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7df9186 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | // 16-bit ones-complement checksum calculator
// Applies to all of IP header, ICMP, and UDP checksums
// Well, difficult to use with UDP because of its pathological
// inclusion of _two_ copies of the UDP length.
// mostly cribbed from core/assemble_eth.v
module ones_chksum(
input clk,
input clear,
input gate,
input [7:0] din,
output [7:0] sum,
output all_ones
);
reg [7:0] chksum=0, chksum1=0;
reg chksum_carry=0;
always @(posedge clk) begin
if (clear) {chksum_carry, chksum} <= 9'h0;
else if (gate) {chksum_carry, chksum} <=
chksum1 + din + chksum_carry;
if (clear) chksum1 <= 8'h0;
else if (gate) chksum1 <= chksum;
end
assign sum = ~(chksum1 + chksum_carry);
assign all_ones = &chksum;
endmodule
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