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目录

引言

知识储备

时钟创建

时钟偏差 

 时钟延迟

 转换时间

 输入路径约束

 输出路径延迟

 组合逻辑路径约束

时间预算

 寄存器输出

总结

实际操作

设计文件

check_design

reset_design

时序约束

check_timing

compile

report_constraint -all_violators

remove_design -hierarchy

TCL脚本文件

dcprocheck

source ../script/MY_TOP.tcl

查看时序报告

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引言

本篇继续学习 DC的基本使用。本篇主要学习 DC 需要的时序约束。

前文链接：

Design Compiler工具学习笔记（1）

Design Compiler工具学习笔记（2）

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知识储备

时钟创建

时钟偏差 

 时钟延迟

 转换时间

 输入路径约束

 输出路径延迟

 组合逻辑路径约束

 指定输入延迟、输出延迟，以及时钟周期，可以得到中间组合逻辑 F 的延迟不超过

时钟周期-输入延迟-输出延迟

 纯组合逻辑，需要创建虚拟时钟，

​

​

时间预算

 寄存器输出

总结

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实际操作

写了一个很简单的设计文件：

设计文件

顶层：

// ================== TOP module =======================================
// Date:2022-11-20
// By:Xu Y. B.
// Description:
// use I_CNT_CTRL_A signal's posedge to control the counter in the time 
// domain B to count .
// =====================================================================

module TOP (
// time domain A 100MHz
input 			I_CNT_CTRL_A,    // input signal that needs to be synchronized
// time domain B 50MHz
input 			I_CLK_B,		 // clock B 50MHz
input 			I_RSTN_B,		 // synchronous reset active low
// output 
output reg [3:0]O_SYNC_DATA_B    // output counter 
	
);

// internal signals
wire W_SYNC_CTRL_B;				// I_CNT_CTRL_A synchronize to time domain B
reg  R_W_SYNC_CTRL_B_R1;		// W_SYNC_CTRL_B register one clock
wire W_SYNC_CTRL_B_PDG;			// posedge of W_SYNC_CTRL_B

// module logic
always @ (posedge I_CLK_B)
begin:register
	if(~I_RSTN_B)
	begin
		R_W_SYNC_CTRL_B_R1 <= 0;
	end
	else
	begin
		R_W_SYNC_CTRL_B_R1 <= W_SYNC_CTRL_B;
	end
end

assign W_SYNC_CTRL_B_PDG = W_SYNC_CTRL_B & (~R_W_SYNC_CTRL_B_R1);

// count
always @ (posedge I_CLK_B)
begin:count_B
	if(~I_RSTN_B)
	begin
		O_SYNC_DATA_B <= 4'd0;
	end
	else
	begin
		if(W_SYNC_CTRL_B_PDG)
		begin
			O_SYNC_DATA_B <= 3'd0;
		end
		else if(&O_SYNC_DATA_B)
		begin
			O_SYNC_DATA_B <= O_SYNC_DATA_B;
		end
		else
		begin
			O_SYNC_DATA_B <= O_SYNC_DATA_B + 1;
		end
	end
end


// module instantiate
sync_2 INST_sync_2 (.I_CLK(I_CLK_B), .I_RSTN(I_RSTN_B), .I_DATA(I_CNT_CTRL_A), .O_SYNC_DATA(W_SYNC_CTRL_B));

endmodule

sync_2：

// ================== single-bit signal two stages synchronizer =================
// Date:2022-11-20
// By:Xu Y. B.
// ==============================================================================

module sync_2 (
	input I_CLK,    	// clock
	input I_RSTN,   	// synchronous reset active low
	input I_DATA,   	// input signal that needs to be synchronized

	output O_SYNC_DATA  // output signal that has been synchronized
	
);

reg [1:0]	R_SYNC;

always @ (posedge I_CLK)
begin:sync
	if(~I_RSTN)
	begin
		R_SYNC <= 2'b00;
	end
	else
	begin
		R_SYNC[0] <= I_DATA;
		R_SYNC[1] <= R_SYNC[0];
	end
end
assign O_SYNC_DATA = R_SYNC[1];

endmodule

首先按照上篇文章的流程读取设计文件，并且做库的链接。

然后进行后续操作：

check_design

 返回 1 表示正确可用。

reset_design

 返回 1 ，表示正确操作。目的是将涉及置于初始状态，去除一切约束。

时序约束

此处的约束种类比较多，后面会在 tcl 脚本里面详细阐述。

check_timing

主要用来检查时序约束的完整性。

compile

此步骤完成设计的编译即网表映射。

report_constraint -all_violators

查看时序违规

remove_design -hierarchy

将设计全部移除。

TCL脚本文件

# |===========================================================
# | Author 		: Xu Y. B.
# | Date   		: 2022-11-21
# | Description : tcl script for top design 
# |===========================================================


