The Raspberry Pi SOC supports up to 2 PCM channels that it is described in BCM2835 datasheet page 119 which like below diagram
Therefore, we could expanse our 4 ports PiTDM to 8 ports PiTDM if we can use all of its 2 channels, that also means we are using 1 channel for 4 ports PiTDM right now :). The most important challenge is that we need to align the second channel to correct timing of 2M PCM highway. Fortunately, through a half month of hard work, we made it out and the 8 ports PiTDM module is going to release in next month 🙂
Here is a picture which is shown an 8 ports PiTDM is detected by the Digium GUI:
What is it can do of an 8 ports design?
Well, obviously, the 8 ports design can give you more ports which can expanse your PiTDM ability and capability, you can have 8 ports FXO connect to PSTN, or you can have 8 ports FXS connect to your phone or FAX machine.
Also, we can add the BRI module support as we have 8 pure 8bits PCM channels, certainly, we have the ability to support a BRI controller which means we can bring the Raspberry Pi to ISDN world.
The most famous and stable BRI controller is XHFC-4SU in the Asterisk world, here is it’s datasheet link http://www.colognechip.com/isdn/controllers/frame-xhfc-4su.htm
We built a new firmware which provides the PiTDM to work with Digium offical GUI which is faster and easy to use than Raspbx. It also support Pi 3 B+, Pi 3, Pi 2, B+, B and A models. You can download it in here. Here is a guide to show how to use it.
First of all, follow the Manual of installing PiTDM module in here to install the PiTDM module, when finished the PiTDM module’s installation, then download the firmware from the link that it is shown above.
Use the dd to copy it to a 4G at least SD card,
dd if=switchpi-digium-gui-1.0.1.img of=/dev/mmcblk0 bs=4M
When done, power up the Raspberry Pi with followed the Manual of installing PiTDM module in here. The default IP is 192.168.1.98, and the link is http://192.168.1.98:8088/gui/static/config/index.html. The GUI username is admin and password is admin, please change it to a stronger password when you log into the GUI.
The below picture shows how the Digium GUI detected a 2 FXS module and a 2 FXO module
We built a default SIP extension and one FXS channels that if you have FXS module installed which you can use it to test our PiTDM by quickly, it looks like below
Then you can create the default Dialplan and incoming calling rules or outgoing calling rules, and connect your PSTN cable to make the calls.
The SSH login default username/password is pi/raspberry.