IIC传输协议及其代码的实现
01
IIC基础知识
集成电路总线（Inter-Intergrated Circuit)，通常称作IICBUS，简称为IIC，是一种采用多主从结构的串行通信总线。IIC由PHILIPS公司于1980年推出，利用该总线可实现多主机系统所需的裁决和高低速设备同步等功能。
IIC串行总线一般有两根信号线，分别是时钟线SCL和数据线SDA，所有IIC总线各设备的串行数据SDA接到总线SDA上，时钟线SLC接到总线SCL上。
双向串行数据SDA：输出电路用于向总线发送数据，输入电路用于接收总线上的数据；
双向时钟数据SCL：输出电路用于向总线发送时钟信号，输入电路用于检测总线时钟电平以决定下次时钟脉冲电平时间。
各设备与总线相连的输出端采用高阻态以避免总线信号的混乱，通常采用漏极开路输出或集电极开路输出。总线空闲时，各设备都是开漏输出，通常可采用上拉电阻使总线保持高电平，而任一设备输出低电平都将拉低相应的总线信号。
IIC总线上的设备可分为主设备和从设备两种：主设备有权利主动发起/结束一次通信；从设备只能被动响应。
所有连接在IIC总线上的设备都有各自唯一的地址(原地址位宽为7bits，改进后采用10bits位宽)，每个设备都可以作为主设备或从设备，但是同一时刻只能有一个主设备控制。
如果总线上有多个设备同时启用总线，IIC通过检测和仲裁机制解决传输冲突。IIC允许连接的设备传输速率不同，多台设备之间时钟信号的同步过程称为同步化。
02
IIC传输协议
2.1 IIC协议模式
IIC协议为半双工模式，同一条数据线上完成读/写操作，不同操作时的数据帧格式可分为写操作、读操作、读写操作。
2.1.1 写操作数据帧格式
主机向从机写数据的数据帧格式如下：
白色为主机发送数据，灰色为从机发送数据。
1. 主机发送开始信号S；
2. 主机发送地址数据ADDR；
3. 主机发送写信号0；
4. 从机响应主机写信号ACK；
5. 主机发送数据信息DATA；
6. 从机响应主机发送数据ACK；
7. 循环5 6步骤可完成主机向从机连续写数据过程；
8. 主机发送结束信号P.
2.1.2 读操作数据帧格式
主机从从机读数据的数据帧格式如下：
白色为主机发送数据，灰色为从机发送数据。
1. 主机发送开始信号S；
2. 主机发送地址数据ADDR；
3. 主机发送读信号1；
4. 从机响应主机读信号ACK；
5. 从机发送数据信息DATA；
6. 主机响应从机发送数据ACK；
7. 循环5 6步骤可完成主机向从机连续读数据过程；
8. 主机发送结束信号P.
2.1.3 读写同时操作数据帧格式
主机先向从机写数据后从从机读数据的数据帧格式如下：
白色为主机发送数据，灰色为从机发送数据。
主机可以在完成写操作后不发送结束信号P，直接进行读操作。该过程主机不可变，而从机可以通过发送不同地址选择不同的从机。
2.2 IIC写时序
IIC协议写时序可分为单字节写时序和连续写时序：
2.2.1 单字节写时序
单字节地址写时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送单字节寄存器地址信息WORD ADDRESS；
5. 从机响应主机发送寄存器地址ACK；
6. 主机发送单字节数据信息DATA；
7. 从机响应主机发送数据信息ACK；
8. 主机发送结束信号P.
双字节地址写时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送寄存器地址信息高字节ADDRESS HIGH BYTE；
5. 从机响应主机发送寄存器地址高字节ACK；
6. 主机发送寄存器地址信息低字节ADDRESS LOW BYTE；
7. 从机响应主机发送寄存器地址低字节ACK；
8. 主机发送单字节数据信息DATA；
9. 从机响应主机发送数据信息ACK；
10. 主机发送结束信号P.
2.2.2 连续写时序
单字节地址写时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送单字节寄存器地址信息WORD ADDRESS；
5. 从机响应主机发送寄存器地址ACK；
6. 主机发送单字节数据信息DATA；
7. 从机响应主机发送数据信息ACK；
8. 循环6 7步骤可以连续向从机写数据DATA(D+n)；
9. 主机发送结束信号P.
双字节地址写时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送寄存器地址信息高字节ADDRESS HIGH BYTE；
5. 从机响应主机发送寄存器地址高字节ACK；
6. 主机发送寄存器地址信息低字节ADDRESS LOW BYTE；
7. 从机响应主机发送寄存器地址低字节ACK；
8. 主机发送单字节数据信息DATA；
9. 从机响应主机发送数据信息ACK；
10. 循环8 9步骤可以连续向从机写数据DATA(D+n)；
11. 主机发送结束信号P.
