The Firefly HDMI-to-MIPI-CSI converter board converts an HDMI video and audio source into a MIPI-CSI camera stream for supported Rockchip SoCs, which is the complete opposite of the Olimex MIPI-HDMI adapter that converts MIPI DSI display signals to HDMI output.
Built around the Rockchip RK628D video bridge chip, the board supports HDMI 1.4/2.0 input with 8-bit and 10-bit video, RGB888 and YUV420 color formats, and resolutions up to 4K @ 60fps. On the output side, it provides a MIPI-CSI interface compliant with MIPI D-PHY v1.2, with video output in YUV422 color format, supporting resolutions up to 4K @ 30fps. Audio output is available through a 3.5 mm headphone jack and onboard pin headers, making the board suitable for HDMI capture, smart display, micro-projector, and embedded video conversion applications.
Firefly HDMI-to-MIPI-CSI board Specifications:
- Main Chip – Rockchip RK628D HDMI-to-MIPI CSI-2 converter
- Input
- HDMI 1.4 / HDMI 2.0 compliant
- 8-bit and 10-bit per component video
- Color formats: RGB888, YUV420
- Maximum input resolution – 3840 × 2160 @ 60 fps (YUV420)
- Output
- MIPI CSI-2 compliant (MIPI D-PHY v1.2)
- Output format – YUV422
- Interface – MIPI CSI-2 via FFC/FPC ribbon cable (pin count and pitch dependent on host board)
- Supported output resolutions
- 3840 × 2160 @ 30 fps
- 1920 × 1080 @ 60 fps
- 1280 × 720 @ 60 fps
- 720 × 480 @ 60 fps
- Audio
- 3.5 mm Line Out jack
- 3-pin 2.0 mm Line Out header
- 2-pin 1.25 mm Line Out header
- HDMI audio converted to analog line out
- Power – Powered via the CSI connector from the host board
- Dimensions – 43.5 × 30 mm
In the documentation page, Firefly mentions that the board is compatible with Rockchip solutions from the company, including RK3566 series (AIO-3566JD4, ROC-RK3566-PC), RK3568 series (AIO-3568J, ROC-RK3568-PC / SE), RK3588 series (ITX-3588J, AIO-3588Q), RK3588S series (AIO-3588SJD4, ROC-RK3588S-PC, AIO-3588SG), RK3576 series (ROC-RK3576-PC, AIO-3576Q), and RK3399 series (via CSI-30p to CSI-24p adapter on boards with CSI). Basically, any Rockchip board with a MIPI CSI connector, and you’ll find compatible Android and Linux images on the download page.
Hardware-wise, the RK628D adapter outputs MIPI-CSI, which is a standard physical interface on many SBCs and development boards. So in theory, if an SBC has an MIPI-CSI connector mapped according to Firefly standards, the hardware could receive the converted video. But there are two limitations:
- Radxa and other SBC families don’t all use the same CSI connector, lane configuration, or power/ground assignments, and there is no way to confirm that, as Firefly does not provide any schematic.
- Linux must have a compatible RK628D driver and correct device tree bindings for that specific board. Firefly publishes kernels and DTBs with RK628D support for their boards. Other SBC vendors (e.g., Radxa, Pine64, Orange Pi) may not ship RK628D support out of the box in their kernels. So, without kernel support, the hardware signals may arrive on CSI, but the kernel will likely not recognize the HDMI converter as a camera input.
While searching for more details about the RK628D HDMI-to-MIPI implementation, I came across a reference design by Taibai Jinxing (太白金星), who designed an RK628D-based HDMI-to-MIPI evaluation board using publicly available information and extracted Linux drivers. However, what he got was unstable display behavior caused by incorrect screen timing and insufficient LCD bias voltages, along with additional hardware limitations introduced by PCB-level compromises such as the crystal footprint mismatch. These issues show that without official RK628D documentation, a working HDMI-to-MIPI signal alone is not enough for reliable display operation. I also found a very interesting Reddit thread on the topic.
The Rockchip RK628D-based HDMI-to-MIPI-CSI board is available on AliExpress for $20.56. Alternatively, we previously noted the C790 HDMI to MIPI CSI HAT that does something similar for the Raspberry Pi boards, but there are others, such as the Waveshare HDMI to CSI adapter and the Geekworm X1301 adapter with HDMI loop.
Debashis Das is a technical content writer and embedded engineer with over five years of experience in the industry. With expertise in Embedded C, PCB Design, and SEO optimization, he effectively blends difficult technical topics with clear communication
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