Update Hardware M2 page

docs/helios64/m2.md

@@ -1,30 +1,32 @@
-M.2, formerly known as the Next Generation Form Factor (NGFF), is a specification for internally mounted computer expansion cards and associated connectors.
+M.2 formerly known as the Next Generation Form Factor (NGFF) is a specification for internally mounted computer expansion cards and associated connectors. The M.2 replaces the mSATA standard.
-M.2 replaces the mSATA standard, which uses the PCI Express Mini Card physical card layout and connectors.
 
-Supported bus in the Helios64 M.2 interface is SATA and USB 2.0.
+Helios64 provides an M.2 interface (J2) to connect the following expansion cards:
 
-!!! Warning
+* M.2 SATA SSD
+* M.2 USB2.0 modules (e.g NPU extension).
+
+![M.2 Location](/helios64/img/m2/m2.jpg)
+
+!!! Important
 		PCIe SSD is not supported.
 
----TBU---
+## Form Factor and Keying
 
-## Location
+The M.2 connector (J2) is Key-B which is compatible with most of M.2 SATA SSD of Key-B or Key-M+B Key form factors.
 
-Helios64 support M.2 device on header P2 which is located next to SATA 1 connector.
+![M.2 Keying](/helios64/img/m2/m2_keying.jpg)
-You can refer to the connector/interface list at [hardware overview](/helios64/hardware#connector-interface-list) page.
-The location of the M.2 socket is shown in below figure:
 
-![M2 Pinout](/helios64/img/m2/m2-zoom-w-symbol.jpg)
+The board provides mounting holes for 2260 and 2280 cards.
 
-## Size
+![M.2 Form Factor](/helios64/img/m2/m2_form_factor.jpg)
 
-The maximum size of supported M.2 device is the 2280 size. 
+## Usage
 
-## Notes related to M.2 Card
+The M.2 interface on Helios64 only supports SATA 3.0 and USB 2.0 buses.
-The M.2 devices installed in Helios64 is configured as sharing devices with SATA Port 1.
-Therefore if you install M.2 SATA module, you will not be able to access the SATA Port 1.
-In another case, if you use the M.2 USB module, the SATA Port 1 still accessible from the system.
 
-The USB bus is connected to the [OHCI/EHCI Host 0](/helios64/usb/#usb-on-helios64).
+The M.2 SATA bus is shared with SATA Port 1. Therefore if you install an M.2 SATA SSD card, SATA Port 1 (J3) will automatically get disabled. But if you use the M.2 interface for USB modules, the SATA Port 1 (J3) is still enabled and accessible by the system.
 
-The M.2 socket in the Helios64 board may NOT support USB modem (WWAN), because the USB modem requires the SIM Card connection and another signal.
+For more details refer to [SATA page](/helios64/sata/).
+
+!!! Note
+		The M.2 interface on Helios64 may NOT support USB modem (WWAN) because USB modem often requires external SIM Card connection and other signals.