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Rework PHC to register shared adder outputs for improved timing performance

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Signed-off-by: Alex Forencich <alex@alexforencich.com>
This commit is contained in:
Alex Forencich 2023-12-02 00:53:02 -08:00
parent dd97924714
commit dce0c92a57
1 changed files with 245 additions and 209 deletions
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454
rtl/ptp_td_phc.v
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@ -154,10 +154,9 @@ reg [3:0] update_state_reg = 0;
reg [47:0] adder_a_reg = 0;
reg [47:0] adder_b_reg = 0;
reg adder_cin_reg = 0;
wire [47:0] adder_sum;
wire adder_cout;
assign {adder_cout, adder_sum} = adder_a_reg + adder_b_reg + adder_cin_reg;
reg [47:0] adder_sum_reg = 0;
reg adder_cout_reg = 0;
reg adder_busy_reg = 0;
assign input_ts_tod_ready = input_ts_tod_ready_reg;
assign input_ts_tod_offset_ready = input_ts_tod_offset_ready_reg;
@ -225,8 +224,7 @@ always @(posedge clk) begin
pps_gen_ns_reg <= pps_gen_ns_reg + pps_gen_ns_inc_reg;
if (!pps_gen_ns_reg[30]) begin
// pps_delay_reg <= 14*17 + 32 + 1;
pps_delay_reg <= 14*17 + 32 + 248;
pps_delay_reg <= 14*17 + 32 + 240;
pps_gen_ns_reg[30] <= 1'b1;
end
@ -245,231 +243,269 @@ always @(posedge clk) begin
end
// update state machine
case (update_state_reg)
0: begin
// idle
{adder_cout_reg, adder_sum_reg} <= adder_a_reg + adder_b_reg + adder_cin_reg;
adder_busy_reg <= 1'b0;
// set relative timestamp
if (input_ts_rel_valid) begin
ts_rel_ns_reg <= input_ts_rel_ns;
input_ts_rel_ready_reg <= 1'b1;
ts_rel_updated_reg <= 1'b1;
end
// computes the following:
// {ts_inc_ns_reg, ts_fns_reg} = drift_acc_reg + $signed(input_ts_offset_fns) + {period_ns_reg, period_fns_reg} * 256 + ts_fns_reg
// ts_rel_ns_reg = ts_rel_ns_reg + ts_inc_ns_reg + $signed(input_ts_rel_offset_ns);
// ts_tod_ns_reg = ts_tod_ns_reg + ts_inc_ns_reg + $signed(input_ts_tod_offset_ns);
// if that borrowed,
// ts_tod_ns_reg = ts_tod_ns_reg + NS_PER_S
// ts_tod_s_reg = ts_tod_s_reg - 1
// else
// pps_gen_ns_reg = ts_tod_ns_reg - NS_PER_S
// if that did not borrow,
// ts_tod_ns_reg = ts_tod_ns_reg - NS_PER_S
// ts_tod_s_reg = ts_tod_s_reg + 1
// ts_tod_offset_ns_reg = ts_tod_ns_reg - ts_rel_ns_reg
// if ts_tod_ns_reg[29]
// ts_tod_alt_offset_ns_reg = ts_tod_offset_ns_reg - NS_PER_S
// ts_tod_alt_s_reg = ts_tod_s_reg + 1
// else
// ts_tod_alt_offset_ns_reg = ts_tod_offset_ns_reg + NS_PER_S
// ts_tod_alt_s_reg = ts_tod_s_reg - 1
// set ToD timestamp
if (input_ts_tod_valid) begin
ts_tod_s_reg <= input_ts_tod_s;
ts_tod_ns_reg <= input_ts_tod_ns;
input_ts_tod_ready_reg <= 1'b1;
ts_tod_updated_reg <= 1'b1;
end
if (!adder_busy_reg) begin
case (update_state_reg)
0: begin
// idle
// compute period 1 - add drift and requested offset
if (drift_apply_reg) begin
adder_a_reg <= drift_acc_reg + drift_num_reg;
end else begin
adder_a_reg <= drift_acc_reg;
end
adder_b_reg <= input_ts_offset_valid ? $signed(input_ts_offset_fns) : 0;
adder_cin_reg <= 0;
// set relative timestamp
