diff --git a/src/libboard_artiq/src/cxp_downconn.rs b/src/libboard_artiq/src/cxp_downconn.rs
new file mode 100644
index 0000000..2086fbe
--- /dev/null
+++ b/src/libboard_artiq/src/cxp_downconn.rs
@@ -0,0 +1,89 @@
+use embedded_hal::prelude::_embedded_hal_blocking_delay_DelayUs;
+use libboard_zynq::{println, timer::GlobalTimer};
+use log::info;
+
+use crate::{cxp_phys, pl::csr::CXP};
+
+pub fn loopback_testing(channel: usize, timer: &mut GlobalTimer, speed: cxp_phys::CXP_SPEED) {
+    println!("==============================================================================");
+    cxp_phys::change_linerate(speed);
+
+    unsafe {
+        info!("waiting for tx&rx setup...");
+        timer.delay_us(50_000);
+        info!(
+            "tx_phaligndone = {} | rx_phaligndone = {}",
+            (CXP[channel].downconn_txinit_phaligndone_read)(),
+            (CXP[channel].downconn_rxinit_phaligndone_read)(),
+        );
+
+        // enable txdata tranmission thought MGTXTXP, required by PMA loopback
+        // (CXP[channel].downconn_txenable_write)(1);
+
+        info!("waiting for rx to align...");
+        while (CXP[channel].downconn_rx_ready_read)() != 1 {}
+        info!("rx ready!");
+
+        // cxp_proto::downconn_send_test_packet(channel);
+
+        // FIXME: why test + trig ack doesn't work well for rx??
+        // cxp_proto::downconn_debug_send_trig_ack(channel);
+
+        // const DATA_MAXSIZE: usize = 253;
+        // let data_size = 4; // no. of bytes
+
+        // let data: u32 = 0xDADA as u32;
+        // let mut data_slice: [u8; DATA_MAXSIZE] = [0; DATA_MAXSIZE];
+        // data_slice[..4].clone_from_slice(&data.to_be_bytes());
+        // cxp_proto::downconn_debug_send(
+        //     channel,
+        //     &cxp_proto::UpConnPacket::Event {
+        //         conn_id: 0x1234_5678_u32,
+        //         packet_tag: 0x69_u8,
+        //         length: data_size + 3,
+        //         event_size: data_size,
+        //         namespace: 0x02_u8,
+        //         event_id: 0x00_6969u16,
+        //         timestamp: 0x1234_5678u64,
+        //         data: data_slice,
+        //     },
+        // )
+        // .expect("loopback gtx tx error");
+
+        // timer.delay_us(1000); // wait packet has arrive at RX async fifo
+
+        // if (CXP[channel].downconn_trigger_ack_read)() == 1 {
+        //     (CXP[channel].downconn_trigger_ack_write)(1);
+        //     info!("trig ack and cleared");
+        // }
+
+        // if (CXP[channel].downconn_bootstrap_decoder_err_read)() == 1 {
+        //     info!("!!!!!!!DECODER ERROR!!!!!!! and cleared");
+        //     (CXP[channel].downconn_bootstrap_decoder_err_write)(1);
+        // }
+
+        // info!("packet type = {:#06X}", (CXP[channel].downconn_packet_type_read)());
+
+        // // cxp_proto::receive(channel as u8).expect("loopback gtx rx error");
+        // // cxp_proto::downconn_debug_mem_print(channel);
+
+        // // DEBUG: print loopback packets
+        // const LEN: usize = 20;
+        // let mut pak_arr: [u32; LEN] = [0; LEN];
+        // let mut k_arr: [u8; LEN] = [0; LEN];
+        // let mut i: usize = 0;
+        // while (CXP[channel].downconn_debug_out_dout_valid_read)() == 1 {
+        //     pak_arr[i] = (CXP[channel].downconn_debug_out_dout_pak_read)();
+        //     k_arr[i] = (CXP[channel].downconn_debug_out_kout_pak_read)();
+        //     // println!("received {:#04X}", pak_arr[i]);
+        //     (CXP[channel].downconn_debug_out_inc_write)(1);
+        //     i += 1;
+        //     if i == LEN {
+        //         break;
+        //     }
+        // }
+
+        // info!("rx ready = {}", (CXP[channel].downconn_rx_ready_read)());
+        // // cxp_proto::print_packetu32(&pak_arr, &k_arr);
+    }
+}