Description
Due to a bug in Quartus® II Software version 12.0, tx_digitalreset does not have an effect in Stratix® V GX devices.
After the completion of offset cancellation, the tx_digitalreset signal is stuck de-asserted and cannot be controlled by the user.
Resolution
To work around this problem you should install Quartus II software patch 12.0 dp2 which is available from the link below.
Quartus II 12.0 Software patch dp2