2.3 IIC读时序
IIC协议读时序可分为单字节读时序和连续读时序：
2.3.1 单字节读时序
单字节地址读时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送单字节寄存器地址信息WORD ADDRESS；
5. 从机响应主机发送寄存器地址ACK；
6. 主机发送开始信号S；
7. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为1表示主机从从机读数据；
8. 从机响应主机控制字节ACK；
9. 从机发送单字节数据信息DATA；
10. 主机响应从机发送数据信息NACK(非应答位: 接收器是主机时，在接收到最后一个字节后发送NACK已通知被控发送从机结束数据发送，并释放SDA数据线以便主机发送停止信号P)；
11. 主机发送结束信号P.
双字节地址读时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送寄存器地址信息高字节ADDRESS HIGH BYTE；
5. 从机响应主机发送寄存器地址高字节ACK；
6. 主机发送寄存器地址信息低字节ADDRESS LOW BYTE；
7. 从机响应主机发送寄存器地址低字节ACK；
8. 主机发送开始信号S；
9. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为1表示主机从从机读数据；
10. 从机响应主机控制字节ACK；
11. 从机发送单字节数据信息DATA；
12. 主机响应从机发送数据信息NACK(非应答位: 接收器是主机时，在接收到最后一个字节后发送NACK已通知被控发送从机结束数据发送，并释放SDA数据线以便主机发送停止信号P)；
13. 主机发送结束信号P.
2.3.2 连续读时序
单字节地址读时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送单字节寄存器地址信息WORD ADDRESS；
5. 从机响应主机发送寄存器地址ACK；
6. 主机发送开始信号S；
7. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为1表示主机从从机读数据；
8. 从机响应主机控制字节ACK；
9. 从机发送单字节数据信息DATA；
10. 主机响应从机发送数据信息ACK；
11. 循环9 10步骤可完成主机向从机连续读数据过程，读取最后一个字节数据时主机应响应NACK(非应答位: 接收器是主机时，在接收到最后一个字节后发送NACK已通知被控发送从机结束数据发送，并释放SDA数据线以便主机发送停止信号P)；
12. 主机发送结束信号P.
双字节地址读时序过程：
1. 主机发送开始信号S；
2. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为0表示主机向从机写数据；
3. 从机响应主机控制字节ACK；
4. 主机发送寄存器地址信息高字节ADDRESS HIGH BYTE；
5. 从机响应主机发送寄存器地址高字节ACK；
6. 主机发送寄存器地址信息低字节ADDRESS LOW BYTE；
7. 从机响应主机发送寄存器地址低字节ACK；
8. 主机发送开始信号S；
9. 主机发送控制字节CONTROL BYTE(7bits设备地址dev addr和1bit读写信号)，最低位为1表示主机从从机读数据；
10. 从机响应主机控制字节ACK；
11. 从机发送单字节数据信息DATA；
12.主机响应从机发送数据信息ACK；
13. 循环11 12步骤可完成主机向从机连续读数据过程，读取最后一个字节数据时主机应响应NACK(非应答位: 接收器是主机时，在接收到最后一个字节后发送NACK已通知被控发送从机结束数据发送，并释放SDA数据线以便主机发送停止信号P)；
14. 主机发送结束信号P.
03
IIC代码实现
3.1 IIC目标实现功能
设计一个IIC模块，具体要求如下：
设计一个IIC协议提供给主设备，通过查找表实现对从设备寄存器进行配置。按查找表顺序lut_index依次对设备地址为lut_dev_addr的从设备寄存器进行配置，为lut_reg_addr配置寄存器数据lut_reg_data，同时将传输异常和传输结束信号引出以对传输过程进行监控。模块的定义如下：
module i2c(
input rst,//复位信号
input clk, //时钟信号
input[15:0] clk_div_cnt, //时钟计数器
input i2c_addr_2byte, //双字节地址
output reg[9:0] lut_index, //查找表顺序号
input[7:0] lut_dev_addr, //从设备地址
input[15:0] lut_reg_addr, //寄存器地址
input[7:0] lut_reg_data, //寄存器数据
output reg error, //传输异常信号
output done, //传输结束信号
inout i2c_scl, //IIC时钟信号
inout i2c_sda //IIC数据信号
);
3.2 Verilog代码
1. 顶层模块 (i2c)：
module i2c(
input rst,
input clk,
input[15:0] clk_div_cnt,
input i2c_addr_2byte,
output reg[9:0] lut_index,
input[7:0] lut_dev_addr,
input[15:0] lut_reg_addr,
input[7:0] lut_reg_data,
output reg error,
output done,
inout i2c_scl,
inout i2c_sda
);
wire scl_pad_i;
wire scl_pad_o;
wire scl_padoen_o;
wire sda_pad_i;
wire sda_pad_o;
wire sda_padoen_o;
assign sda_pad_i = i2c_sda;
assign i2c_sda = ~sda_padoen_o ? sda_pad_o : 1'bz;
assign scl_pad_i = i2c_scl;
assign i2c_scl = ~scl_padoen_o ? scl_pad_o : 1'bz;
reg i2c_read_req;
wire i2c_read_req_ack;
reg i2c_write_req;
wire i2c_write_req_ack;
wire[7:0] i2c_slave_dev_addr;
wire[15:0] i2c_slave_reg_addr;
wire[7:0] i2c_write_data;
wire[7:0] i2c_read_data;
wire err;
reg[2:0] state;
localparam S_IDLE = 0;
localparam S_WR_I2C_CHECK = 1;
localparam S_WR_I2C = 2;
localparam S_WR_I2C_DONE = 3;
assign done = (state == S_WR_I2C_DONE);
assign i2c_slave_dev_addr = lut_dev_addr;
assign i2c_slave_reg_addr = lut_reg_addr;
assign i2c_write_data = lut_reg_data;
//cascatrix carson
always@(posedge clk or posedge rst)
begin
if(rst)
begin
state <= S_IDLE;
error <= 1'b0;
lut_index <= 8'd0;
end
else
case(state)
S_IDLE:
begin
state <= S_WR_I2C_CHECK;
error <= 1'b0;
lut_index <= 8'd0;
end
S_WR_I2C_CHECK:
begin
if(i2c_slave_dev_addr != 8'hff)
