add device tree overlay instructions, and update Day release notes
bug: 143627524
Change-Id: Ic5999230c22f2858d183c453d7d01f2314901602
diff --git a/DeviceTreeOverlays.md b/DeviceTreeOverlays.md
new file mode 100644
index 0000000..f1ae8a7
--- /dev/null
+++ b/DeviceTreeOverlays.md
@@ -0,0 +1,60 @@
+# Device tree overlays
+
+The uboot script on Mendel is configured to load device tree blob (`.dtb`) files from `/boot/` and
+overlay the existing device tree with any `dtb` files specified in the `/boot/overlays.txt` file.
+
+For example, you can use the following steps to increase the CMA size to 512 MiB
+(default is 320 MiB). (All steps are performed on your Mendel device.)
+
+First, create your device tree source (`.dts`) file (in this example, named `cma512.dts`):
+
+```
+// Set CMA region to 512M
+/dts-v1/;
+/plugin/;
+
+/ {
+ compatible = "fsl,imx8mq-phanbell";
+
+ fragment@0 {
+ target-path = "/";
+ __overlay__ {
+ reserved-memory {
+ linux,cma {
+ size = <0 0x20000000>;
+ };
+ };
+ };
+ };
+};
+```
+
+Install the device tree compiler:
+
+```
+sudo apt-get update
+
+sudo apt-get install device-tree-compiler
+```
+
+Compile your `dts` file to `dtb` format:
+
+```
+dtc -I dts -O dtb -o cma512.dtbo cma512.dts
+```
+
+Move the `cma512.dtbo` file into `/boot/` and edit the `/boot/overlays.txt` file (as root) to
+include this new file. The `overlays.txt` file should then look like this:
+
+```
+# List of device tree overlays to load. Format: overlay=<dtbo name, no extenstion> <dtbo2> ...
+overlay=cma512
+```
+
+Then reboot and you're done. You can verify the CMA update like this:
+
+```
+cat /proc/meminfo | grep CmaTotal
+```
+
+It should print `524288 kB`.
\ No newline at end of file
diff --git a/Releases.md b/Releases.md
index 9428b75..04c8f7f 100644
--- a/Releases.md
+++ b/Releases.md
@@ -2,6 +2,8 @@
This is a non-exhaustive summary of changes included in each version of Mendel.
+To check your Mendel version, run `cat /etc/mendel_version`.
+
For system image downloads, see [coral.ai/software](https://coral.ai/software/).
@@ -15,8 +17,8 @@
new SecureBoot and AppArmor changes do not apply to Mendel)
+ Support for Python 3.7
+ Support for OpenCV and OpenCL
++ Support for device tree overlays
+ Upgraded GStreamer pipelines
-+ Improved stability for memory timing
+ Upgraded Linux Kernel (4.14)
+ Upgraded U-Boot bootloader (2017.03.3)
