FPGA分频与倍频的简单总结（涉及自己设计，调用时钟IP核，调用MMCM原语模块）

原理介绍

1、分频

FPGA设计中时钟分频是重要的基础知识，对于分频通常是利用计数器来实现想要的时钟频率，由此可知分频后的频率周期更大。一般而言实现偶数系数的分频在程序设计上较为容易，而奇数分频则相对复杂一些，小数分频则更难一些。

1）偶分频系数=时钟输入频率/时钟输出频率=50MHz/5MHz=10，则计数器在输入时钟的上升沿或者下降沿从0~（10-1）计数，而输出时钟在计数到4和9时翻转。

2）奇分频系数=50MHz/10MHz=5，则两个计数器分别在输入时钟的上升沿和下降沿从0~ （5-1）计数，而相应的上升沿和下降沿触发的输出时钟在计数到1和4时翻转，最后将两个输出时钟进行或运算从而得到占空比为50%的5分频输出时钟。

下图所示为50MHz输入时钟进行10分频和5分频的仿真波形

 

2、倍频

两种思路：PLL（锁相环）或者利用门延时来搭建

 

注意：此仿真是利用FPGA内部电路延迟来实现的倍频需要在后仿真下才能看到波形，在行为仿真下无法得到输出波形。

 

一、时钟IP的分频倍频相关参数说明

输入时钟：clk_in1(125MHz)

输出时钟：clk_out1(50MHz)，clk_out2(74.25MHz)

则VCO Freq=1262.5MHz=clk_in1*CLKFBOUT_MULT_F/DIVCLK_DIVIDE=125*50.5/5

clk_out1(50MHz)=VCO_Freq/Divide=1265.5/25.250

clk_out2(74.25MHz)=VCO_Freq/Divide=1265.5/17

 

二、MMCME4_ADV

MMCME4是一种混合信号块，用于支持频率合成、时钟网络设计和减少抖动。基于相同的VCO频率，时钟输出可以有单独的分频、相移和占空比。此外，MMCME4还支持动态移相和分数除法

 

（1）Verilog 初始化模板

MMCME4_ADV #(
.BANDWIDTH("OPTIMIZED"), // Jitter programming
.CLKFBOUT_MULT_F(5.0), // Multiply value for all CLKOUT
.CLKFBOUT_PHASE(0.0), // Phase offset in degrees of CLKFB
.CLKFBOUT_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKIN1_PERIOD(0.0), // Input clock period in ns to ps resolution (i.e. 33.333 is 30 MHz).
.CLKIN2_PERIOD(0.0), // Input clock period in ns to ps resolution (i.e. 33.333 is 30 MHz).
.CLKOUT0_DIVIDE_F(1.0), // Divide amount for CLKOUT0
.CLKOUT0_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT0
.CLKOUT0_PHASE(0.0), // Phase offset for CLKOUT0
.CLKOUT0_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT1_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT1_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT1_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT1_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT2_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT2_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT2_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT2_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT3_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT3_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT3_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT3_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT4_CASCADE("FALSE"), // Divide amount for CLKOUT (1-128)
.CLKOUT4_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT4_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT4_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT4_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT5_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT5_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT5_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT5_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.CLKOUT6_DIVIDE(1), // Divide amount for CLKOUT (1-128)
.CLKOUT6_DUTY_CYCLE(0.5), // Duty cycle for CLKOUT outputs (0.001-0.999).
.CLKOUT6_PHASE(0.0), // Phase offset for CLKOUT outputs (-360.000-360.000).
.CLKOUT6_USE_FINE_PS("FALSE"), // Fine phase shift enable (TRUE/FALSE)
.COMPENSATION("AUTO"), // Clock input compensation
.DIVCLK_DIVIDE(1), // Master division value
.IS_CLKFBIN_INVERTED(1'b0), // Optional inversion for CLKFBIN
.IS_CLKIN1_INVERTED(1'b0), // Optional inversion for CLKIN1
.IS_CLKIN2_INVERTED(1'b0), // Optional inversion for CLKIN2
.IS_CLKINSEL_INVERTED(1'b0), // Optional inversion for CLKINSEL
.IS_PSEN_INVERTED(1'b0), // Optional inversion for PSEN
.IS_PSINCDEC_INVERTED(1'b0), // Optional inversion for PSINCDEC
.IS_PWRDWN_INVERTED(1'b0), // Optional inversion for PWRDWN
.IS_RST_INVERTED(1'b0), // Optional inversion for RST
.REF_JITTER1(0.0), // Reference input jitter in UI (0.000-0.999).
.REF_JITTER2(0.0), // Reference input jitter in UI (0.000-0.999).
.SS_EN("FALSE"), // Enables spread spectrum
.SS_MODE("CENTER_HIGH"), // Spread spectrum frequency deviation and the spread type
.SS_MOD_PERIOD(10000), // Spread spectrum modulation period (ns)
.STARTUP_WAIT("FALSE") // Delays DONE until MMCM is locked
)
MMCME4_ADV_inst (
.CDDCDONE(CDDCDONE), // 1-bit output: Clock dynamic divide done
.CLKFBOUT(CLKFBOUT), // 1-bit output: Feedback clock
.CLKFBOUTB(CLKFBOUTB), // 1-bit output: Inverted CLKFBOUT
.CLKFBSTOPPED(CLKFBSTOPPED), // 1-bit output: Feedback clock stopped
.CLKINSTOPPED(CLKINSTOPPED), // 1-bit output: Input clock stopped
.CLKOUT0(CLKOUT0), // 1-bit output: CLKOUT0
.CLKOUT0B(CLKOUT0B), // 1-bit output: Inverted CLKOUT0
.CLKOUT1(CLKOUT1), // 1-bit output: CLKOUT1
.CLKOUT1B(CLKOUT1B), // 1-bit output: Inverted CLKOUT1

