Achronix Speedster22i SerDes - Manual (Page 75)

Dynamically Changing the SerDes Register Values
Typically the PMA/PCS registers need not be changed during runtime. However,
simple_serdes_design uses internal SerDes loopback. Internal loopback may be the starting
point for the users to verify the functionality of any user-design. To enable the internal
loopback, the user needs to dynamically ( at run-time) set a PCS register via the SBUS
interface. This is done using the ACX_SERDES_LOOPBACK_CTRL module explained in
Chapter – “Dynamic Read/Write of SerDes Registers (Through SBUS)”. Internal loopback
cannot be programmed statically (in the ACE-generated bitstream). Section Loopback
Modes presents the loopback modes available with Achronix SerDes. The code below shows
an example of using ACX_SERDES_LOOPBACK_CTRL (reproduced from Chapter –
“Dynamic Read/Write of SerDes Registers (Through SBUS)” for ready reference).
Using sBus module to enable internal loopback
The code below shows how to enable internal loopback using the sBus
wire sbus_ln0_done;
wire inv_sbus_disable_loopback_ln0;
assign inv_sbus_disable_loopback_ln0 = ~i_sbus_disable_loopback;
wire unused_ln0_i_reg_write;
wire unused_ln0_i_reg_rw_req;
wire unused_ln0_i_reg_pma;
wire unused_ln0_i_reg_address;
wire unused_ln0_i_reg_wr_data;
wire unused_ln0_o_reg_rd_data;
wire unused_ln0_o_reg_rdwr_valid;
ACX_SERDES_LOOPBACK_CTRL #(
.LOOPBACK_MODE (`LPBK_TX_RX_PMA_INTERNAL),
.ENABLE_PASS_THROUGH(0)
)
i_loopback_ctl_ln0
(
.sbus_clk (i_sclk),
.rstn (1'b1), // ok to tie high
.disable_loopback (inv_sbus_disable_loopback_ln6), // rising edge disables loopback
.done (sbus_ln0_done), // program is finished
// serdes connections
.from_sbus_data (ln0_sbus_rddata[1:0]),
.from_sbus_ack (ln0_sbus_ack),
.to_sbus_data (ln0_sbus_wrdata[1:0]),
.to_sbus_req (ln0_sbus_req),
.i_pma_synthready (ln0_synthready),
.i_pma_TXready (ln0_TX_ready),
.i_pma_RXready (ln0_RX_ready),
.to_sbus_sw_rst (ln0_sbus_sw_rst),
// pass-through connections, can be used when 'done' is high
// (ignored if ENABLE_PASS_THROUGH = 0)
.i_reg_write (unused_ln0_i_reg_write), // request is ‘write'
.i_reg_rw_req (unused_ln0_i_reg_rw_req), // rising edge starts action
.i_reg_pma (unused_ln0_i_reg_pma), // address is pma address
.i_reg_address (unused_ln0_i_reg_address), // 16-bit pcs or pma address
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