$coupon->setType(Mage_SalesRule_Helper_Coupon::COUPON_TYPE_SPECIFIC_AUTOGENERAT‌​ED)->save();

 // Get the rule id

        $rule = Mage::getModel('salesrule/rule')->load(1);

        // Define a coupon code generator model instance

        // Look at Mage_SalesRule_Model_Coupon_Massgenerator for options

        $generator = Mage::getModel('salesrule/coupon_massgenerator');

        $parameters = array(

            'count'=>1,

            'format'=>'alphanumeric',

            'dash_every_x_characters'=>4,

            'prefix'=>'test',

            'suffix'=>'test2',

            'length'=>12

        );

        if( !empty($parameters['format']) ){

            switch( strtolower($parameters['format']) ){

                case 'alphanumeric':

                case 'alphanum':

                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_ALPHANUMERIC );

                    break;

                case 'alphabetical':

                case 'alpha':

                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_ALPHABETICAL );

                    break;

                case 'numeric':

                case 'num':

                    $generator->setFormat( Mage_SalesRule_Helper_Coupon::COUPON_FORMAT_NUMERIC );

                    break;

            }

        }

        $generator->setDash( !empty($parameters['dash_every_x_characters'])? (int) $parameters['dash_every_x_characters'] : 0);

        $generator->setLength( !empty($parameters['length'])? (int) $parameters['length'] : 6);

        $generator->setPrefix( !empty($parameters['prefix'])? $parameters['prefix'] : '');

        $generator->setSuffix( !empty($parameters['suffix'])? $parameters['suffix'] : '');

        // Set the generator, and coupon type so it's able to generate

        $rule->setCouponCodeGenerator($generator);

        $rule->setCouponType( Mage_SalesRule_Model_Rule::COUPON_TYPE_AUTO );

        // Get as many coupons as you required

        $count = !empty($parameters['count'])? (int) $parameters['count'] : 1;

        $codes = array();

        for( $i = 0; $i < $count; $i++ ){

            $coupon = $rule->acquireCoupon();

            $coupon->setType(Mage_SalesRule_Helper_Coupon::COUPON_TYPE_SPECIFIC_AUTOGENERATED)->save();

            $code = $coupon->getCode();

            $codes[] = $code;

        }

        return $codes;

    }