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manawyrm, 11/21/2022 03:12 PM

Gigaset C430 Hacking


The C430HX/A phones use a Dialog/Renesas SC14441 SoC, which is a fully integrated DECT handset IC, with all peripherals built in.
The firmware is stored on an external Quad-SPI flash chip (MX25U1635E), 2 MByte.

The CPU inside the SC14441 is a CompactRISC CR16c plus-architecture.


The firmware can be modded by unsoldering the SPI flash chip and flashing it in an external programmer (like a MiniPro TL866):


Be careful when trying to flash the SPI flash in-circuit! The phone runs at 1.8V I/O voltage! Do not apply 3.3V to any parts of the system externally!

The SPI flash IC is being accessed at 82.944MHz, using Quad-SPI.
Trying to run jumper wires from the SOIC footprint out to an external socket can be accomplished, but needs to be done very carefully, ideally with shielded wires, kept as short as possible. Even with a pretty reasonable setup, the phone will be unstable in this configuration.
It might be possible to lower the SPI clock frequency to a more reasonable value somehow.


Not much info is available about the SC14441 (except for a single page overview), but a datasheet for the similar SC14480 SoC is floating around online.
The SC14480 has many of the same registers and peripherals and the register maps are highly useful for looking at the SC14441/C430 firmware.

Gigaset also offers a GPL download .tar.gz for another product from their DECT lineup for one of their DECT base stations, which is running GPL software.
This tarball contains a full GNU toolchain and a bunch of other interesting things:

Ghidra can decompile the firmware image for the phones with the cr16c architecture.
You'll need to map the flash memory at 0xF0000 and some volatile peripheral registers at 0xFF4000 - 0xFFC00.
Ghidra memory map setup


Custom ringtones

Ringtones on the C430 phones are standard MIDI files, being played by a software MIDI synthesizer implementation.
This implementation seems to be called "Sitel Midi Player", but no further info about that player/synth is publicly available.


A video showing the custom ringtones is available on YouTube:

The MIDI files are embedded into the firmware directly and can be found by looking for the MIDI header magic "MThd" (ascii).
From there the amount of tracks and then their length in bytes can be determined by looking at the MIDI track headers.

This script will look at a binary dump and extract any MIDI files (this script is not limited to Gigaset phones, useful in general):

Running that script will result in a folder full of MIDI files like this:

[gigaset-c430-modding]$ file *
extract-1662195.mid:    Standard MIDI data (format 0) using 1 track at 1/480
extract-1662318.mid:    Standard MIDI data (format 1) using 1 track at 1/480
extract-1662352.mid:    Standard MIDI data (format 0) using 1 track at 1/480
extract-1662462.mid:    Standard MIDI data (format 1) using 1 track at 1/480
extract-1662510.mid:    Standard MIDI data (format 1) using 1 track at 1/240

The number in the filename is the offset of the MIDI file in the dump, in decimal notation.

As MIDI files are read from the start and contain their own length information, these files can be replaced by files that are the exact same length or shorter.
When trying to replace a ringtone, find a suitable stock ringtone and just replace the bytes starting at the same offset with your desired .mid file.
Take great care not to overwrite any other memory content (by overstepping the boundaries of the stock MIDI files, etc.), as this will lead to memory corruption and crashes.

An example shell script for modding 6 custom ringtones into the firmware can be found here:

This script also uses dd to patch the strings of the ringtone names. When doing this, ensure you don't overwrite the \0 null terminator, otherwise you'll end up with memory corruption again. wqdiyzjfpvk.png

Creating/editing MIDI files to fit onto the phone can be done with a free/open tool like "Rosegarden". The exported MIDI files seem to be very compatible with the Sitel player.

Ni-MH battery charge configuration

Files (7)
IMG_2138.JPG View IMG_2138.JPG 759 KB Gigaset C430HX internal PCB manawyrm, 11/21/2022 02:12 PM
IMG_6053.JPG View IMG_6053.JPG 1.85 MB MiniPro TL866 programmer, with ZIF socket manawyrm, 11/21/2022 02:12 PM
xocetzhvijs.png View xocetzhvijs.png 16.8 KB Ghidra memory map setup manawyrm, 11/21/2022 02:38 PM
cgpmjvoeitb.jpg View cgpmjvoeitb.jpg 398 KB C430, showing the custom "nyan" ringtone manawyrm, 11/21/2022 03:10 PM
wqdiyzjfpvk.png View wqdiyzjfpvk.png 9.56 KB Hex editor, showing the string literals for all ringtones manawyrm, 11/21/2022 03:12 PM
hgtedmkcrfq.jpg View hgtedmkcrfq.jpg 2.95 MB battery voltage and current, stock firmware manawyrm, 11/22/2022 01:38 AM
dwbaefchmtk.jpg View dwbaefchmtk.jpg 2.81 MB battery voltage and current, modded firmware manawyrm, 11/22/2022 01:38 AM

Updated by manawyrm over 1 year ago · 4 revisions

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