if (input_ts_rel_valid) begin
ts_rel_ns_reg <= input_ts_rel_ns;
input_ts_rel_ready_reg <= 1'b1;
ts_rel_updated_reg <= 1'b1;
end
if (td_update_reg) begin
drift_acc_reg <= 0;
input_ts_offset_ready_reg <= input_ts_offset_valid;
update_state_reg <= 1;
end else begin
update_state_reg <= 0;
end
end
1: begin
// compute period 2 - add drift and offset to period
adder_a_reg <= adder_sum;
adder_b_reg <= {period_ns_reg, period_fns_reg, 8'd0};
adder_cin_reg <= 0;
// set ToD timestamp
if (input_ts_tod_valid) begin
ts_tod_s_reg <= input_ts_tod_s;
ts_tod_ns_reg <= input_ts_tod_ns;
input_ts_tod_ready_reg <= 1'b1;
ts_tod_updated_reg <= 1'b1;
end
update_state_reg <= 2;
end
2: begin
// compute next fns
adder_a_reg <= adder_sum;
adder_b_reg <= ts_fns_reg;
adder_cin_reg <= 0;
update_state_reg <= 3;
end
3: begin
// store fns; compute relative timestamp 1 - add previous value and offset
{ts_inc_ns_reg, ts_fns_reg} <= {adder_cout, adder_sum};
adder_a_reg <= ts_rel_ns_reg;
adder_b_reg <= 0;
adder_cin_reg <= 0;
// offset relative timestamp if requested
if (input_ts_rel_offset_valid) begin
adder_b_reg <= $signed(input_ts_rel_offset_ns);
input_ts_rel_offset_ready_reg <= 1'b1;
ts_rel_updated_reg <= 1'b1;
end
update_state_reg <= 4;
end
4: begin
// compute relative timestamp 2 - add increment
adder_a_reg <= adder_sum;
adder_b_reg <= ts_inc_ns_reg;
adder_cin_reg <= 0;
update_state_reg <= 5;
end
5: begin
// store relative timestamp; compute ToD timestamp 1 - add previous value and increment
ts_rel_ns_reg <= adder_sum;
adder_a_reg <= ts_tod_ns_reg;
adder_b_reg <= ts_inc_ns_reg;
adder_cin_reg <= 0;
update_state_reg <= 6;
end
6: begin
// compute ToD timestamp 2 - add offset
adder_a_reg <= adder_sum;
adder_b_reg <= 0;
adder_cin_reg <= 0;
// offset ToD timestamp if requested
if (input_ts_tod_offset_valid) begin
adder_b_reg <= $signed(input_ts_tod_offset_ns);
input_ts_tod_offset_ready_reg <= 1'b1;
ts_tod_updated_reg <= 1'b1;
end
update_state_reg <= 7;
end
7: begin
// compute ToD timestamp 2 - check for underflow/overflow
ts_tod_ns_reg <= adder_sum;
if (adder_b_reg[47] && !adder_cout) begin
// borrowed; add 1 billion
adder_a_reg <= adder_sum;
adder_b_reg <= NS_PER_S;
// compute period 1 - add drift and requested offset
if (drift_apply_reg) begin
adder_a_reg <= drift_acc_reg + drift_num_reg;
end else begin
adder_a_reg <= drift_acc_reg;
end
adder_b_reg <= input_ts_offset_valid ? $signed(input_ts_offset_fns) : 0;
adder_cin_reg <= 0;
update_state_reg <= 8;
end else begin
// did not borrow; subtract 1 billion to check for overflow
adder_a_reg <= adder_sum;
if (td_update_reg) begin
drift_acc_reg <= 0;
input_ts_offset_ready_reg <= input_ts_offset_valid;
update_state_reg <= 1;
adder_busy_reg <= 1'b1;
end else begin
update_state_reg <= 0;
end
end
1: begin
// compute period 2 - add drift and offset to period
adder_a_reg <= adder_sum_reg;
adder_b_reg <= {period_ns_reg, period_fns_reg, 8'd0};
adder_cin_reg <= 0;
update_state_reg <= 2;
adder_busy_reg <= 1'b1;
end
2: begin
// compute next fns
adder_a_reg <= adder_sum_reg;
