unleashed-firmware/documentation/OTA.md

Executing code from RAM

In Flipper firmware, we have a special boot mode that loads a specially crafted system image into RAM and transfers control to it. System image executing in RAM has full write access to whole Flipper's flash memory — something that's not possible when running main code from same flash.

We leverage that boot mode to perform OTA firmware updates, including operations on radio stack running on second MCU core.

How does Flipper OTA work?

Installation of OTA updates goes through 3 stages:

1. Backing up internal storage (/int/)

It is a special partition of Flipper's flash memory, taking up all available space not used by firmware code. Newer versions of firmware may be of different size, and simply installing them would cause flash repartitioning and data loss.

So, before taking any action upon the firmware, we back up current configuration from /int/ into a plain tar archive on SD card.

2. Performing device update

For that, main firmware loads an updater image - a customized build of main Flipper firmware — into RAM and runs it. Updater performs operations on system flash that are described by an Update manifest file.

First, if there's a Radio stack image bundled with the update, updater compares its version with currently installed one. If they don't match, updater performs stack deinstallation followed by writing and installing a new one. The installation itself is performed by proprietary software, FUS, running on Core2, and leads to a series of system restarts.

Then updater validates and corrects Option Bytes — a special memory region containing low-level configuration for Flipper's MCU.

After that, updater loads a .dfu file with firmware to be flashed, checks its integrity using CRC32, writes it to system flash and validates written data.

3. Restoring internal storage and updating resources

After performing operations on flash memory, system restarts into newly flashed firmware. Then it performs restoration of previously backed up /int contents.

If update package contains an additional resources archive, it is extracted onto SD card.

Update manifest

Update packages come with a manifest that contains a description of its contents. The manifest is in Flipper File Format — a simple text file, comprised of key-value pairs.

Mandatory fields

Update manifest must contain the following keys in given order:

• Filetype: a constant string, "Flipper firmware upgrade configuration";

• Version: manifest version. Current value is 2;

• Info: arbitraty string, describing package contents;

• Target: hardware revision the package is built for;

• Loader: file name of stage 2 loader that is executed from RAM;

• Loader CRC: CRC32 of loader file. Note that it is represented in little-endian hex.

Optional fields

Other fields may have empty values, is such case updater skips all operations related to such values.

• Radio: file name of radio stack image, provided by STM;

• Radio address: address to install the radio stack at. It is specified in Release Notes by STM;

• Radio version: Radio major, minor and sub versions followed by branch, release, and stack type packed into 6 hex-encoded bytes;

• Radio CRC: CRC32 of radio image;

• Resources: file name of TAR acrhive with resources to be extracted on SD card;

• OB reference, OB mask, OB write mask: reference values for validating and correcting option bytes.

OTA update error codes

We designed the OTA update process to be as fail-safe as possible. We don't start any risky operation before validating all related pieces of data to ensure we don't leave the device in partially updated, or bricked, state.

Even if something goes wrong, Updater gives you an option to retry failed operations, and reports its state with an error code. These error codes have an [XX-YY] format, where XX encodes an operation that failed, and YY contains extra details on its progress where the error occured.

Stage description	Code	Progress	Description
Loading update manifest	1	13	Updater reported hardware version mismatch
		20	Failed to get saved manifest path
		30	Failed to load manifest
		40	Unsupported update package version
		50	Package has mismatching HW target
		60	Missing DFU file
		80	Missing radio firmware file
Checking DFU file	2	0	Error opening DFU file
		1-98	Error reading DFU file
		99-100	Corrupted DFU file
Writing flash	3	0-100	Block read/write error
Validating flash	4	0-100	Block read/write error
Checking radio FW	5	0-99	Error reading radio firmware file
		100	CRC mismatch
Uninstalling radio FW	6	0	SHCI Install command error
		80	Error awaiting command status
Writing radio FW	7	0-100	Block read/write error
Installing radio FW	8	0	SHCI Install command error
		80	Error awaiting command status
Radio is updating	9	10	Error waiting for operation completion
Validating opt. bytes	10	yy	Option byte code
Backing up LFS	11	0-100	Block read/write error
Restoring LFS	12	0-100	Block read/write error
Updating resources	13	0-100	SD card read/write error