Question M.2 E Key WiFi modules with UART/PCM interfaces and newer chipsets like Z690 or X570

[cinoI]

Hi

This is very special inquiry and I have already beaten my head against all schematics I could freely find, but was not able to come up with enough satisfiable information.

A lot of WiFi + BT combination M.2 modules these days come in an E key flavor, in which the Bluetooth part is not connected to the USB interface, but rather driven by UART and PCM. PCI-SIG explicitly lists UART and PCM/I2S as being supported in the E keyed pinouts.

FN-Link's 8291M-PR module thankfully provides schematics for the pinouts:


In there, it's clearly visible that BT is driven using pins [22 32 34 36] for UART and pins [8 10 12 14] for PCM.

PCI-SIG only provides schematics as a paid service, but thankfully manufacturers provide pinouts for their modules, like Congatec in their AN43 application notice:


In there, it's documented that the first PCIe x1 interface is connected to pins [47 49 41 43 35 37 55 53 52] and the second PCIe x1 interface to pins [71 73 65 67 61], which is probably true for most adapters (though the second interface might be connected to more pins for some).

That's all great, but how would I know if mainboards support these signals?

Most Z690- or X570-based mainboards come with a preinstalled E key WiFi module. Most often, but not always, that's an Intel AX200 or AX210 M.2, or sometimes a Mediatek (i.e., Ralink) MT7921K M.2 modules. Usually, both modules use PCIe for the WiFi part and USB 1.1 or 2.0 for the Bluetooth part, which can easily be provided by either E key M.2 slots or M.2 to PCIe adapters with additional USB support (a variety of such adapters already exist).
Then, some mainboards come with an Intel AX201 or AX211 module, which, as far as I know, only supports Intel's proprietary CNVi protocol and as such is only available for Intel-chipset-based mainboards.

That's great... but is there any way to know if chipsets (the mentioned two in particular, but also generally) support UART and PCM signals on the M.2 interface? The usual block diagrams aren't helpful (too coarse) and service manuals almost impossible to get, even if I wanted to. Having glanced over the M.2 specification, it doesn't look like PCM/I2S and UART interfaces are optional if E key support is implemented, but it also doesn't say that it's mandated. I know too well that board manufacturers love to take shortcuts and not implement things, even if that is outside of specifications, especially if nobody will ever notice because the missing functionality only affects more exotic interfaces that are rarely used.

And, lastly, even if all E key slots must always support the PCM/I2S and UART host interfaces (which would be great), is there any way to use multiple such cards if the mainboard merely provides one slot? I haven't seen any dual-E-key-slot mainboards yet. PCIe to NGFF/M.2 adapters fail to work on the UART + PCM/I2S side, since they only directly interconnect the PCIe pins to the physical PCIe connection. I guess I'm just out of luck when it comes to multiple of these modules? Ironically, using E-keyed modules which drive Bluetooth via USB works fine, since most (if not all) adapter cards come with additional pins that can be connected to standard USB 2.0 headers on the mainboard, but I have yet to see UART and PCM/I2S headers on mainboards - or adapter cards that expose such pins for an additional cable connection.

 

[hotaru.hino]

And this is the unfortunate thing about AMD: they don't supply any datasheets for their chips. Intel provides all sorts of nice technical documentation for their chipsets, CPUs, etc. But unless AMD hid them behind some developer account wall, I can't find anything that would explicitly say that the chipset itself at least supports the signals you're looking for. However, my instinct is going to say that no, the chipset doesn't have those lines hooked up because it's expected that the motherboard manufacturer will install a Wi-Fi card with the motherboard, and PCIe/USB makes the most sense in a PC environment.

The card you're looking at, judging by what the manufacture says, appears to target embedded systems:

Applications

OTT/IPTV/DVB/Set-top Box, Tablet PC, Advertising Machine,Intelligent TV, IPC/NVR, Industrial Control Equipment,Car Recorder,Intelligent Doorbell, Intelligent Projector, Virtual Reality, VR/AR, Wireless Storage, Printer, POS Machine, Electronic Scale,Vehicle Front/Rear End, Drone, Robot, HDMI Transmitter,Smart Gateway, Education,Toys, Lighting Lamps, Intelligent Street Light, Intelligent Home Appliances/Home Appliances Instrumentation (Water, Electricity, Gas), Smart City and other Consumer Electronic Products.