begin
i2c_write_req <= 1'b1;
state <= S_WR_I2C;
end
else
begin
state <= S_WR_I2C_DONE;
end
end
S_WR_I2C:
begin
if(i2c_write_req_ack)
begin
error <= err ? 1'b1 : error;
lut_index <= lut_index + 8'd1;
i2c_write_req <= 1'b0;
state <= S_WR_I2C_CHECK;
end
end
S_WR_I2C_DONE:
begin
state <= S_WR_I2C_DONE;
end
default:
state <= S_IDLE;
endcase
end
i2c_ctrl i2c_ctrl
(
.rst(rst),
.clk(clk),
.clk_div_cnt(clk_div_cnt),
// I2C signals
// i2c clock line
.scl_pad_i(scl_pad_i), // SCL-line input
.scl_pad_o(scl_pad_o), // SCL-line output (always 1'b0)
.scl_padoen_o(scl_padoen_o), // SCL-line output enable (active low)
// i2c data line
.sda_pad_i(sda_pad_i), // SDA-line input
.sda_pad_o(sda_pad_o), // SDA-line output (always 1'b0)
.sda_padoen_o(sda_padoen_o), // SDA-line output enable (active low)
.i2c_read_req(i2c_read_req),
.i2c_addr_2byte(i2c_addr_2byte),
.i2c_read_req_ack(i2c_read_req_ack),
.i2c_write_req(i2c_write_req),
.i2c_write_req_ack(i2c_write_req_ack),
.i2c_slave_dev_addr(i2c_slave_dev_addr),
.i2c_slave_reg_addr(i2c_slave_reg_addr),
.i2c_write_data(i2c_write_data),
.i2c_read_data(i2c_read_data),
.error(err)
);
endmodule
2. 组帧模块 (i2c_ctrl)：
module i2c_ctrl
(
input rst,
input clk,
input[15:0] clk_div_cnt,
// I2C signals
// i2c clock line
input scl_pad_i, //SCL-line input
output scl_pad_o, //SCL-line output (always 1'b0)
output scl_padoen_o, //SCL-line output enable (active low)
// i2c data line
input sda_pad_i, //SDA-line input
output sda_pad_o, //SDA-line output (always 1'b0)
output sda_padoen_o, //SDA-line output enable (active low)
input i2c_addr_2byte, //register address 16bit or 8bit
input i2c_read_req, //Read register request
output i2c_read_req_ack, //Read register request response
input i2c_write_req, //Write register request
output i2c_write_req_ack, //Write register request response
input[7:0] i2c_slave_dev_addr, //I2c device address
input[15:0] i2c_slave_reg_addr, //I2c register address
input[7:0] i2c_write_data, //I2c write register data
output reg[7:0] i2c_read_data,//I2c read register data
output reg error //The error indication, generally there is no response
);
//State machine definition cascatrix carson
localparam S_IDLE= 0;
localparam S_WR_DEV_ADDR=1;
localparam S_WR_REG_ADDR=2;
localparam S_WR_DATA=3;
localparam S_WR_ACK=4;
localparam S_WR_ERR_NACK=5;
localparam S_RD_DEV_ADDR0=6;
localparam S_RD_REG_ADDR=7;
localparam S_RD_DEV_ADDR1=8;
localparam S_RD_DATA=9;
localparam S_RD_STOP=10;
localparam S_WR_STOP=11;
localparam S_WAIT=12;
localparam S_WR_REG_ADDR1=13;
localparam S_RD_REG_ADDR1=14;
localparam S_RD_ACK=15;
reg start;
reg stop;
reg read;
reg write;
reg ack_in;
reg[7:0] txr;
wire[7:0] rxr;
wire i2c_busy;
wire i2c_al;
wire done;
wire irxack;
reg[3:0] state, next_state;
assign i2c_read_req_ack = (state == S_RD_ACK);
assign i2c_write_req_ack = (state == S_WR_ACK);
always@(posedge clk or posedge rst)
begin
if(rst)
state <= S_IDLE;
else
state <= next_state;
end
always@(*)
begin
case(state)
S_IDLE:
//Waiting for read and write requests
if(i2c_write_req)
next_state <= S_WR_DEV_ADDR;
else if(i2c_read_req)
next_state <= S_RD_DEV_ADDR0;
else
next_state <= S_IDLE;
//Write I2C device address
S_WR_DEV_ADDR:
if(done && irxack)
next_state <= S_WR_ERR_NACK;
else if(done)
next_state <= S_WR_REG_ADDR;
else
next_state <= S_WR_DEV_ADDR;
//Write the address of the I2C register
S_WR_REG_ADDR:
if(done)
//If it is the 8bit register address, it enters the write data state
next_state<=i2c_addr_2byte? S_WR_REG_AD DR1 : S_WR_DATA;
else
next_state <= S_WR_REG_ADDR;
