High-speed buses and testing requirements on PC chipsets

1 X58



Intel's X58 chipset is the most advanced chipset on PC today, and is also the only chipset that supports Intel I7 CPU. In addition to integrating the most common high-speed serial bus, this chipset also has a major feature: it supports Intel's own QPI bus. The biggest difference between I7 and Intel's previous CPUs is that it integrates a memory controller like AMD K8 and supports 3-channel DDR3 memory. X58 supports 36-Lane PCIE G2, CroosFire, and can directly support SLI through NVIDIA's authorization. Let's take a look at the test requirements of these high-speed serial buses.


QPI



Intel's Quick Path Interface was first introduced on the I7 CPU, using peer-to-peer transmission similar to PCIE, replacing the previous parallel FSB. There are two bit rates for QPI: 4.8Gbps and 6.4Gbps. For 6.4Gbps QPI, when 32bit transmission is used, the bandwidth can reach 25.6GB/s. Compared to the 1600MHz FSB bandwidth of 12.8GB/s, the bandwidth has doubled. It is also better than AMD's HT 3.0 with a bit rate of 5.2Gbps and a bandwidth of 20.8GB/s when transmitting 32bit. At the same time, QPI can not only be used for the interconnection between the CPU and the north bridge chip, but also for the internal interconnection between multi-core processors and the interconnection with the memory controller.

Since the fundamental wave of QPI 6.4Gbps is 3.2GHz, the 1.8bit rate is 11.52GHz, and the 5th harmonic is 16GHz, an oscilloscope with a bandwidth of 16GHz is required for testing. Tektronix and LeCroy both have oscilloscopes with bandwidths above 16GHz, but LeCroy currently has no QPI test solution. Tektronix is ​​the first company in the industry to launch an oscilloscope-based QPI test solution, while Agilent has launched the bit error rate tester J-BERT N4903B.



PCI Express 2.0

PCIE G2 has a bit rate of 5Gbps, a fundamental frequency of 2.5GHz, a 1.8x bit rate of 9GHz, and a 5th harmonic of 12.5GHz. Except for Agilent DSO91304, which has a bandwidth of only 13GHz, which just meets the requirement of the 5th harmonic, Tektronix and LeCroy both have oscilloscopes with bandwidths above 12.5GHz, and Tektronix's oscilloscopes are more popular among board manufacturers.

SATA 3Gbps

SATA 3Gbps, commonly known as SATA 2, has a fundamental frequency of 1.5GHz, a 1.8x bit rate of 5.4GHz, and a 5th harmonic of 7.5GHz. It requires an oscilloscope with a bandwidth of 8GHz, which can be met by Agilent, Tekronix, and LeCroy.

DDR3 

DDR3 starts at 800MHz, and the highest that meets the specification is 1600MHz. X58 supports DDR3-1066 with a bandwidth of 8.5GB/S, a bit rate of 1.066Gbps, a fundamental wave of 533MHz, a 1.8x bit rate of 1.9188GHz, and a fifth harmonic of 2665. Agilent and Tektronix have both launched DDR3 test solutions.

USB 2.0 High SpeedUSB 2.0 can be said to be the entry-level high-speed serial bus, with a bit rate of only 480Mbps, a fundamental wave of 240MHz, a 1.8x bit rate of 864MHz, and a fifth harmonic of 1.2GHz. In fact, the USB certification organization believes that an oscilloscope with a bandwidth of 1GHz can meet the consistency test of USB2.0 High Speed.

In addition, the DMI bus between X58 and ICH10 is based on PCIE G2 x4, with a bandwidth of 2GB/s, which is similar to AMD's A-link interconnection between the north and south bridges (also based on PCIE G2 X4).

2. RD790FX

Compared with x58, AMD's competing product is RD790, and the most advanced one is RD790FX. 790FX natively supports 40 Lane PCIE G2, of which 32 lanes are allocated to graphics cards to form 2x16 and 4x8 crossfire, 6 lanes are allocated to peripherals, and the other 4 lanes form Alink to connect the north and south bridges.



The difference from X58 is that the CPU and RD790FX are connected via HT 3.0, and the memory only supports DDR2.


Dual-channel crossfire system

For standard high-speed serial buses such as PCIE, SATA, DDR, and USB, board manufacturers usually use Intel's Sigtest to test. Since Sigtest can analyze the waveforms captured by oscilloscopes from Agilent, Tektronix, and LeCroy, the oscilloscope is only used as a data acquisition card, which greatly reduces the dependence on the instrument (due to differences in eye diagrams and jitter analysis algorithms of oscilloscope manufacturers, the test results are inconsistent or not comparable). At the same time, sigtest can generate standard test reports, which are very popular among manufacturers. However, sigtest is not very suitable for debugging, because the data that can be analyzed by sigtest is limited, and the PLL bandwidth that can be set is also limited. It is only suitable for consistency testing of motherboards and graphics cards. The test interface is as follows: