DCSD Cable



The DCSD Alex cable is used in factories to communicate over serial to run tests and write to the SysCfg (for serial definitions, etc) during production. These cables are produced by Shenzhen Alex Connector Co. Ltd. in China. They can be purchased from obscure markets. There are two known types of DCSD cable. An older one, with lights and only one USB female USB connector, and a newer model, which lacks lights, and has two female USB connectors.

Other notes

 * The Lightning Connector has a specific Accessory ID flashed to it for enabling serial via the Tristar chip.
 * This PCB is quite easy to replicate, but without the proper Accessory ID you will need to mimic the protocol similar to how key2fr did in his research.
 * In theory, you can use the Tristar for JTAG through a similar board, but JTAG gets disabled by the device during boot due to production fusing status.

Verbose Boot
One use of the cable was to view verbose boot. You could access this by setting Debug-uarts_(iBoot_variable) in iRecovery or nvram, however, since iOS 9, this output has been obfuscated.

Shell over serial
Using qwertyoruiopz's serialsh, it is possible to get shell over serial. This is useful, because it does not require any additional daemons other than those shipped with iOS. An example use case for this would be protecting against bootloops.

Debugging the kernel
Using the DCSD cable, it is possible to attach GDB to the iOS kernel, and pause it's running.