The Raspberry Pi 4 features a Broadcom BCM2711 processor with Cortex-A72/A53 cores that makes it competitive against other SBC’s based on Rockchip RK3399 or Amlogic S922X/A311D processors. The new processor also happens to have a PCIe interface, but it’s not exposed on the board since the interface is used by VIA VL805 PCIe USB 3.0 controller for the four USB 3.0 ports on the little computer.
At the time, we expected the PCIe interface to be exposed in future Raspberry Pi boards or a Raspberry Pi Compute Module 4. But some people did not feel like waiting and instead hack the Raspberry Pi 4 SBC to access the PCIe interface. That hack is clearly not for everyone though…
But based on a recent interview of Eben Upton with Tom’s Hardware we got pretty much confirmation that the Raspberry Pi Compute Module 4 will be coming next year, and expose PCIe signals through the edge connector.
The Raspberry Pi Compute Module, CM4, we will support NVMe to some degree on that, because of course, it has a PCI Express channel.
…We have a single lane Gen 2 which is used to supply USB 3 on the Raspberry Pi. On the module that would be exposed to the edge connector and we’re likely to support NVMe over that..
PCIe will be exposed, but it looks like support for NVMe storage is still to be determined. Also don’t expect to be able to connect a PCIe graphics card since most PCIe implementations in Arm processors would not support it due to limitations such as maximum addressable memory as is the case for Rockchip RK3399.
Tom’s hardware further asked where a future Raspberry Pi board might have PCIe support via an M.2 socket for example. Based on Eben answer it will most likely not happen:
In the core product, maybe a future Raspberry Pi may pick up something, but it is challenging. It is not without cost, both in terms of the silicon and in terms of the connector, as the connectors are not free. Also providing board area for the connectors, if you look at the Raspberry Pi there’s obviously not room for an M.2 slot”
…What would a 4A look like? We have a decision to make about what we do with the USB 2. The USB 2 on Pi 4 is brought to the power jack, the OTG is brought to the power jack so we’d have a question in our minds about whether we undid that, probably, as we do on other A boards [and] brought it to the right-hand edge as a single connector”
You can watch the full interview in the video below.