nested transaction

Hello,

The new release includes savepoints, but I need to do a begin inside another begin and a commit/rollback after another commit/rollback.

For example, I have a pA procedure that update some data, so this procedure execute a begin, after manipulate data and ends with commit/rollback. pA procedure can to be called directly by the client aplication. In other hand, I have a pB procedure that also update some data and calls pA procedure, so pB procedure execute a begin, after manipulate data, after call pA procedure and ends with commit/rollback. pB procedure can also to be called directly by the client aplication.

The problem is that pA procedure can't do a new transaction, so what can I do?
Is possible to detect from pA that there is a transaction and so do a savepoint instead of a begin?

Thanks in advance,

pere