Hi, I’m the Toradex AI Assistant.
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Based on your description, there are several critical issues that need to be addressed for your MIPI DSI display implementation on the Colibri iMX8X.
Signal Integrity Issues
Your suspicions about the interface board are well-founded. The Colibri iMX8X datasheet specifies strict DSI signal routing requirements that your interface board does not meet(1):
Critical Requirements Not Met:
- Trace Impedance: 90Ω ±15% differential; 50Ω ±15% single-ended(1)
- Max Intra-pair Skew: <1ps = 150μm(1)
- Max Trace Length Skew between clock and data lanes: <10ps = 1.5mm(1)
- Reference Plane: GND or PWR required(1)
- Minimum pair to pair spacing: >2x intra-pair spacing(1)
Your two-layer board without differential routing, length matching, or ground planes violates all these requirements. The in-phase signals you’re observing on your scope confirm poor signal integrity - MIPI DSI differential pairs should be 180° out of phase.
Hardware Specifications
The Colibri iMX8X MIPI DSI interface specifications(1):
- Max Frequency: 502.5MHz (1.05GT/s per data lane)
- Max Trace Length from Module Connector: 200mm
- Configuration: 1 load
- Data Lanes: Up to 4 lanes capable of up to 1.05GHz data
Display Interface Details
The Colibri iMX8X provides two MIPI/DSI interfaces through an FFC connector (X2)(1). The interface supports:
- Bidirectional communication (high-speed out, low power/speed in from display)
- MIPI D-PHY for physical layer
- Display resolution from 160x120 (QQVGA) to 1920x1200 (WUXGA) with 60Hz and 24bit(1)
Device Tree Customization
For MIPI DSI displays, you need proper device tree configuration(2). Device Tree Overlays can be used to modify the base device tree at runtime without rebuilding the entire system, which is particularly useful for display customization(2).
Recommendations
-
Immediate Action: Replace your interface board with a proper 4-layer PCB design that meets all the signal routing requirements specified in the datasheet(1)
-
Hardware Design: Ensure your new board includes:
- Controlled impedance routing (90Ω differential)
- Proper ground planes
- Length matching between differential pairs
- Minimal via usage in DSI traces
-
Software Verification: Your kernel module and device tree approach appears sound based on the community discussion patterns(3), but the hardware issues are preventing proper signal transmission.
The interface board you’ve shown cannot reliably support MIPI DSI signaling due to the high-speed nature of the interface (up to 1.05GT/s per lane). The signal integrity requirements are not optional - they’re necessary for the differential signaling to function correctly.
Best regards, Toradex AI Assistant.
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