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digicom:digicom

Digicom Router USB hack

I bought a Digicom ADSL router for 30€ (RAW304G-T07).

It is based on BCM96318 Broadcom chipset. It accepts Telnet connections and runs BusyBox v1.17.2.

# cat /proc/cpuinfo 
system type             : 96318REF
processor               : 0
cpu model               : Broadcom BCM3302 V3.3
BogoMIPS                : 331.77
# cat /proc/version 
Linux version 2.6.30 (root@localhost.localdomain) (gcc version 4.4.2 (Buildroot 2010.02-git) ) #5 Thu Nov 26 18:19:11 CST 2015

The interesting feature (for that price) is that it has an USB port for sharing a printer or a USB storage key among the users of the LAN.

So I bought a 2TB USB HDD… just to find out that the USB port does not deliver enough energy for an HDD. Considering that the router has a wall power supply there are no reasons to believe that it could not provide the required current. So… hacking time.

I opened the router and, with a multimeter, I found out that the +5V required by the USB are provided by a small IC, located between the power connector and the USB connector.

I could not find the specification/datasheet of this device (the only marking is HS6SA). However I discovered that it has two 5V outputs. One connected to the USB connector, and one just left disconnected because of an unpopulated resistance (R89).

My 6th electronic sense told me to short-circuit the two 5V rails and.. BINGO ! Once plugged in, the USB HDD starts to spin !

Explanation

First of all… I don't have an explanation. Just some hypothesis.

In the Raspberry Pi, the USB port current limit is provided by a particular device: the AP2253 current-limiter power switch. The maximum current can be set with some external tuning resistors. More details here: http://hackaday.com/2015/04/06/more-power-for-raspberry-pi-usb-ports/.

I suspect that the small device (HS6SA) inside my router is something similar. By shorting R89 I have probably by-passed this mechanism, which is exactly what I wanted.

For the moment, it works very well (no excessive overheating or system instability) even with high-load (ex. streaming a film from the HDD wirelessly).

digicom/digicom.txt · Last modified: 2016/11/23 23:37 by dainaccio