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SystemVerilog code for HDMI 1.4b video/audio output on an FPGA.


Most free and open source HDMI source (computer/gaming console) implementations actually output a DVI signal, which HDMI sinks (TVs/monitors) are backwards compatible with. To support audio and other HDMI-only functionality, a true HDMI signal must be sent. The code in this repository lets you do that without having to license an HDMI IP block from anyone.

Demo: VGA-compatible text mode, 720x480p on a Dell Ultrasharp 1080p Monitor

GIF showing VGA-compatible text mode on a monitor


  1. Take files from src/ and add them to your own project. If you use hdlmake, you can add this repository itself as a remote module.
  2. Other helpful modules for displaying text / generating sound are also available in this GitHub organization.
  3. Consult the simple usage example in top/
  4. See hdmi-demo for code that runs the demo as seen the demo GIF.
  5. Read through the parameters in and tailor any instantiations to your situation.
  6. Please create an issue if you run into a problem or have any questions. Make sure you have consulted the troubleshooting section first.

Platform Support

To-do List (upon request)

  • 24-bit color
  • Data island packets
    • Null packet
    • ECC with BCH systematic encoding GF(2^8)
    • Audio clock regeneration
    • L-PCM audio
      • 2-channel
      • 3-channel to 8-channel
    • 1-bit audio
    • Audio InfoFrame
    • Auxiliary Video Information InfoFrame
    • Source Product Descriptor InfoFrame
    • MPEG Source InfoFrame
      • NOTE—Problems with the MPEG Source Infoframe have been identified that were not able to be fixed in time for CEA-861-D. Implementation is strongly discouraged until a future revision fixes the problems
    • Gamut Metadata
  • Video formats 1, 2, 3, 4, 16, 17, 18, and 19
  • VGA-compatible text mode
    • IBM 8x16 font
    • Alternate fonts
  • Other color formats (YCbCr, deep color, etc.)
  • Support other video id codes
    • Interlaced video
    • Pixel repetition

Pixel Clock

You'll need to set up a PLL for producing the two HDMI clocks. The pixel clock for each supported format is shown below:

Video Resolution Video ID Code(s) Refresh Rate Pixel Clock Frequency Progressive/Interlaced
640x480 1 60Hz 25.2MHz P
640x480 1 59.94Hz 25.175MHz P
720x480 2, 3 60Hz 27.027MHz P
720x480 2, 3 59.94Hz 27MHz P
720x576 17, 18 50Hz 27MHz P
1280x720 4 60Hz 74.25MHz P
1280x720 4 59.94Hz 74.176MHz P
1280x720 19 50Hz 74.25MHz P
1920x1080 16 60Hz 148.5MHz P
1920x1080 16 59.94Hz 148.352MHz P
1920x1080 34 30Hz 74.25MHz P
1920x1080 34 29.97Hz 74.176MHz P
3840x2160 (not ready) 97, 107 60Hz 594MHz P
3840x2160 95, 105 30Hz 297MHz P

The second clock is a clock 5 times as fast as the pixel clock. Even if your FPGA only has a single PLL, the Altera MegaWizard (or the Xilinx equivalent) should still be able to produce both. See hdl-util/hdmi-demo for example PLLs.

L-PCM Audio Bitrate / Sampling Frequency

Both audio bitrate and frequency are specified as parameters of the HDMI module. Bitrate can be any value from 16 through 24. Below is a simple mapping of sample frequency to the appropriate parameter

WARNING: the audio can be REALLY LOUD if you use the full dynamic range with hand-generated waveforms! Using less dynamic range means you won't be deafened! (i.e. audio_sample >> 8 )

Sampling Frequency AUDIO_RATE value
32 kHz 32000
44.1 kHz 44100
88.2 kHz 88200
176.4 kHz 176400
48 kHz 48000
96 kHz 96000
192 kHz 192000

Source Device Information Code

This code is sent in the Source Product Description InfoFrame via SOURCE_DEVICE_INFORMATION to give HDMI sinks an idea of what capabilities an HDMI source might have. It may be used for displaying a relevant icon in an input list (i.e. DVD logo for a DVD player).

