doc: Point out that FAT partition must be unmounted for FDT extraction to work

1 files changed, 3 insertions, 2 deletions

diff --git a/README.md b/README.md
index bbe64d0..c89f331 100644
--- a/README.md
+++ b/README.md
@@ -137,7 +137,7 @@ qemu-system-riscv64 -M virt -m 2G -display none -serial stdio -bios /path/to/u-b
 ### Extract QEMU device tree
 
 The default `arch/riscv/dts/qemu-virt64.dtb` tree is an image tree and doesn't help.
-To extract the device tree, create an empty file on the disk image.
+To extract the device tree, create an empty file on the disk image *and unmount it*.
 Then boot the VM as explained above but hit a key before it autoboots.
 Run the following command in the U-Boot shell:
 
@@ -160,7 +160,8 @@ virtio scan
 fatwrite virtio 0 0x<ENV_OUTPUT> <EMPTY_FILE_NAME> <HEX_TOTALSIZE>
 ```
 
-You can now `poweroff` and build an image using the commands above.
+You can now `poweroff`, mount the partition again and build an image
+using the commands above.
 
 # Boot protocol