S_WR_REG_ADDR1:
if(done)
next_state <= S_WR_DATA;
else
next_state <= S_WR_REG_ADDR1;
//Write data
S_WR_DATA:
if(done)
next_state <= S_WR_STOP;
else
next_state <= S_WR_DATA;
S_WR_ERR_NACK:
next_state <= S_WR_STOP;
S_RD_ACK,S_WR_ACK:
next_state <= S_WAIT;
S_WAIT:
next_state <= S_IDLE;
S_RD_DEV_ADDR0:
if(done && irxack)
next_state <= S_WR_ERR_NACK;
else if(done)
next_state <= S_RD_REG_ADDR;
else
next_state <= S_RD_DEV_ADDR0;
S_RD_REG_ADDR:
if(done)
next_state<=i2c_addr_2byte?S_RD_REG_ADDR1 : S_RD_DEV_ADDR1;
else
next_state <= S_RD_REG_ADDR;
S_RD_REG_ADDR1:
if(done)
next_state <= S_RD_DEV_ADDR1;
else
next_state <= S_RD_REG_ADDR1;
S_RD_DEV_ADDR1:
if(done)
next_state <= S_RD_DATA;
else
next_state <= S_RD_DEV_ADDR1;
S_RD_DATA:
if(done)
next_state <= S_RD_STOP;
else
next_state <= S_RD_DATA;
S_RD_STOP:
if(done)
next_state <= S_RD_ACK;
else
next_state <= S_RD_STOP;
S_WR_STOP:
if(done)
next_state <= S_WR_ACK;
else
next_state <= S_WR_STOP;
default:
next_state <= S_IDLE;
endcase
end
always@(posedge clk or posedge rst)
begin
if(rst)
error <= 1'b0;
else if(state == S_IDLE)
error <= 1'b0;
else if(state == S_WR_ERR_NACK)
error <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
start <= 1'b0;
else if(done)
start <= 1'b0;
else if(state == S_WR_DEV_ADDR || state == S_RD_DEV_ADDR0 || state == S_RD_DEV_ADDR1)
start <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
stop <= 1'b0;
else if(done)
stop <= 1'b0;
else if(state == S_WR_STOP || state == S_RD_STOP)
stop <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
ack_in <= 1'b0;
else
ack_in <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
write <= 1'b0;
else if(done)
write <= 1'b0;
else if(state == S_WR_DEV_ADDR || state == S_WR_REG_ADDR || state == S_WR_REG_ADDR1|| state == S_WR_DATA || state == S_RD_DEV_ADDR0 || state == S_RD_DEV_ADDR1 || state == S_RD_REG_ADDR || state == S_RD_REG_ADDR1)
write <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
read <= 1'b0;
else if(done)
read <= 1'b0;
else if(state == S_RD_DATA)
read <= 1'b1;
end
always@(posedge clk or posedge rst)
begin
if(rst)
i2c_read_data <= 8'h00;
else if(state == S_RD_DATA && done)
i2c_read_data <= rxr;
end
always@(posedge clk or posedge rst)
begin
if(rst)
txr <= 8'd0;
else
case(state)
S_WR_DEV_ADDR,S_RD_DEV_ADDR0:
txr <= {i2c_slave_dev_addr[7:1],1'b0};
S_RD_DEV_ADDR1:
txr <= {i2c_slave_dev_addr[7:1],1'b1};
S_WR_REG_ADDR,S_RD_REG_ADDR:
txr<=(i2c_addr_2byte==1'b1)?i2c_slave_reg_addr[15 :8] : i2c_slave_reg_addr[7:0];
S_WR_REG_ADDR1,S_RD_REG_ADDR1:
txr <= i2c_slave_reg_addr[7:0];
S_WR_DATA:
txr <= i2c_write_data;
default:
txr <= 8'hff;
endcase
end
i2c_byte_ctrl byte_controller (
.clk ( clk ),
.rst ( rst ),
.nReset ( 1'b1 ),
.ena ( 1'b1 ),
.clk_cnt ( clk_div_cnt ),
.start ( start ),
.stop ( stop ),
.read ( read ),
.write ( write ),
.ack_in ( ack_in ),
.din ( txr ),
.cmd_ack ( done ),
.ack_out ( irxack ),
.dout ( rxr ),
.i2c_busy ( i2c_busy ),
.i2c_al ( i2c_al ),
.scl_i ( scl_pad_i ),
.scl_o ( scl_pad_o ),
.scl_oen ( scl_padoen_o ),
.sda_i ( sda_pad_i ),
.sda_o ( sda_pad_o ),
.sda_oen ( sda_padoen_o )
);
endmodule
3. 字节控制模块（i2c_byte_ctrl）:
`define I2C_CMD_NOP 4'b0000
`define I2C_CMD_START 4'b0001
`define I2C_CMD_STOP 4'b0010
`define I2C_CMD_WRITE 4'b0100
`define I2C_CMD_READ 4'b1000
module i2c_byte_ctrl (
input clk, // master clock
input rst, // synchronous active high reset
input nReset, // asynchronous active low reset
input ena, // core enable signal
input [15:0] clk_cnt, // 4x SCL
// control inputs
input start,
input stop,
input read,
input write,
input ack_in,