Code Source Device Information
0x00 Unknown
0x01 Digital Set-top Box
0x02 DVD Player
0x03 Digital VHS
0x04 HDD Videorecorder
0x05 Digital Video Camera
0x06 Digital Still Camera
0x07 Video CD
0x08 Game
0x09 PC General
0x0a Blu-Ray Disc
0x0b Super Audio CD
0x0c HD DVD
0x0d Portable Media Player

Things to be aware of / Troubleshooting

  • Limited resolution: some FPGAs don't support I/O at speeds high enough to achieve 720p/1080p
    • Workaround: Altera FPGA users can try to specify speed grade C6 and see if it works, though yours may be C7 or C8. Beware that this might introduce some system instability.
  • FPGA does not support TMDS: many FPGAs without a dedicated HDMI output don't support TMDS
    • You should be able to directly use LVDS (3.3v) instead, tested up to 720x480
    • This might not work if your video has a high number of transitions or you plan to use higher resolutions
    • Solution: AC-couple the 3.3v LVDS wires to by adding 100nF capacitors in series, as close to the transmitter as possible
  • Poor wiring: if you're using a breakout board or long lengths of untwisted wire, there might be a few pixels that jitter due to interference
    • Make sure you have all the necessary pins connected (GND pins, etc.)
    • Try switching your HDMI cable; some cheap cables like these I got from Amazon have poor shielding
  • Hot-Plug unaware: all modules are unaware of hotplug
    • This shouldn't affect anything in the long term; the only stateful value is hdmi.tmds_channel[2:0].acc
    • You should decide hotplug behavior (i.e. pause/resume on disconnect/connect, or ignore it)
  • EDID not implemented: it is assumed you know what format you want at synthesis time, so there is no dynamic decision on video format
    • To be implemented in a display protocol independent manner
  • SCL/SCA voltage level: though unused by this is I2C on a 5V logic level, as confirmed in the TPD12S016 datasheet, which is unsupported by most FPGAs
    • Solution: use a bidirectional logic level shifter compatible with I2C to convert 3.3v LVTTL to 5v
    • Solution: use 3.3-V LVTTL I/O standard with 6.65k pull-up resistors to 3.3v (as done in J13 on the Arduino MKR Vivado 4000 schematic)
    • Emailed Arduino support: safe to use as long as the HDMI slave does not have pull-ups


Dual-licensed under Apache License 2.0 and MIT License.

HDMI Adoption

I am NOT a lawyer, the below advice is given based on discussion from a Hacker News post and my research.

HDMI itself is not a royalty free technology, unfortunately. You are free to use it for testing, development, etc. but to receive the HDMI LA's (licensing administration) blessing to create and sell end-user products:

The manufacturer of the finished end-user product MUST be a licensed HDMI Adopter, and The finished end-user product MUST satisfy all requirements as defined in the Adopter Agreement including but not limited to passing compliance testing either at an HDMI ATC or through self-testing.

Becoming an adopter means you have to pay a flat annual fee (~ $1k-$2k) and a per device royalty (~ $0.05). If you are selling an end-user device and DO NOT want to become an adopter, you can turn on the DVI_OUTPUT parameter, which will disable any HDMI-only logic, like audio.

Please consult your lawyer if you have any concerns. Here are a few noteworthy cases that may help you make a decision:

  • Arduino LLC is not an adopter, yet sells the Arduino MKR Vidor 4000 FPGA
    • It has a micro-HDMI connector
    • Having an HDMI connector does not require a license
    • Official examples provided by Arduino on GitHub only perform DVI output
    • It is a user's choice to program the FPGA for HDMI output
    • Therefore: the device isn't an end-user product under the purview of HDMI LA
  • Unlicensed DisplayPort to HDMI cables (2011)
  • Terminated Adopters
    • There are currently 1,043 terminated adopters
    • Includes noteworthy companies like Xilinx, Lattice Semiconductor, Cypress Semiconductor, EVGA (!), etc.
    • No conclusion
  • Raspberry Pi Trading Ltd is licensed
    • They include the HDMI logo for products
    • Therefore: Raspberry Pi products are legal, licensed end-user products

Alternative Implementations

If you know of another good alternative, open an issue and it will be added.

Reference Documents

These documents are not hosted here! They are available on Library Genesis and at other locations.

Special Thanks