.CLKOUT2(CLKOUT2), // 1-bit output: CLKOUT2
.CLKOUT2B(CLKOUT2B), // 1-bit output: Inverted CLKOUT2
.CLKOUT3(CLKOUT3), // 1-bit output: CLKOUT3
.CLKOUT3B(CLKOUT3B), // 1-bit output: Inverted CLKOUT3
.CLKOUT4(CLKOUT4), // 1-bit output: CLKOUT4
.CLKOUT5(CLKOUT5), // 1-bit output: CLKOUT5
.CLKOUT6(CLKOUT6), // 1-bit output: CLKOUT6
.DO(DO), // 16-bit output: DRP data output
.DRDY(DRDY), // 1-bit output: DRP ready
.LOCKED(LOCKED), // 1-bit output: LOCK
.PSDONE(PSDONE), // 1-bit output: Phase shift done
.CDDCREQ(CDDCREQ), // 1-bit input: Request to dynamic divide clock
.CLKFBIN(CLKFBIN), // 1-bit input: Feedback clock
.CLKIN1(CLKIN1), // 1-bit input: Primary clock
.CLKIN2(CLKIN2), // 1-bit input: Secondary clock
.CLKINSEL(CLKINSEL), // 1-bit input: Clock select, High=CLKIN1 Low=CLKIN2
.DADDR(DADDR), // 7-bit input: DRP address
.DCLK(DCLK), // 1-bit input: DRP clock
.DEN(DEN), // 1-bit input: DRP enable
.DI(DI), // 16-bit input: DRP data input
.DWE(DWE), // 1-bit input: DRP write enable
.PSCLK(PSCLK), // 1-bit input: Phase shift clock
.PSEN(PSEN), // 1-bit input: Phase shift enable
.PSINCDEC(PSINCDEC), // 1-bit input: Phase shift increment/decrement
.PWRDWN(PWRDWN), // 1-bit input: Power-down
.RST(RST) // 1-bit input: Reset
);

（2）本实验仿真所用参数配置说明及部分端口调用

1、参数配置说明

本实验通过输入时钟CLKIN1(150MHz)，实现输出反馈时钟CLKFBOUT(150MHz)、输出时钟CLKOUT0(74.25MHz)、输出时钟CLKOUT1(74.25MHz)、输出时钟CLKOUT2(59.4MHz)、输出时钟CLKOUT3(49.5MHz)。其关键参数设置如下

CLKFBOUT_MULT_F（1.98）  //指定如果需要不同的频率，则对相关的CLKOUT时钟输出进行分数分割的乘法系数。这个数字与CLKFBOUT_MULT_F和DIVCLK_DIVIDE值的组合将决定输出频率