input [7:0] din,
// status outputs
output reg cmd_ack,
output regack_out,
output i2c_busy,
output i2c_al,
output [7:0] dout,
// I2C signals
input scl_i,
output scl_o,
output scl_oen,
input sda_i,
output sda_o,
output sda_oen
);
//
// Variable declarations cascatrix carson
//
// statemachine
parameter [4:0] ST_IDLE = 5'b0_0000;
parameter [4:0] ST_START = 5'b0_0001;
parameter [4:0] ST_READ = 5'b0_0010;
parameter [4:0] ST_WRITE = 5'b0_0100;
parameter [4:0] ST_ACK = 5'b0_1000;
parameter [4:0] ST_STOP = 5'b1_0000;
// signals for bit_controller
reg [3:0] core_cmd;
reg core_txd;
wire core_ack, core_rxd;
// signals for shift register
reg [7:0] sr; //8bit shift register
reg shift, ld;
// signals for state machine
wire go;
reg [2:0] dcnt;
wire cnt_done;
// bit_controller
i2c_bit_ctrl bit_controller (
.clk ( clk ),
.rst ( rst ),
.nReset ( nReset ),
.ena ( ena ),
.clk_cnt ( clk_cnt ),
.cmd ( core_cmd ),
.cmd_ack ( core_ack ),
.busy ( i2c_busy ),
.al ( i2c_al ),
.din ( core_txd ),
.dout ( core_rxd ),
.scl_i ( scl_i ),
.scl_o ( scl_o ),
.scl_oen ( scl_oen ),
.sda_i ( sda_i ),
.sda_o ( sda_o ),
.sda_oen ( sda_oen )
);
// generate go-signal
assign go = (read | write | stop) & ~cmd_ack;
// assign dout output to shift-register
assign dout = sr;
// generate shift register
always @(posedge clk or negedge nReset)
if (!nReset)
sr <= #1 8'h0;
else if (rst)
sr <= #1 8'h0;
else if (ld)
sr <= #1 din;
else if (shift)
sr <= #1 {sr[6:0], core_rxd};
// generate counter
always @(posedge clk or negedge nReset)
if (!nReset)
dcnt <= #1 3'h0;
else if (rst)
dcnt <= #1 3'h0;
else if (ld)
dcnt <= #1 3'h7;
else if (shift)
dcnt <= #1 dcnt - 3'h1;
assign cnt_done = ~(|dcnt);
//
// state machine
//
reg [4:0] c_state; // synopsys enum_state
always @(posedge clk or negedge nReset)
if (!nReset)
begin
core_cmd <= #1 `I2C_CMD_NOP;
core_txd <= #1 1'b0;
shift <= #1 1'b0;
ld <= #1 1'b0;
cmd_ack <= #1 1'b0;
c_state <= #1 ST_IDLE;
ack_out <= #1 1'b0;
end
else if (rst | i2c_al)
begin
core_cmd <= #1 `I2C_CMD_NOP;
core_txd <= #1 1'b0;
shift <= #1 1'b0;
ld <= #1 1'b0;
cmd_ack <= #1 1'b0;
c_state <= #1 ST_IDLE;
ack_out <= #1 1'b0;
end
else
begin
// initially reset all signals
core_txd <= #1 sr[7];
shift <= #1 1'b0;
ld <= #1 1'b0;
cmd_ack <= #1 1'b0;
case (c_state) // synopsys full_case parallel_case
ST_IDLE:
if (go)
begin
if (start)
begin
c_state <= #1 ST_START;
core_cmd <= #1 `I2C_CMD_START;
end
else if (read)
begin
c_state <= #1 ST_READ;
core_cmd <= #1 `I2C_CMD_READ;
end
else if (write)
begin
c_state <= #1 ST_WRITE;
core_cmd <= #1 `I2C_CMD_WRITE;
end
else // stop
begin
c_state <= #1 ST_STOP;
core_cmd <= #1 `I2C_CMD_STOP;
end
ld <= #1 1'b1;
end
ST_START:
if (core_ack)
begin
if (read)
begin
c_state <= #1 ST_READ;
core_cmd <= #1 `I2C_CMD_READ;
end
else
begin
c_state <= #1 ST_WRITE;
core_cmd <= #1 `I2C_CMD_WRITE;
end
ld <= #1 1'b1;
end
ST_WRITE:
if (core_ack)
if (cnt_done)
begin
c_state <= #1 ST_ACK;
core_cmd <= #1 `I2C_CMD_READ;
end
else
begin
// stay in same state
c_state <= #1 ST_WRITE;
// write next bit
core_cmd <= #1 `I2C_CMD_WRITE;
shift <= #1 1'b1;
end
ST_READ:
if (core_ack)
begin
if (cnt_done)
begin
c_state <= #1 ST_ACK;
core_cmd <= #1 `I2C_CMD_WRITE;
end
else
begin
// stay in same state
c_state <= #1 ST_READ;
// read next bit
core_cmd <= #1 `I2C_CMD_READ;
end
shift <= #1 1'b1;
core_txd <= #1 ack_in;
end
ST_ACK:
if (core_ack)
begin
if (stop)
begin
c_state <= #1 ST_STOP;
core_cmd <= #1 `I2C_CMD_STOP;
end
else
begin
c_state <= #1 ST_IDLE;
core_cmd <= #1 `I2C_CMD_NOP;
// generate command acknowledge signal
cmd_ack <= #1 1'b1;
