diff --git a/src/libboard_artiq/src/cxp_downconn.rs b/src/libboard_artiq/src/cxp_downconn.rs
index e03329e..150189f 100644
--- a/src/libboard_artiq/src/cxp_downconn.rs
+++ b/src/libboard_artiq/src/cxp_downconn.rs
@@ -37,7 +37,12 @@ pub fn loopback_testing(timer: &mut GlobalTimer, speed: CXP_SPEED) {
         while csr::cxp::downconn_phy_rx_ready_read() != 1 {}
         info!("rx ready!");
 
-        cxp_proto::downconn_debug_send_trig_ack();
+        csr::cxp::downconn_phy_tx_stb_write(1);
+        cxp_proto::downconn_send_test_packet();
+        timer.delay_us(20000); // wait packet has arrive at rx
+        csr::cxp::downconn_phy_tx_stb_write(0);
+
+        // cxp_proto::downconn_debug_send_trig_ack();
 
         cxp_proto::downconn_debug_send(&cxp_proto::Packet::CtrlRead {
             addr: 0x00,
@@ -54,6 +59,7 @@ pub fn loopback_testing(timer: &mut GlobalTimer, speed: CXP_SPEED) {
         info!("after clr trig ack = {}", csr::cxp::downconn_trig_ack_read());
 
         info!("decoder error = {}", csr::cxp::downconn_decoder_error_read());
+        info!("test error = {}", csr::cxp::downconn_test_error_read());
         info!("packet type = {:#06X}", csr::cxp::downconn_packet_type_read());
 
         // TODO: investigate how to make my packet appear