The Loopback Master feature is implemented in the VSEC space. Loopback Master
capability for Root Port starts at byte address 'h330.
To exercise Loopback Start, use the cfg_mgmt interface
to write 1'b1 to bit 0 in byte address 'h338 (Loopback Control).
Because
cfg_mgmt uses DW addresses, use
cfg_mgmt_write_data = 32'h1 to address: -
cfg_mgmt_address=10'hCE -
cfg_mgmt_write=1'b1 -
cfg_mgmt_byte_enable=4'b1
After Start Loopback, retrain the link by writing to the link control
register (byte address:
'h80, DW address: 'h20). Use cfg_mgmt_write_data = 'h20 to address:-
cfg_mgmt_address=10'h20 -
cfg_mgmt_write=1'b1 -
cfg_mgmt_byte_enable=4'b1