SIP calling

[bhupiister]

Have you tried SIP calling through this hat? Is this hat available for purchase?

[astuder]

As is, I don't think the Modem HAT can do SIP calling.

The chipset has an option for interfacing with the Skyworks Si3000 voice CODEC. However, that IC is not present on this HAT, nor are the necessary pins to interface with the CODEC broken out in the current version. I also don't know if SIP would be possible if the CODEC were present.

AN93 discusses integration with the CODEC in chapter 7.3, if you want to dig deeper.

That being said, adding the CODEC or at least breakout pins would be an interesting addition for future revisions.

I currently don't have the Modem HAT available for purchase, but plan to eventually make another batch. If you send me an email via the address on my profile, I can add you to my list of interested people and you will get a notification (no obligation to buy if you change your mind by then).

[astuder]

Though looking at this diagram from AN93, I think the CODEC is mainly about interfacing with a microphone and speaker. Making me wonder if there's a path for samples from the ISOMODEM (Si2457) to the Pi and vice versa.

[astuder]

..and digging a bit deeper in AN93, it may require a different chip (Si2494/2439) to use the voice features (see intro of chapter 7)

[bhupiister]

Hey sorry, completely missed your chat. So reading your messages, it seems possible but with a different chip right?

[astuder]

I'm not familiar with the details of SIP, so still not sure if that's the case. The above seems to be able to receive/send audio over the phone line, that's all.