# |===========================================================
# |STEP 1: Read & elaborate the RTL design file list & check
# |===========================================================
set TOP_MODULE TOP
analyze        -format verilog [list TOP.v sync_2.v]
elaborate      $TOP_MODULE     -architecture verilog
current_design $TOP_MODULE

if {[link] == 0} {
	echo "Your Link has errors !";
	exit;
}

if {[check_design] == 0} {
	echo "Your check design has errors !";
	exit;
}

# |===========================================================
# |STEP 2: reset design
# |===========================================================
reset_design


# |===========================================================
# |STEP 3: Write unmapped ddc file
# |===========================================================
uniquify
set uniquify_naming_style "%s_%d"
write -f ddc -hierarchy -output ${UNMAPPED_PATH}/${TOP_MODULE}.ddc


# |===========================================================
# |STEP 4: define clocks
# |===========================================================
set       CLK_NAME          	I_CLK_B
set       CLK_PERIOD        	20
set       CLK_SKEW	        	[expr {$CLK_PERIOD*0.05}]						
set       CLK_TRANS         	[expr {$CLK_PERIOD*0.01}]						
set       CLK_SRC_LATENCY   	[expr {$CLK_PERIOD*0.1 }]						
set       CLK_LATENCY       	[expr {$CLK_PERIOD*0.1 }]						

create_clock 			-period 	$CLK_PERIOD  	  [get_ports $CLK_NAME]
set_ideal_network 						 			  [get_ports $CLK_NAME]
set_dont_touch_network 					 			  [get_ports $CLK_NAME]
set_drive 				0 							  [get_ports $CLK_NAME]

set_clock_uncertainty   -setup       $CLK_SKEW        [get_clocks $CLK_NAME]
set_clock_transition    -max         $CLK_TRANS       [get_clocks $CLK_NAME]
set_clock_latency       -source -max $CLK_SRC_LATENCY [get_clocks $CLK_NAME]
set_clock_latency       -max         $CLK_LATENCY     [get_clocks $CLK_NAME]


# |===========================================================
# |STEP 5: define reset
# |===========================================================
set RST_NAME 					I_RSTN_B
set_ideal_network 				[get_ports $RST_NAME]
set_dont_touch_network          [get_ports $RST_NAME]
set_drive             0         [get_ports $RST_NAME]


# |===========================================================
# |STEP 6: set input delay using timing budget
# |Assume a weak cell to drive the input pins
# |===========================================================
set 		LIB_NAME 			typical
set 		WIRE_LOAD_MODULE 	smic18_wl10
set 		DRIVE_CELL 			INVX1
set 		DRIVE_PIN 			Y
set 		OPERATE_CONDITION   typical

set 		ALL_INPUT_EXCEPT_CLK [remove_from_collection [all_inputs] [get_ports "$CLK_NAME"]]
set         INPUT_DELAY 		 [expr {$CLK_PERIOD*0.6}]

set_input_delay $INPUT_DELAY -clock $CLK_NAME $ALL_INPUT_EXCEPT_CLK
# set_input_delay -min 0 -clock $CLK_NAME $ALL_INPUT_EXCEPT_CLK
set_driving_cell -lib_cell ${DRIVE_CELL} -pin ${DRIVE_PIN} $ALL_INPUT_EXCEPT_CLK


# |===========================================================
# |STEP 7: set output delay 
# |===========================================================
set output_DELAY  [expr {$CLK_PERIOD*0.6}]
set MAX_LOAD      [expr {[load_of $LIB_NAME/INVX8/A] * 10}]

set_output_delay  $output_DELAY -clock $CLK_NAME 	 [all_outputs]
set_load 		  [expr {$MAX_LOAD * 3}] 			 [all_outputs]
set_isolate_ports -type buffer 					 	 [all_outputs]


# |===========================================================
# |STEP 8: set max delay for comb logic 
# |===========================================================
# set_input_delay  [expr $CLK_PERIOD * 0.1] -clock $CLK_NAME -add_delay [get_ports I_1]
# set_output_delay [expr $CLK_PERIOD * 0.1] -clock $CLK_NAME -add_delay [get_ports O_1]


# |===========================================================
# |STEP 9: set operating condition & wire load model 
# |===========================================================
set_operating_conditions -max 			$OPERATE_CONDITION \
						 -max_library 	$LIB_NAME

set auto_wire_load_selection false

dcprocheck

检查 tcl 脚本有无语法问题。

故意打错一个命令：

​

 出现了未定义程序的警告需要重视。

source ../script/MY_TOP.tcl

执行脚本，注意路径。

查看时序报告