以太网控制器计数器模块实现代码

计数器模块提供数据发送过程中需要的所有计数器：DlyCrcCnt 用来在 CRC 校验序列产生过程中计数；按照 4 位传输时采用 NibCnt 计数；按照字节传输时采用 ByteCnt 计数。计数器模块的主要代码如下：

//四位传输计数器
always @ (posedge MTxClk or posedge Reset)
begin
if(Reset)
NibCnt <= #Tp 16'h0;
else
begin
if(ResetNibCnt)
NibCnt <= #Tp 16'h0;
else
if(IncrementNibCnt)
NibCnt <= #Tp NibCnt + 1'b1;
end
end
assign NibCntEq7 = &NibCnt[2:0];
assign NibCntEq15 = &NibCnt[3:0];
assign NibbleMinFl = NibCnt >= (((MinFL-3'h4)<<1) -1); // FCS should not be included inNibbleMinFl
assign ExcessiveDeferCnt = NibCnt[13:0] == 16'h17b7;
assign ExcessiveDefer = NibCnt[13:0] == 16'h17b7 & ~ExDfrEn; // 6071 nibbles
assign IncrementByteCnt = StateData[1] & ~ByteCntMax & ~|DlyCrcCnt[2:0]
| StateBackOff & (&NibCnt[6:0])
| (StatePAD | StateFCS) & NibCnt[0] & ~ByteCntMax;
assign ResetByteCnt = StartBackoff | StateIdle & TxStartFrm | PacketFinished_q;
// 字节传输计数器
always @ (posedge MTxClk or posedge Reset)
begin
if(Reset)
ByteCnt[15:0] <= #Tp 16'h0;
else
begin
if(ResetByteCnt)
ByteCnt[15:0] <= #Tp 16'h0;
else
if(IncrementByteCnt)
ByteCnt[15:0] <= #Tp ByteCnt[15:0] + 1'b1;
end
end
assign MaxFrame = ByteCnt[15:0] == MaxFL[15:0] & ~HugEn;
assign ByteCntMax = &ByteCnt[15:0];
//CRC 计数器
always @ (posedge MTxClk or posedge Reset)
begin
if(Reset)
DlyCrcCnt <= #Tp 3'h0;
else
begin
if(StateData[1] & DlyCrcCnt == 3'h4 | StartJam | PacketFinished_q)
DlyCrcCnt <= #Tp 3'h0;
else
if(DlyCrcEn & (StateSFD | StateData[1] & (|DlyCrcCnt[2:0])))
DlyCrcCnt <= #Tp DlyCrcCnt + 1'b1;
end
end

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