adder_b_reg <= ts_fns_reg;
adder_cin_reg <= 0;
update_state_reg <= 3;
adder_busy_reg <= 1'b1;
end
3: begin
// store fns
{ts_inc_ns_reg, ts_fns_reg} <= {adder_cout_reg, adder_sum_reg};
// compute relative timestamp 1 - add previous value and increment
adder_a_reg <= ts_rel_ns_reg;
adder_b_reg <= {adder_cout_reg, adder_sum_reg} >> FNS_W; // ts_inc_ns_reg
adder_cin_reg <= 0;
update_state_reg <= 4;
adder_busy_reg <= 1'b1;
end
4: begin
// compute relative timestamp 2 - add offset
adder_a_reg <= adder_sum_reg;
adder_b_reg <= 0;
adder_cin_reg <= 0;
// offset relative timestamp if requested
if (input_ts_rel_offset_valid) begin
adder_b_reg <= $signed(input_ts_rel_offset_ns);
input_ts_rel_offset_ready_reg <= 1'b1;
ts_rel_updated_reg <= 1'b1;
end
update_state_reg <= 5;
adder_busy_reg <= 1'b1;
end
5: begin
// store relative timestamp
ts_rel_ns_reg <= adder_sum_reg;
// compute ToD timestamp 1 - add previous value and increment
adder_a_reg <= ts_tod_ns_reg;
adder_b_reg <= ts_inc_ns_reg;
adder_cin_reg <= 0;
update_state_reg <= 6;
adder_busy_reg <= 1'b1;
end
6: begin
// compute ToD timestamp 2 - add offset
adder_a_reg <= adder_sum_reg;
adder_b_reg <= 0;
adder_cin_reg <= 0;
// offset ToD timestamp if requested
if (input_ts_tod_offset_valid) begin
adder_b_reg <= $signed(input_ts_tod_offset_ns);
input_ts_tod_offset_ready_reg <= 1'b1;
ts_tod_updated_reg <= 1'b1;
end
update_state_reg <= 7;
adder_busy_reg <= 1'b1;
end
7: begin
// compute ToD timestamp 3 - check for underflow/overflow
ts_tod_ns_reg <= adder_sum_reg;
if (adder_b_reg[47] && !adder_cout_reg) begin
// borrowed; add 1 billion
adder_a_reg <= adder_sum_reg;
adder_b_reg <= NS_PER_S;
adder_cin_reg <= 0;
update_state_reg <= 8;
adder_busy_reg <= 1'b1;
end else begin
// did not borrow; subtract 1 billion to check for overflow
adder_a_reg <= adder_sum_reg;
adder_b_reg <= -NS_PER_S;
adder_cin_reg <= 0;
update_state_reg <= 9;
adder_busy_reg <= 1'b1;
end
end
8: begin
// seconds decrement
ts_tod_ns_reg <= adder_sum_reg;
pps_gen_ns_reg[30] <= 1'b1;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= -1;
adder_cin_reg <= 0;
update_state_reg <= 10;
adder_busy_reg <= 1'b1;
end
9: begin
// seconds increment
pps_gen_ns_reg <= adder_sum_reg;
if (!adder_cout_reg) begin
// borrowed; leave seconds alone
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= 0;
adder_cin_reg <= 0;
end else begin
// did not borrow; increment seconds
ts_tod_ns_reg <= adder_sum_reg;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= 1;
adder_cin_reg <= 0;
end
update_state_reg <= 10;
adder_busy_reg <= 1'b1;
end
10: begin
// store seconds
ts_tod_s_reg <= adder_sum_reg;
// compute offset
adder_a_reg <= ts_tod_ns_reg;
adder_b_reg <= ~ts_rel_ns_reg;
adder_cin_reg <= 1;
update_state_reg <= 11;
adder_busy_reg <= 1'b1;
end
11: begin
// store offset
ts_tod_offset_ns_reg <= adder_sum_reg;
adder_a_reg <= adder_sum_reg;
adder_b_reg <= -NS_PER_S;
adder_cin_reg <= 0;
update_state_reg <= 9;
if (ts_tod_ns_reg[29]) begin
// latter half of second; compute offset for next second
