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Gen 4 PCIe Switch for ADAS Applications

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Microchip Technology recently announced the industry’s Gen 4 automotive-qualified PCIe switches, delivering low latency and high bandwidth required to link the CPU and accelerator building blocks used in ADAS applications.

PCI Express (PCIe) has been successfully employed for years in the data center market, where high-speed data transfer and reduced latency are imperative. This is mainly due to the scalability, through multi-lane links, of the PCIe devices, along with their backward compatibility, and to the support provided by different operating systems, software, and drivers.

For the same reasons, PCIe is emerging as the preferred computer interconnect solution in the automotive industry too, providing ultra-low latency and low-power bandwidth scalability to CPUs and specialized accelerator devices. The new Switchtec Gen 4 PCIe devices enrich Microchip’s broad portfolio of PCI Express switches, addressing the ADAS requirements for high-speed connection supporting distributed and real-time safety-critical data processing.

“At Microchip, we’ve been working for five years to automotive-qualify our Gen 4 PCIe switches. Autonomous driving systems use CPU, GPU or SOC, that have Gen 4 PCIe interface for mission-critical applications. That’s the reason why we decided to automotive qualify our Gen 4 switches”, said Krishna Mallampati, director of marketing and applications for PCIe switch products at Microchip, in an interview with EE Times.

PCIe Switch

The key factors of the Switchtec Gen 4 PCIe switch family can be summarized as follows:

  • High speed interconnect: Gen 4 PCIe devices feature a 2x speed (16 GT/s) compared to previous generation switches. This is essential for autonomous driving applications, which require data to be transmitted as fast as possible in order to make decisions in a short time
  • Low latency: Gen 4 PCIe switches have the value of 110 ns pin-to-pin
  • Scalability: the Switchtec family includes products with up to 28-, 36-, 52-, and 100-lanes (up to 52 for the automotive-qualified version). That means high scalability since customers can switch from one device to another, building up to 52 connections
  • Comprehensive diagnostics and debugging: all devices support Microchip’s ChipLink, a tool that provides a diagnostics and debugs facility for the customers.

“This is our Gen 4 PCIe switch product family, which we has been shipping for five years and we have been winning big in the data centre. Autonomous driving is also called as data centre on wheels. So, what we did was to take all those data centre features and few things and proceeded with standard automotive testing to be automotive qualified,”said Mallampati.

The AEC-Q100 Grade 2 automotive qualification has more stringent requirements, such as -40°C to +105°C ambient operating temperature range, tri-temperature test, production burn-in, and system-level testing.

“These are tests that we do on our chips before we ship them to the customers so that they are assured that we’re doing all the quality and reliability test. After that, the customers will perform their own test for their entire chassis and for their entire car, as well”, said Mallampati. Switchtec automotive-qualified switch portfolio is shown in Figure 1.

Switchtec automotive-qualified switch family
Figure 1 Switchtec automotive-qualified switch family

It includes three swim lanes: a fanout switch, a programmable switch, and a fabric switch. The important thing is that all of them share the same package size which allows easy scalability. According to Microchip, the main idea was to offer the customers a firmware that looks at the specific part number and then enables only the appropriate features. That adds also flexibility since the customers don’t have to make any hardware changes, they can just upgrade or downgrade their designs switching from one part number to another inside the same family. Only the firmware needs to be updated.

An example of an application is shown in Figure 2. We can think of it as the easiest way to use a PCIe switch, where the customers could initially use it for interconnecting devices (fanout feature). By providing the product’s API, Microchip enables customers to make modifications to the behavior of the PCIe switch. In this way, they can add their own specific functionalities. That is basically the high-level difference between the fanout switch, the programmable switch, and the fabric switch.

In the example of Figure 2, there is one SSD connected to the PCIe switch, plus other four devices, each of which implements a specific capability through a SoC, a CPU, or a GPU. All four of them are sharing the same and unique SSD. That is a feature that is only possible with this kind of product. And this feature is something that is very interesting in autonomous driving, where an SSD could be used as a sort of black box. The block diagram shown in Figure 2 is a typical example of automotive centralized network which reduces both system complexity and cost by using a centralized compute platform.

PCIe switch used for moving data between high-performance SoCs
Figure 2: PCIe switch used for moving data between high-performance SoCs

Suppose we have an autonomous car where the driver is not paying attention and there is a malfunction, or, even worse, there is an accident involving the autonomous car. The SSD storage device, acting as a black box, stores all the relevant data so that, in case of an issue, all the investigating authorities can take the data from the SSD, determining what the conditions were prior to the issue. In order for that to work, the SSD must be able to allow read and write from all four hosts. That is exactly what the PCIe fabric switch does. We could also take any SR-IOV endpoint and enable multiple hosts to share the same SSD. There is only one resource, the SSD, but virtually each host will be able to take a slice of it.

“Another advantage with this approach is that car manufacturers might decide to up sell or down sell their different car models based on the features that they offer. Their hardware would not change, but since we have so many options for a PCIe switch, an automotive vendor or car manufacturer might include certain features and set a different price level, or reduce the features and set a lower price level”, concluded Mallampati.

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