I think, I wasn't be clear in the post I will ask again.
I have to do project, it is complicated a little bit. The project has two parts and it is a communication project.
The First part is about make VoIP system using Raspberry PI as a system server and I have to make FXO interface by myself. I made it by using SI3050 and SI3019 ICs. I don't have a problem in this part.
Note before read second part: in my country we use ADSL over POTS.
The second part is about get POTS line and connect it to Raspberry, the same one in the first part, and use Raspberry as a DSP for process ADSL signal. I know that I can't conect POTS line directly to Raspberry and I have to use interface for this. And I search about using Raspberry as a DSP, I found that we can't use it for many reasons but we can used it only for simple DSP operations.
know my question is can Raspberry used as DSP for ADSL? and if it possible, can Raspberry do multi tasks? in this project it will be a VoIP server and DSP for ADSL.