This M.2 2280 M-key card allows you to reclaim SATA ports that your motherboard may have as part of the chipset, but are not broken out to SATA connectors since the chipset shares their pins with the M.2 slot's PCI Express lanes.
Each SATA port is connected to a data lane of the M.2 card, although not all motherboards and M.2 slots support more than one SATA port (lane 0); if you just want one port, this adapter can work, but there are off-the-shelf ones that will also do the job. Read on for compatibility information.
I am not going to be offering assembled boards for the foreseeable future, since shipping from Brazil is too expensive and takes too much paperwork. You can order boards from your PCB vendor of choice (Gerber files are in the gerbers directory) and assemble them yourself (no SMD work is required); make sure the PCB thickness is 0.8mm and the total size is 22mm x 80mm, and go for ENIG finish if possible for best signal integrity (standard HASL finish is untested).
The only BOM item is a vertical through-hole SATA data connector, quantity 1 to 4 according to your needs. I've had success with LCSC part C2926857, though replacements can be easily found, or even desoldered from a donor board. When considering a replacement, make sure its retention pins are centered (aligned with the data pins); some parts have one of the retention pins slightly offset.
This adapter is expected to work (i.e. provide access to more than one SATA port) on a SATA+NVMe M.2 slot on the motherboard platforms listed below. Note that actual compatibility is at your own risk; boards might use an external switch chip to route only a single SATA port to the M.2 slot, or they might not have the SATA/PCIe mode switching signals hooked up for all lanes, or the BIOS might not enable normally-unused SATA ports.
In my limited real world testing with the ASUS H170-PLUS D3 (2 SATA ports routed to a single M.2), a drive attached to the second port was not visible in BIOS menus, but it was still initialized by the BIOS and detected by the operating system.
- Chipsets:
- AMD B550: Up to 2 ports (0 and 1) from a slot connected to the chipset ("Group 2" - second set of PCIe lanes).
- AMD X570, 600 series: Up to 4 ports from a slot connected to the chipset (combo lanes: X570, B650, X670).
- Intel 300/400 series: Up to 4 ports from a slot connected to the chipset (HSIO lanes 14-17, 28-21 or 22-25).
- Intel 500/600/700 series: Up to 4 ports from a slot connected to the chipset (HSIO lanes 22-25, 26-29 or (500 only) 30-33).
- Older stuff: Some older motherboards which hijack multiple chipset SATA ports for M.2 can make use of this adapter. One example is the aforementioned ASUS H170-PLUS D3, which only exposes 4 of the 6 SATA ports provided by the H170 chipset, with the remaining 2 routed to M.2 slot lanes 0 and 1.
- CPUs:
- AMD AM4: Up to 2 ports (0 and 1) from a slot connected to the CPU. Note that most motherboards already expose these (2 SATA ports shared with the CPU M.2 slot), making this adapter redundant.
One quirk of SATA is that its B (receive) differential pair has a different polarity than that of the A (transmit) pair or PCI Express RX/TX pairs, and unlike most PCIe implementations, it does not tolerate polarity inversion. Since the chipset's SerDes expects the same lane polarities in both SATA and PCIe modes, motherboards account for this quirk by inverting the polarity of the first SATA/PCIe lane going to the M.2 slot, to satisfy both SATA (cannot be inverted) and PCIe (can be inverted):
| M.2 pin | PCB | Chipset pin |
|---|---|---|
| PCIe TX0+ or SATA A+ | 🡸 | PCIe TX0+ or SATA A+ |
| PCIe TX0- or SATA A- | 🡸 | PCIe TX0- or SATA A- |
| PCIe RX0+ or SATA B- | 🡾 | PCIe RX0+ or SATA B+ |
| PCIe RX0- or SATA B+ | 🡽 | PCIe RX0- or SATA B- |
| PCIe TXn+ | 🡸 | PCIe TXn+ or SATA A+ |
| PCIe TXn- | 🡸 | PCIe TXn- or SATA A- |
| PCIe RXn+ | 🡺 | PCIe RXn+ or SATA B+ |
| PCIe RXn- | 🡺 | PCIe RXn- or SATA B- |
Since I have yet to see a motherboard which inverts the RX polarity on all lanes (not just lane 0), this card inverts it on lanes 1-3 so that they can work properly in SATA mode. If you get connection errors (Linux dmesg: SATA link down (SStatus 1 SControl 300)) on ports 1-3 even with high quality cables, you somehow have a motherboard which also inverts lanes 1-3; if you're feeling adventurous, the jumperable branch has a special variant of this card with jumper links to configure RX polarities at will.
Huge thanks to Arya for helping me with the design (using their nvme_to_dual_ssd card as a base) and prototyping of this project.