end
// assign ack_out output to bit_controller_rxd (contains last received bit)
ack_out <= #1 core_rxd;
core_txd <= #1 1'b1;
end
else
core_txd <= #1 ack_in;
ST_STOP:
if (core_ack)
begin
c_state <= #1 ST_IDLE;
core_cmd <= #1 `I2C_CMD_NOP;
// generate command acknowledge signal
cmd_ack <= #1 1'b1;
end
endcase
end
endmodule
4. bit控制模块（i2c_bit_ctrl）:
`define I2C_CMD_NOP 4'b0000
`define I2C_CMD_START 4'b0001
`define I2C_CMD_STOP 4'b0010
`define I2C_CMD_WRITE 4'b0100
`define I2C_CMD_READ 4'b1000
module i2c_bit_ctrl (
input clk, // system clock
input rst, // synchronous active high reset
input nReset, // asynchronous active low reset
input ena, // core enable signal
input [15:0] clk_cnt, // clock prescale value
input [ 3:0] cmd, // command (from byte controller)
output reg cmd_ack, // command complete acknowledge
output reg busy, // i2c bus busy
output reg al, // i2c bus arbitration lost
input din,
output reg dout,
input scl_i, // i2c clock line input
output scl_o, // i2c clock line output
output reg scl_oen, // i2c clock line output enable (active low)
input sda_i, // i2c data line input
output sda_o, // i2c data line output
output reg sda_oen // i2c data line output enable (active low)
);
//
// variable declarations
//
reg [ 1:0] cSCL, cSDA; // capture SCL and SDA
reg [ 2:0] fSCL, fSDA; // SCL and SDA filter inputs
reg sSCL, sSDA; // filtered and synchronized SCL and SDA inputs
reg dSCL, dSDA; // delayed versions of sSCL and sSDA
reg dscl_oen; // delayed scl_oen
reg sda_chk; // check SDA output (Multi-master arbitration)
reg clk_en; // clock generation signals
reg slave_wait; // slave inserts wait states
reg [15:0] cnt; // clock divider counter (synthesis)
reg [13:0] filter_cnt; // clock divider for filter
// state machine variable
reg [17:0] c_state; // synopsys enum_state
//
// module body
//
// whenever the slave is not ready it can delay the cycle by pulling SCL low
// delay scl_oen
always @(posedge clk)
dscl_oen <= #1 scl_oen;
// slave_wait is asserted when master wants to drive SCL high, but the slave pulls it low
// slave_wait remains asserted until the slave releases SCL
always @(posedge clk or negedge nReset)
if (!nReset) slave_wait <= 1'b0;
else slave_wait <= (scl_oen & ~dscl_oen & ~sSCL) | (slave_wait & ~sSCL);
// master drives SCL high, but another master pulls it low
// master start counting down its low cycle now (clock synchronization)
wire scl_sync = dSCL & ~sSCL & scl_oen;
// generate clk enable signal
always @(posedge clk or negedge nReset)
if (~nReset)
begin
cnt <= #1 16'h0;
clk_en <= #1 1'b1;
end
else if (rst || ~|cnt || !ena || scl_sync)
begin
cnt <= #1 clk_cnt;
clk_en <= #1 1'b1;
end
else if (slave_wait)
begin
cnt <= #1 cnt;
clk_en <= #1 1'b0;
end
else
begin
cnt <= #1 cnt - 16'h1;
clk_en <= #1 1'b0;
end
// generate bus status controller
// capture SDA and SCL
// reduce metastability risk
always @(posedge clk or negedge nReset)
if (!nReset)
begin
cSCL <= #1 2'b00;
cSDA <= #1 2'b00;
end
else if (rst)
begin
cSCL <= #1 2'b00;
cSDA <= #1 2'b00;
end
else
begin
cSCL <= {cSCL[0],scl_i};
cSDA <= {cSDA[0],sda_i};
end
// filter SCL and SDA signals; (attempt to) remove glitches
always @(posedge clk or negedge nReset)
if (!nReset ) filter_cnt <= 14'h0;
else if (rst || !ena ) filter_cnt <= 14'h0;
else if (~|filter_cnt) filter_cnt <= clk_cnt >> 2; //16x I2C bus frequency
else filter_cnt <= filter_cnt -1;
always @(posedge clk or negedge nReset)
if (!nReset)
begin
fSCL <= 3'b111;
fSDA <= 3'b111;
end
else if (rst)
begin
fSCL <= 3'b111;
fSDA <= 3'b111;
end
