如何在 XILINX FPGA (Artix-7) 上实现 HDMI 直通

Question

我想在配备 Artix-7 FPGA 和 HDMI 接收/源端口的 Nexys-Video Board 上实现我自己的 HDMI-Passthrough。我的设置是：PC HDMI 端口连接到接收端口，而 LED 监视器连接到源 HDMI 端口。

由于板上没有 TDMS 编码器/解码器，接下来我还需要实现它们（我不想只获取互联网上现成的封闭源代码实现之一）。但是现在，我只需要通过 FPGA 连接接收器/源端口，这样我就可以在监视器上显示视频。但是，我还没有成功。没有显示图片，显示器显示“无信号”。我有点担心滥用 FGPA 端口可能会导致电路板永久性损坏。因此，我没有尝试一切都浮现在我的脑海中。我期待建议以更正/完成我的代码。

我按照以下代码和原理图连接了 HDMI 信号：

module HDMI_Top(RSTN, CLK, BTN, SW, LED,
            HDMIR_TXEN, HDMIR_HPA, HDMIT_HPD, 
            HDMIR_SCL, HDMIR_SDA, HDMIT_SCL, HDMIT_SDA,
            HDMIR_CLK_P, HDMIR_CLK_N, HDMIR_DATA_P, HDMIR_DATA_N,
            HDMIT_CLK_P, HDMIT_CLK_N, HDMIT_DATA_P, HDMIT_DATA_N);

input RSTN;
input CLK;
input [4:0] BTN;
input [7:0] SW;
output [7:0] LED;

output HDMIR_TXEN;
output HDMIR_HPA;
input HDMIT_HPD;
inout HDMIR_SCL;
inout HDMIR_SDA;
inout HDMIT_SCL;
inout HDMIT_SDA;

input HDMIR_CLK_P;
input HDMIR_CLK_N;
input [2:0] HDMIR_DATA_P;
input [2:0] HDMIR_DATA_N;
output HDMIT_CLK_P;
output HDMIT_CLK_N;
output [2:0] HDMIT_DATA_P;
output [2:0] HDMIT_DATA_N;

wire [2:0] HDMI_DATA;
wire HDMI_CLK;
wire w0, w1, w2;

assign LED = SW;
//assign HDMIR_HPA = HDMIT_HPD;
assign HDMIR_TXEN = 1'b1;
assign HDMIT_SCL = HDMIR_SCL;
assign HDMIT_SDA = HDMIR_SDA;

// IBUFDS: Differential Input Buffer
IBUFDS #(
    .DIFF_TERM("FALSE"), // Differential Termination
    .IOSTANDARD("DEFAULT") // Specify the input I/O standard
) IBUFDS_hdmir_clk (
    .O(HDMI_CLK), // Buffer output
    .I(HDMIR_CLK_P), // Diff_p buffer input (connect directly to top-level port)
    .IB(HDMIR_CLK_N) // Diff_n buffer input (connect directly to top-level port)
);

OBUFDS #(
    .IOSTANDARD("DEFAULT") // Specify the output I/O standard
) OBUFDS_hdmit_clk (
    .O(HDMIT_CLK_P), // Diff_p output (connect directly to top-level port)
    .OB(HDMIT_CLK_N), // Diff_n output (connect directly to top-level port)
    .I(HDMI_CLK) // Buffer input
);

// IBUFDS: Differential Input Buffer
IBUFDS #(
    .DIFF_TERM("FALSE"), // Differential Termination
    .IOSTANDARD("DEFAULT") // Specify the input I/O standard
) IBUFDS_hdmir_data [2:0] (
    .O(HDMI_DATA), // Buffer output
    .I(HDMIR_DATA_P), // Diff_p buffer input (connect directly to top-level port)
    .IB(HDMIR_DATA_N) // Diff_n buffer input (connect directly to top-level port)
);

OBUFDS #(
    .IOSTANDARD("DEFAULT") // Specify the output I/O standard
) OBUFDS_hdmit_data [2:0] (
    .O(HDMIT_DATA_P), // Diff_p output (connect directly to top-level port)
    .OB(HDMIT_DATA_N), // Diff_n output (connect directly to top-level port)
    .I(HDMI_DATA) // Buffer input
);endmodule

Here是代码对应的原理图。

谢谢；

Answer 1

我终于让它工作了。现在我的 Nexys 显卡可以通过全高清视频。以下是详细信息：

1. HPA 和 TXEN 引脚都必须设置为“1”。在我的例子中，我将源端口的 HPD 引脚分配给接收端口的 HPA 引脚。检查电路板原理图，HPD 引脚连接到开漏 MOSFET，因此在分配之前必须将其反转。

分配 HDMIR_HPA = ~HDMIT_HPD;