 

[cinoI]

And this is the unfortunate thing about AMD: they don't supply any datasheets for their chips. Intel provides all sorts of nice technical documentation for their chipsets, CPUs, etc.

I'd be happy to get technical information for Intel's Z690 chipset, but haven't been able to find anything but very coarse block diagrams. On the mainboard I'm interested in, the WiFi M.2 slot is directly attached to the Z690 chipset, so if you know of any decent technical documentation regarding pinouts (or possibly more), that would be highly appreciated. I've tried to do my homework as best as I was able to.

I'm still torn between AMD and Intel, both have their pros and cons. Intel builds are a bit more expensive, but at the very last I don't factor them out any longer, since DDR5 with on-chip-ECC nowadays is a somewhat decent alternative to full ECC DDR4 RAM as can be used with AMD hardware (signal lines usually don't go bad and are only very rarely struck by high-energy particles, while the RAM modules themselves almost always deteriorate over time). My main goal is to get pinout information regarding the WiFi M.2 slot and respective capabilities to make an informed buying decision, with both options being open.

However, my instinct is going to say that no, the chipset doesn't have those lines hooked up because it's expected that the motherboard manufacturer will install a Wi-Fi card with the motherboard, and PCIe/USB makes the most sense in a PC environment.

Possibly, yes, I can't rule that out. USB interfaces are readily available in laptop and desktop PCs, but highly specialized embedded systems might want to skip on USB support if not necessary. Serial interfaces (UART) are practically always used and combing that with a cheap DAC for PCM/I2S support is likely the less expensive and invasive alternative. That said, these components are also standard on desktop and laptop PCs (even if just internally), so I wouldn't rule out that E-keyed M.2 slots are hooked up to these interfaces even on PCs. I just don't own any new mainboard, so can't test (at least just yet).

The card you're looking at, judging by what the manufacture says, appears to target embedded systems:

Heh, Fn-Link is... let's say creative in their marketing. They will tell you whatever you want to hear if that makes their product attractive to you. To be fair, though, I do have 10 of these modules stashed away and at least the WiFi part (which is driven by standard PCIe; couldn't test the BT part of course) worked fine during my short testing marathon. It would be a shame to let them go to waste and I can't sell them off for legal reasons. The QCA6391 chip is decent and impressive in AP mode with its simultaneous dual band capabilities.

 

[cinoI]

I'd be happy to get technical information for Intel's Z690 chipset, but haven't been able to find anything but very coarse block diagrams.

... unless you look in the right place, namely technical resources for 12th generation core processors, which also includes a document for the 600 series PCH.

In there, we find chapter 33.0, which describes Connectivity Integrated (CNVi), but also mentions Discrete Connectivity (CNVd) functions (which is the part that really interests me), and table 33.2 looks very promising, quoting:

GPP_D5 / CNV_RF_RESET#

For discrete connectivity with UART host support: Optional Bluetooth*
I2S bus sync

GPP_J2 / CNV_BRI_DT / UART0_RTS#

For discrete connectivity with UART host support: Bluetooth* UART RTS#
[...] other UART pins

This gets my hopes up that the PCH actually supports UART and PCM/I2S host interfaces. All UART pin functions are documented in that table, minus the WAKE signal (though that might well be optional, since it sounds like an outgoing wakeup signal to the host). For PCM/I2S, there's only the bus sync function, while CLK, IN and OUT seem to be missing, which is probably explainable by this description:

Only the digital part of the connectivity function is located in Connectivity Controller cores, while the CRF cores handle some digital, but mostly analog and RF functionality. Each core in the Connectivity Controller has an interface to the host and an interface to its counterpart in CRF. CRF cores include an analog part which is connected to board level RF circuitry and to an antenna.

The analog part (which is PCM/I2S) is thus probably handled mostly in the module and not specified in the document.

That sounds great indeed. It might just work the way I'd like to have it. Not for additional modules, of course, but the specification looks promising.

Thank you for nudging me in the right direction, highly appreciated!

And, yes, technical data for AMD chipsets is almost impossible to get. The only document released in 2021 was the RAIDXpert2 user guide, which is totally useless to me. I might ask AMD directly, but my hopes aren't high up on even getting an answer.