DIVCLK_DIVIDE（1）     //  指定所有输出时钟相对于输入时钟的除法因子       

CLKOUT0_DIVIDE_F(4)、 CLKOUT1_DIVIDE(4)、CLKOUT2_DIVIDE(5)、CLKOUT3_DIVIDE(6)   //指定分频输出的除法因子从而输出不同的频率

注：输入150MHz 乘以倍频因子1.98，得到倍频频率297MHz  ，由于DIVCLK_DIVIDE（1）设置为1，则分频的参考时钟为297/1=297；输出反馈时钟也为：297/1=297；那么其它CLKOUT_DIVIDE_F、CLKOUT1_DIVIDE~CLKOUT6_DIVIDE的分频根据设置的分频系数结合分频参考时钟297MHz而定，即参考分频时钟/相应分频系数，比如这里的297/4；297/5；297/6。其仿真波形如下图1所示

 

                                  图1

图2所示的波形仿真是改变了此参数设置：DIVCLK_DIVIDE(2)

 

                                                            图2

2、端口调用

MMCME4_ADV #(

.BANDWIDTH("OPTIMIZED"), // Jitter programming (HIGH, LOW, OPTIMIZED)

.CLKFBOUT_MULT_F(1.98), //

.CLKFBOUT_PHASE(0.0), //

.CLKIN1_PERIOD(6.6),

.CLKOUT0_DIVIDE_F(4), //

.CLKOUT1_DIVIDE(4),

.CLKOUT2_DIVIDE(5),

.CLKOUT3_DIVIDE(6),

.CLKOUT0_DUTY_CYCLE(0.5),

.CLKOUT1_DUTY_CYCLE(0.5),

.CLKOUT2_DUTY_CYCLE(0.5),

.CLKOUT3_DUTY_CYCLE(0.5),

.CLKOUT0_PHASE(0.0),

.CLKOUT1_PHASE(0.0),

.CLKOUT2_PHASE(0.0),

.CLKOUT3_PHASE(0.0),

 

.DIVCLK_DIVIDE(2), // Master division value (1-106)

.REF_JITTER1        (0.100)

)

MMCME4_ADV_inst (

// Clock Outputs outputs: User configurable clock outputs

.CLKOUT0(i_byte_clk), // 1-bit output: CLKOUT0

.CLKOUT0B(), // 1-bit output: Inverted CLKOUT0

.CLKOUT1(i_pix_clk74m25), // 1-bit output:

.CLKOUT1B(), // 1-bit output: Inverted CLKOUT1

.CLKOUT2(i_pix_clk59m4), // 1-bit output: CLKOUT2

.CLKOUT2B(), // 1-bit output: Inverted CLKOUT2

.CLKOUT3(i_pix_clk49m5), // 1-bit output: CLKOUT3

.CLKOUT3B(), // 1-bit output: Inverted CLKOUT3

 

// Feedback outputs: Clock feedback ports

.CLKFBOUT(mmcm_ser_ref_clk), // 1-bit output: Feedback clock

.CLKFBOUTB(), // 1-bit output: Inverted CLKFBOUT

// Status Ports outputs: MMCM status ports

.LOCKED(cmt_locked), // 1-bit output: LOCK

// Clock Inputs inputs: Clock inputs

.CLKIN1(clk150_g), // 1-bit input: Primary clock

// Control Ports inputs: MMCM control ports

.PWRDWN(1'b0), // 1-bit input: Power-down

.RST(i_ref_clk_rst) // 1-bit input: Reset

);

 

附：UltraScale+的高级混合模式时钟管理的三种原语库

MMCME3_ADV

The MMCME3 is a mixed signal block designed to support frequency synthesis, clock network
deskew, and jitter reduction. The clock outputs can each have an individual divide, phase shift
and duty cycle based on the same VCO frequency. Additionally, the MMCME3 supports dynamic
phase shifting and fractional divides.

 

MMCME3_BASE

The MMCME3 is a mixed signal block designed to support frequency synthesis, clock network
deskew, phase adjustment and jitter reduction. The MMCME3_BASE supports a subset of the
more common features and thus is easier to instantiate and use compared to the full features
MMCME3_ADV.

 

MMCME4_ADV

The MMCME4 is a mixed signal block designed to support frequency synthesis, clock network
deskew, and jitter reduction; The clock outputs can each have an individual divide, phase shif
and duty cycle based on the same VCO frequency. Additionally, the MMCME4 supports dynamic
phase shifting and fractional divides.