1. 此外，经过彻底的谷歌搜索，我发现将接收端口的 DDC SCL 和 SDA 引脚桥接到源端口似乎是不可能的，因为两个双向引脚不能（简单）连接到 FPGA 上。所以解决问题的方法是在 sink 端添加一个 EDID ROM 仿真器。然后 FPGA 本身充当视频源设备（即我设置中的 PC）的监视器。

我从here 找到了 EDID ROM 的 VHDL 实现。它模拟 1024 x 768 显示器，但我将其更改为 1920 x 1080。

这是顶层模块的修改代码：

module HDMI_Top(
input RSTN,
input CLK,
input [4:0] BTN,
input [7:0] SW,
output [7:0] LED,
output HDMIR_TXEN,
output HDMIR_HPA,
input HDMIT_HPD, 
input HDMIR_SCL,
inout HDMIR_SDA,
output HDMIT_SCL,
inout HDMIT_SDA,
input HDMIR_CLK_P,
input HDMIR_CLK_N,
input [2:0] HDMIR_DATA_P,
input [2:0] HDMIR_DATA_N,
output HDMIT_CLK_P,
output HDMIT_CLK_N,
output [2:0] HDMIT_DATA_P,
output [2:0] HDMIT_DATA_N
);

wire HDMI_CLK;
wire [2:0] HDMI_DATA;

assign LED = SW;

// Whenever a sink is ready and wishes to announce its presence, it connects the 5V0 supply pin to the HPD pin. On
// the Nexys Video, this is done by driving the HPA (Hot Plug Assert) signal high. Note: this should only be done
// after a DDC channel slave has been implemented in the FPGA and is ready to transmit display data.
// FPGA lets the HDMI source (e.g., a PC) connected to its sink port know its presence by setting HPA signal to '1'.
// A monitor connected to the source port sets HPD signal to '0'.
// assign HDMIR_HPA = 1'b1;
assign HDMIR_HPA = ~HDMIT_HPD;

// A pull-down resistor on the TXEN signal makes sure the sink buffer's transmitter facing the FPGA is disabled by default.
// An FPGA design using the sink port needs to actively drive this pin high for the buffer to pass data through.
assign HDMIR_TXEN = 1'b1;

// The Display Data Channel, or DDC, is a collection of protocols that enable communication between the display
// (sink) and graphics adapter (source). The DDC2B variant is based on I2C, the bus master being the source and the
// bus slave the sink. When a source detects high level on the HPD pin, it queries the sink over the DDC bus for video
// capabilities. It determines whether the sink is DVI or HDMI-capable and what resolutions are supported. Only
// afterwards will video transmission begin. Refer to VESA E-DDC specifications for more information.
edid_rom edid_rom_rx0 (.clk(CLK), .sclk_raw(HDMIR_SCL), .sdat_raw(HDMIR_SDA));
    
// IBUFDS: Differential Input Buffer
IBUFDS #(
    .DIFF_TERM("FALSE"), // Differential Termination
    .IOSTANDARD("DEFAULT") // Specify the input I/O standard
) IBUFDS_hdmir_clk (
    .O(HDMI_CLK), // Buffer output
    .I(HDMIR_CLK_P), // Diff_p buffer input (connect directly to top-level port)
    .IB(HDMIR_CLK_N) // Diff_n buffer input (connect directly to top-level port)
);

OBUFDS #(
    .IOSTANDARD("DEFAULT") // Specify the output I/O standard
) OBUFDS_hdmit_clk (
    .O(HDMIT_CLK_P), // Diff_p output (connect directly to top-level port)
    .OB(HDMIT_CLK_N), // Diff_n output (connect directly to top-level port)
    .I(HDMI_CLK) // Buffer input
);

// IBUFDS: Differential Input Buffer
IBUFDS #(
    .DIFF_TERM("FALSE"), // Differential Termination
    .IOSTANDARD("DEFAULT") // Specify the input I/O standard
) IBUFDS_hdmir_data [2:0] (
    .O(HDMI_DATA), // Buffer output
    .I(HDMIR_DATA_P), // Diff_p buffer input (connect directly to top-level port)
    .IB(HDMIR_DATA_N) // Diff_n buffer input (connect directly to top-level port)
);

OBUFDS #(
    .IOSTANDARD("DEFAULT") // Specify the output I/O standard
) OBUFDS_hdmit_data [2:0] (
    .O(HDMIT_DATA_P), // Diff_p output (connect directly to top-level port)
    .OB(HDMIT_DATA_N), // Diff_n output (connect directly to top-level port)
    .I(HDMI_DATA) // Buffer input
); endmodule

你可以找到完整的源代码here。

我的下一步是将串行器/解串器和 tmds 编码器/解码器添加到项目中。对于那些可能希望做同样事情的人，here 是我（工作）源代码的最新版本，包括序列化器/解串器和 tmds 编码器/解码器。