I've not heard of anyone using this chip for dtmf.
Considering the number of dtmf chips on the market the use of a 128 pin dsp chip is a bit of an overkill.
A search on google for adsp2181 brings up a lot of hits. If noboby is able to help you then I would suggest that you just sit down and browse the web to try and find the information you want.
One question. How far have you got with the project?