3.4 Planning for PCI Express

Transcription

1 3.4 Planning for PCI Express Evaluating Platforms for Performance and Reusability How many of you own a PC with PCIe slot? What about a PCI slot? 168

2 Advances in PC Bus Technology Do you remember this slide from the bus technology section earlier? We promised we would come back to it, so here we are to discuss the highlighted section PCI Express. As you can see, it has incredibly low latency and very high bandwidth. In fact, only PCI has lower latency, and nobody has higher bandwidth. This is an incredibly combination for test and measurement applications. 169

3 PCI Express Why do we care about PCI Express? It s FAST Serial interconnect at 2.5Gb/s PCI transactions are packetized and then serialized LVDS signaling, point-to-point, 8B/10B encoded x1 (by 1) gives real-world performance of 200 MB/s/direction x16 (by 16) gives real-world performance of 3.2 GB/s/direction Evolutionary version of PCI Uses same software model The main thing to take away about PCI Express is it s speed it is fast!!! How does it achieve the speed? It uses a serial interconnect at 2.5 gigabits per second. It takes the PCI transactions that previously existed and packetizes them and then serializes them using LVDS signaling in a point-to-point fashion with 8B/10B encoding. Note: LVDS stands for low-voltage differential signaling. Note: 8B/10B encoding is a correction method to balance digital transmissions. It has the effect of sapping 20% of the bitrate in the process, though. The by-one configuration (with one serial lane) gives performance of 200 megabytes per second per direction. (note the difference between bits and bytes on this slide). The by-sixteen configuration (with sixteen serial lanes) gives performance of 3.2 GB per second per direction. This is also a purely evolutionary version of PCI, meaning that all software support is 100% backward compatible. When NI released the PCI Express GPIB board last year, the driver development team didn t need to make ANY changes to the GPIB driver to support the new board. It looked exactly the same to the software as PCI. 170

4 PCI and PCIe Slots on a Motherboard Four PCI Slots Two x1 PCI Express Slots One x16 PCI Express Slot This picture represents how typical motherboards will look for years and probably decades to come. There will be PCI and PCI Express slots side-by-side in the way the PCI and ISA slots have been side-by-side for the last 10+ years. (You can still find ISA slots on motherboards today.) This also shows the size difference between the x1 slots and the x16 slots. The x16 slot in this picture replaces the AGP slot that previously existed for high-performance video applications. 171

5 ExpressCard : PCI Express for Laptops Laptops shipping January mm and 54 mm form-factors ExpressCard is the version of PCI Express that will replace PCMCIA or CardBus in laptop applications. Industry adoption is being driven by a $10 $15 cost reduction for Laptop manufacturers versus Cardbus. There are two main sizes represented here the ExpressCard 54 and ExpressCard 34. As you can see, the ExpressCard/34 can plug into 54 slot. As one example of performance, the ExpressCard 54 can have mini rotating hard-drives which is a lot of performance in a very small package. Laptops with ExpressCard slots first shipped January 2005 Technical note: both USB 2.0 and PCIe signaling is available on the host. Coming Modules IEEE-1394 Firewire A/B Bluetooth Flash Memory Gigabit Ethernet Wireless and many more to come 172

6 What is the PCI Express Bandwidth? Bus Bandwidth (MB/s) PCI (32-bit, 33 MHz) 132 (shared) x1 PCI Express 250 (per slot) x4 PCI Express 1000 (per slot) x16 PCI Express 4000 (per slot) Some report both directions versus single directions Example: x1 PCI Express 500 MB/s (Both Directions) 250 MB/s (Single Direction) 200 MB/s (Single Direction, packet overhead correction) Intel says x1 PCI Express is 500 Mbytes/s, but that is counting both directions. For Measurement Applications, 250 Mbytes/s is the number NI will be using. Then, with the overhead correction, the real-world number is right at 200 MB/s. But be aware of the different reporting in the industry. 250 MB/s * 8/10 (encoding) = 200 MB/s 173

7 Evolution of Industry Standard Buses Speed (Mbits/S) USB Ethernet PC Buses ISA 10 Mbit Ethernet PCI 32/ Mbit Ethernet USB 1.1 PCI Express Gigabit Ethernet USB X Year This is a picture of how industry-standard buses have evolved in the last 20 years. PC buses have maintained the highest performance over the years, but gigabit ethernet and USB 2.0 were catching up quickly. PCI Express raises the bar immensely, with over 40X the speed of gigabit Ethernet. Note: 40x is derived the following way: Gigabit Ethernet : 1000 MBit/s (1 Gbit/s) PCI Express x16 : 2.5 GBit/s times 16 lines = 40 Gbit/s 174

8 PCI Express Industry Adoption First PCI Express desktops shipped mid 2004 First ExpressCard laptops shipped January 2005 PCI and PCI Express are side-by-side in all Intel/Dell roadmaps Primary consumer drive is graphics processing (gamers, video editing) PCIe x16 slot replacing AGP As with any new bus, there will be a delayed adoption by the marketplace. PCI Express desktops began shipping mid-2004, and ExpressCard laptops started shipping in early All of the roadmaps from Intel and Dell currently have the PCI and PCIe slots side-by-side for many years to come this is a good thing for technology continuity and will help you preserve and continue your existing investment in PCI. Also, one of the initial drivers for PCI is the graphics processing capabilities from the higher bandwidth. 175

9 National Instruments PCI Express Roadmap PCIe Standard Complete First Desktops Shipping ExpressCard for Laptops PCIe GPIB PCIe CameraLink PXI-8196 w/ ExpressCard PCI and PCIe Products PXI 2.2 Compliant Products cpcie / PXIe Specification Work PXI and PXIe Products If you look specifically at NI s roadmap related to PCI Express, here is the timeline. 176

10 PCI Express Bandwidth Demonstration In applications that need high bandwidth, like high speed video acquisition, PCI Express enabled more data to be streamed to the PC, and thus a more accurate representation of the real-time event. Previously, applications like this either relied on less data to make a decision, or used very expensive, proprietary systems to meet their bandwidth needs. 177

11 Summary PCI and PCI Express will be offered side-by-side in Desktop PCs Mainstream acceptance of PCI indicates PCI availability for decades ISA still available today, remains popular in industrial segments PCI market size drove software compatibility for PCI Express PCI Express will enable new applications for Virtual Instrumentation Work to integrate PCI Express and PXI is underway Specifications in 2005, products in 2006 Compatibility will preserve investment, while increasing system performance 178