adder_b_reg <= -NS_PER_S;
update_state_reg <= 12;
adder_busy_reg <= 1'b1;
end else begin
// former half of second; compute offset for previous second
adder_b_reg <= NS_PER_S;
update_state_reg <= 14;
adder_busy_reg <= 1'b1;
end
end
end
8: begin
// seconds decrement
ts_tod_ns_reg <= adder_sum;
pps_gen_ns_reg[30] <= 1'b1;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= -1;
adder_cin_reg <= 0;
update_state_reg <= 10;
end
9: begin
// seconds increment
pps_gen_ns_reg <= adder_sum;
if (!adder_cout) begin
// borrowed; leave seconds alone
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= 0;
adder_cin_reg <= 0;
end else begin
// did not borrow; decrement seconds
ts_tod_ns_reg <= adder_sum;
12: begin
// store alternate offset for next second
ts_tod_alt_offset_ns_reg <= adder_sum_reg;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= 1;
adder_cin_reg <= 0;
update_state_reg <= 13;
adder_busy_reg <= 1'b1;
end
13: begin
// store alternate second for next second
ts_tod_alt_s_reg <= adder_sum_reg;
update_state_reg <= 10;
end
10: begin
// store seconds; compute offset
ts_tod_s_reg <= adder_sum;
if (adder_sum == ts_tod_alt_s_reg) begin
// store previous offset as alternate
ts_tod_alt_s_reg <= ts_tod_s_reg;
ts_tod_alt_offset_ns_reg <= ts_tod_offset_ns_reg;
update_state_reg <= 0;
end
14: begin
// store alternate offset for previous second
ts_tod_alt_offset_ns_reg <= adder_sum_reg;
adder_a_reg <= ts_tod_ns_reg;
adder_b_reg <= ~ts_rel_ns_reg;
adder_cin_reg <= 1;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= -1;
adder_cin_reg <= 0;
update_state_reg <= 11;
end
11: begin
// store offset
ts_tod_offset_ns_reg <= adder_sum;
adder_a_reg <= adder_sum;
adder_b_reg <= -NS_PER_S;
adder_cin_reg <= 0;
if (ts_tod_ns_reg[29]) begin
// latter half of second; compute offset for next second
adder_b_reg <= -NS_PER_S;
update_state_reg <= 12;
end else begin
// former half of second; compute offset for previous second
adder_b_reg <= NS_PER_S;
update_state_reg <= 14;
update_state_reg <= 15;
adder_busy_reg <= 1'b1;
end
end
12: begin
// store alternate offset for next second
ts_tod_alt_offset_ns_reg <= adder_sum;
15: begin
// store alternate second for previous second
ts_tod_alt_s_reg <= adder_sum_reg;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= 1;
adder_cin_reg <= 0;
update_state_reg <= 13;
end
13: begin
// store alternate second for next second
ts_tod_alt_s_reg <= adder_sum;
update_state_reg <= 0;
end
14: begin
// store alternate offset for previous second
ts_tod_alt_offset_ns_reg <= adder_sum;
adder_a_reg <= ts_tod_s_reg;
adder_b_reg <= -1;
adder_cin_reg <= 0;
update_state_reg <= 15;
end
15: begin
// store alternate second for previous second
ts_tod_alt_s_reg <= adder_sum;
update_state_reg <= 0;
end
default: begin
// invalid state; return to idle
update_state_reg <= 0;
end
endcase
update_state_reg <= 0;
end
default: begin
// invalid state; return to idle
update_state_reg <= 0;
end
endcase
end
// time distribution message generation
td_shift_reg <= {1'b1, td_shift_reg} >> 1;