else if (~|filter_cnt)
begin
fSCL <= {fSCL[1:0],cSCL[1]};
fSDA <= {fSDA[1:0],cSDA[1]};
end
// generate filtered SCL and SDA signals
always @(posedge clk or negedge nReset)
if (~nReset)
begin
sSCL <= #1 1'b1;
sSDA <= #1 1'b1;
dSCL <= #1 1'b1;
dSDA <= #1 1'b1;
end
else if (rst)
begin
sSCL <= #1 1'b1;
sSDA <= #1 1'b1;
dSCL <= #1 1'b1;
dSDA <= #1 1'b1;
end
else
begin
sSCL <= #1 &fSCL[2:1] | &fSCL[1:0] | (fSCL[2] & fSCL[0]);
sSDA <= #1 &fSDA[2:1] | &fSDA[1:0] | (fSDA[2] & fSDA[0]);
dSCL <= #1 sSCL;
dSDA <= #1 sSDA;
end
// detect start condition => detect falling edge on SDA while SCL is high
// detect stop condition => detect rising edge on SDA while SCL is high
reg sta_condition;
reg sto_condition;
always @(posedge clk or negedge nReset)
if (~nReset)
begin
sta_condition <= #1 1'b0;
sto_condition <= #1 1'b0;
end
else if (rst)
begin
sta_condition <= #1 1'b0;
sto_condition <= #1 1'b0;
end
else
begin
sta_condition <= #1 ~sSDA & dSDA & sSCL;
sto_condition <= #1 sSDA & ~dSDA & sSCL;
end
// generate i2c bus busy signal
always @(posedge clk or negedge nReset)
if (!nReset) busy <= #1 1'b0;
else if (rst ) busy <= #1 1'b0;
else busy <= #1 (sta_condition | busy) & ~sto_condition;
// generate arbitration lost signal cascatrix carson
// aribitration lost when:
// 1) master drives SDA high, but the i2c bus is low
// 2) stop detected while not requested
reg cmd_stop;
always @(posedge clk or negedge nReset)
if (~nReset)
cmd_stop <= #1 1'b0;
else if (rst)
cmd_stop <= #1 1'b0;
else if (clk_en)
cmd_stop <= #1 cmd == `I2C_CMD_STOP;
always @(posedge clk or negedge nReset)
if (~nReset)
al <= #1 1'b0;
else if (rst)
al <= #1 1'b0;
else
al <= #1 (sda_chk & ~sSDA & sda_oen) | (|c_state & sto_condition & ~cmd_stop);
// generate dout signal (store SDA on rising edge of SCL) cascatrix carson
always @(posedge clk)
if (sSCL & ~dSCL) dout <= #1 sSDA;
// generate statemachine cascatrix carson
// nxt_state decoder
parameter [17:0] idle = 18'b0_0000_0000_0000_0000;
parameter [17:0] start_a = 18'b0_0000_0000_0000_0001;
parameter [17:0] start_b = 18'b0_0000_0000_0000_0010;
parameter [17:0] start_c = 18'b0_0000_0000_0000_0100;
parameter [17:0] start_d = 18'b0_0000_0000_0000_1000;
parameter [17:0] start_e = 18'b0_0000_0000_0001_0000;
parameter [17:0] stop_a = 18'b0_0000_0000_0010_0000;
parameter [17:0] stop_b = 18'b0_0000_0000_0100_0000;
parameter [17:0] stop_c = 18'b0_0000_0000_1000_0000;
parameter [17:0] stop_d = 18'b0_0000_0001_0000_0000;
parameter [17:0] rd_a = 18'b0_0000_0010_0000_0000;
parameter [17:0] rd_b = 18'b0_0000_0100_0000_0000;
parameter [17:0] rd_c = 18'b0_0000_1000_0000_0000;
parameter [17:0] rd_d = 18'b0_0001_0000_0000_0000;
parameter [17:0] wr_a = 18'b0_0010_0000_0000_0000;
parameter [17:0] wr_b = 18'b0_0100_0000_0000_0000;
parameter [17:0] wr_c = 18'b0_1000_0000_0000_0000;
parameter [17:0] wr_d = 18'b1_0000_0000_0000_0000;
always @(posedge clk or negedge nReset)
if (!nReset)
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b0;
scl_oen <= #1 1'b1;
sda_oen <= #1 1'b1;
sda_chk <= #1 1'b0;
end
else if (rst | al)
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b0;
scl_oen <= #1 1'b1;
sda_oen <= #1 1'b1;
sda_chk <= #1 1'b0;
end
else
begin
// default no command acknowledge + assert cmd_ack only 1clk cycle
cmd_ack <= #1 1'b0;
if (clk_en)// synopsys full_case parallel_case
case (c_state)
// idle state
idle:
begin// synopsys full_case parallel_case
case (cmd)
`I2C_CMD_START: c_state <= #1 start_a;
`I2C_CMD_STOP: c_state <= #1 stop_a;
`I2C_CMD_WRITE: c_state <= #1 wr_a;
`I2C_CMD_READ: c_state <= #1 rd_a;
