diff --git a/mass-storage-gadget/.gitignore b/mass-storage-gadget/.gitignore
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+*.h
+boot.sig
diff --git a/mass-storage-gadget/README.md b/mass-storage-gadget/README.md
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+# USB mass-storage drivers for Compute Module 4
+
+This directory provides a bootloader image that loads a Linux
+initramfs that exports common block devices (EMMC, NVMe) as
+USB mass storage devices using the Linux gadget-fs drivers.
+
+This allows Raspberry Pi Imager to be run on the host computer
+and write OS images to the Compute Module block devices.
+
+## secure-boot
+If secure-boot mode has been locked (via OTP) then both the
+bootloader and rpiboot `bootcode4.bin` will only load `boot.img`
+files signed with the customer's private key. Therefore, access
+to rpiboot mass storage mode is disabled.
+
+Mass storage mode can be re-enabled by signing a boot image
+containing the firmware mass storage drivers.
+
+N.B. The signed image should normally be kept secure because can
+be used on any device signed with the same customer key.
+
+To sign the mass storage mode boot image run:-
+```bash
+KEY_FILE=$HOME/private.pem
+../tools/rpi-eeprom-digest -i boot.img -o boot.sig -k "${KEY_FILE}"
+```
+
+## Running
+To run load the USB MSD device drivers via RPIBOOT run
+```bash
+../rpiboot -d .
+```
+
+The activity LED will flash three times once the USB MSD
+devices have been initialised. A message will also be printed
+to the HDMI console.
+
+The UART console is also enabled (user 'root' no password)
+so that the user can login and debug the Compute Module.
+
+N.B. This takes a few seconds longer to initialise than the 
+previous mass storage implementation. However, the write speed
+should be much faster now that all of the file-system code
+is running on the ARM processors.
diff --git a/mass-storage-gadget/boot.img b/mass-storage-gadget/boot.img
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+++ b/mass-storage-gadget/boot.img
diff --git a/mass-storage-gadget/bootcode4.bin b/mass-storage-gadget/bootcode4.bin
new file mode 100644
index 0000000..55d735e
--- /dev/null
+++ b/mass-storage-gadget/bootcode4.bin
diff --git a/mass-storage-gadget/config.txt b/mass-storage-gadget/config.txt
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+# Load boot.img which contains usb.elf
+# In signed-boot or secure-boot mode the bootloader checks the
+# RSA signature of the ramdisk. The signature is located in boot.sig
+boot_ramdisk=1
+uart_2ndstage=1