frame. The largest packet was 1,023 bytes, yielding an aggregate data transfer rate of 1Mbyte/sec. USB 2.0 not only increased the data rate to 480Mbits/sec., it also subdivided each of the frames into 8 microframes to reduce the need for buffering in the device. USB 2.0 also increased the number of 1,024 byte packets per microframe to 3 for each device. Thus, the achievable iso data rate in USB 2.0 jumps from 1Mbyte/sec. to 24Mbytes/sec. (1,000 frames/sec. x 8 microframes/frame x 3 packets/microframe x 1,024 bytes/packet). { Valid for HS only } ?? While streaming out video one important consideration will be whether the video out is compressed or not. => Considering the compressed data transfer case Normally Digital Video is compressed for transmission. Common standard is MPEG-2, designed for digital broadcast television level. Taking an example with the following requirement : 720x480 pixels per frame and 30 frames/sec,12 bits per pixel. BW = 720*480 pixels/frame * 30 frames/sec * 12 bits/pixel / {compression ratio } For a compression ratio=40 (max ?), required bandwidth is = 3.2 Mbits/s. (? Can be easily met by the FS port with lots of processing overhead) => Considering the raw data transfer case The chip receives the analog signal from the camera and converts it to a digital signal formatted to either CCIR-601 or CCIR-656. The CCIR-601 formatting requires an 8-bit data bus and three additional signals. One of those signals is the 27-MHz video input pixel clock. The two remaining signals provide the horizontal and vertical timing for the 8-bit data bus. The CCIR-656 format is similar to the CCIR-601 format. There is an 8-bit data bus with a 27-MHz clock. However, the vertical and horizontal timing codes are embedded within the data stream. Reqd BW = 27 Mbits per sec. (?FS cannot handle this) _______________________________________________ http://www.opencores.org/mailman/listinfo/usb