default: c_state <= #1 idle;
endcase
// keep SCL in same state
scl_oen <= #1 scl_oen;
// keep SDA in same state
sda_oen <= #1 sda_oen;
// don't check SDA output
sda_chk <= #1 1'b0;
end
// start
start_a:
begin
c_state <= #1 start_b;
// keep SCL in same state
scl_oen <= #1 scl_oen;
sda_oen <= #1 1'b1; // set SDA high
// don't check SDA output
sda_chk <= #1 1'b0;
end
start_b:
begin
c_state <= #1 start_c;
scl_oen <= #1 1'b1; // set SCL high
sda_oen <= #1 1'b1; // keep SDA high
// don't check SDA output
sda_chk <= #1 1'b0;
end
start_c:
begin
c_state <= #1 start_d;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 1'b0; // set SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
start_d:
begin
c_state <= #1 start_e;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 1'b0; // keep SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
start_e:
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b1;
scl_oen <= #1 1'b0; // set SCL low
sda_oen <= #1 1'b0; // keep SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
// stop
stop_a:
begin
c_state <= #1 stop_b;
scl_oen <= #1 1'b0; // keep SCL low
sda_oen <= #1 1'b0; // set SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
stop_b:
begin
c_state <= #1 stop_c;
scl_oen <= #1 1'b1; // set SCL high
sda_oen <= #1 1'b0; // keep SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
stop_c:
begin
c_state <= #1 stop_d;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 1'b0; // keep SDA low
// don't check SDA output
sda_chk <= #1 1'b0;
end
stop_d:
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b1;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 1'b1; // set SDA high
// don't check SDA output
sda_chk <= #1 1'b0;
end
// read
rd_a:
begin
c_state <= #1 rd_b;
scl_oen <= #1 1'b0; // keep SCL low
sda_oen <= #1 1'b1; // tri-state SDA
// don't check SDA output
sda_chk <= #1 1'b0;
end
rd_b:
begin
c_state <= #1 rd_c;
scl_oen <= #1 1'b1; // set SCL high
sda_oen <= #1 1'b1; // keep SDA tri-stated
// don't check SDA output
sda_chk <= #1 1'b0;
end
rd_c:
begin
c_state <= #1 rd_d;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 1'b1; // keep SDA tri-stated
// don't check SDA output
sda_chk <= #1 1'b0;
end
rd_d:
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b1;
scl_oen <= #1 1'b0; // set SCL low
sda_oen <= #1 1'b1; // keep SDA tri-stated
// don't check SDA output
sda_chk <= #1 1'b0;
end
// write
wr_a:
begin
c_state <= #1 wr_b;
scl_oen <= #1 1'b0; // keep SCL low
sda_oen <= #1 din; // set SDA
// don't check SDA output (SCL low)
sda_chk <= #1 1'b0;
end
wr_b:
begin
c_state <= #1 wr_c;
scl_oen <= #1 1'b1; // set SCL high
sda_oen <= #1 din; // keep SDA
// don't check SDA output yet
sda_chk <= #1 1'b0;
// allow some time for SDA and SCL to settle
end
wr_c:
begin
c_state <= #1 wr_d;
scl_oen <= #1 1'b1; // keep SCL high
sda_oen <= #1 din;
sda_chk <= #1 1'b1; // check SDA output
end
wr_d:
begin
c_state <= #1 idle;
cmd_ack <= #1 1'b1;
scl_oen <= #1 1'b0; // set SCL low
sda_oen <= #1 din;
sda_chk <= #1 1'b0; // don't check SDA output (SCL low)
end
endcase
end
// assign scl and sda output (always gnd)
assign scl_o = 1'b0;
assign sda_o = 1'b0;
endmodule
04
IIC的优缺点
4.1 IIC协议优点
1. 通信只需要两条信号线；
2. 多主设备结构下，总线系统无需额外的逻辑与线路；
3. 应答机制完善，通信传输稳定。
4.2 IIC协议缺点
1. 硬件结构复杂；
2. 支持传输距离较短；
3. 半双工速率慢于全双工，SPI全双工一般可实现10Mbps以上的传输速率，IIC最高速度仅能达到3.4Mbps。
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原文标题：常用串行总线(三)——IIC协议(Verilog实现)
文章出处：【微信号：Carlinx FPGA，微信公众号：Carlinx FPGA】欢迎添加关注！文章转载请注明出处。
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