E Ink Display Testing

E-Ink Display Chip Select Routing Test Plan

Overview

This document outlines the testing approach for the i.MX93 Jaguar E-Ink board's dual chip select routing system, based on hardware engineer feedback about level shifters and the L#R_SEL_DIS signal.

Hardware Architecture

Level Shifters (1.8V → 3.3V)

The display interface uses level shifters to convert i.MX93's 1.8V signals to 3.3V for the display:

• Autosensing Direction: Required for reading display registers (can be temperamental)
• Fixed Direction: More reliable but no register read capability
• Recommendation: Start with fixed direction buffers for initial testing

Chip Select Routing

• Display Controllers: Left (CS_M) and Right (CS_S)
• Single CS Line: Only one chip select from i.MX93 SPI controller
• Routing Control: L#R_SEL_DIS signal (GPIO2_IO16) routes CS:
  • LOW (0) → CS routes to left controller (CS_M)
  • HIGH (1) → CS routes to right controller (CS_S)

GPIO Mappings (i.MX93)

Function	GPIO	Number	Signal	Notes
Reset	GPIO2_IO14	526	RES_DIS#	Active-Low
Data/Command	GPIO2_IO15	527	D/C#_DIS	LO=Cmd, HI=Data
L/R Select	GPIO2_IO16	528	L#R_SEL_DIS	LO=Left, HI=Right
Busy Status	GPIO2_IO17	529	BUSY_DIS#	LO=Busy (Input)
Power Enable	GPIO2_IO11	523	POWER_EN	Display power

GPIO2 base address: 512 (e.g., GPIO2_IO16 = 512 + 16 = 528)

Changes Made

1. Device Tree Updates (imx93-jaguar-eink.dts)

Added Chip Select Routing Control Node

/* E-Ink Chip Select Routing Control */
eink_cs_routing: eink-cs-routing {
    compatible = "gpio-controller";
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_eink_cs_routing>;
    
    /* L#R_SEL_DIS GPIO control
     * LOW (0)  = Route CS to left controller (CS_M)
     * HIGH (1) = Route CS to right controller (CS_S)
     */
    lr-sel-gpio = <&gpio2 16 GPIO_ACTIVE_HIGH>; /* GPIO2_IO16 */
    
    /* Default to left controller for initial testing */
    lr-sel-default = <0>;
};

Added Pinctrl Configuration

/* E-Ink chip select routing control */
pinctrl_eink_cs_routing: eink_cs_routing_grp {
    fsl,pins = <
        MX93_PAD_GPIO_IO16__GPIO2_IO16    0x31e  /* L#R_SEL_DIS - Chip Select Routing Control */
    >;
};

2. Test Script (scripts/test-eink-cs-routing.sh)

Created comprehensive test script with:

• Individual Controller Testing: Test left and right controllers separately
• Level Shifter Validation: Test signal integrity on both routing paths
• Rapid Switching Test: Validate routing reliability
• GPIO Management: Proper export/unexport and cleanup

Usage Examples

# Set routing to left controller
./scripts/test-eink-cs-routing.sh left

# Set routing to right controller  
./scripts/test-eink-cs-routing.sh right

# Run comprehensive test
./scripts/test-eink-cs-routing.sh test

# Clean up GPIO exports
./scripts/test-eink-cs-routing.sh cleanup

Testing Procedure

Phase 1: Basic Connectivity

1. Power On: Verify display power regulator is working
2. GPIO Export: Ensure all GPIO pins can be exported and controlled
3. SPI Interface: Verify SPI communication is functional

Phase 2: Level Shifter Testing

1. Signal Integrity: Test GPIO signal transitions on both routing paths
2. Direction Detection: Verify autosensing vs fixed direction behavior
3. Timing Analysis: Check for signal delays or glitches

Phase 3: Controller Access Testing

1. Left Controller (CS_M):

   • Set L#R_SEL_DIS = LOW
   • Attempt SPI communication
   • Verify busy signal response

2. Right Controller (CS_S):

   • Set L#R_SEL_DIS = HIGH
   • Attempt SPI communication
   • Verify busy signal response

Phase 4: Rapid Switching

1. Routing Reliability: Test rapid switching between controllers
2. Level Shifter Stability: Ensure buffers handle direction changes
3. Signal Integrity: Verify no cross-talk or interference

Expected Results

Success Indicators

• ✅ Both controllers respond to SPI commands
• ✅ Busy signal changes appropriately for each controller
• ✅ No GPIO export/control errors
• ✅ Clean switching between left and right routing

Failure Indicators

• ❌ Only one controller responds → Check level shifter configuration
• ❌ Neither controller responds → Check SPI wiring and power
• ❌ GPIO control fails → Check device tree and pinctrl
• ❌ Signal integrity issues → May need autosensing buffers

Troubleshooting Guide

Issue: Only Left Controller Responds

• Cause: Fixed direction level shifters may not support right controller
• Solution: Switch to autosensing level shifters

Issue: Neither Controller Responds

• Cause: SPI wiring, power, or level shifter configuration
• Solution: Check power supply, SPI connections, and level shifter enable signals

Issue: Intermittent Response

• Cause: Level shifter timing or signal integrity
• Solution: Add delays, check signal quality, verify power supply stability

Issue: GPIO Control Fails

• Cause: Device tree configuration or pin conflicts
• Solution: Verify pinctrl settings and check for pin conflicts

Next Steps

1. Build and Deploy: Compile device tree changes and deploy to target
2. Run Tests: Execute test script to validate chip select routing
3. Level Shifter Optimization: Based on results, optimize level shifter configuration
4. Display Driver Integration: Once routing is validated, integrate with display driver
5. Performance Tuning: Optimize SPI timing and signal integrity

Files Modified

• meta-dynamicdevices-bsp/recipes-bsp/device-tree/lmp-device-tree/imx93-jaguar-eink.dts
• scripts/test-eink-cs-routing.sh (new)
• docs/EINK_CS_ROUTING_TEST_PLAN.md (this document)

Environment Variables

export TARGET_IP="192.168.1.100"      # Target board IP
export TARGET_USER="fio"               # Target username  
export SPI_DEVICE="/dev/spidev1.0"    # SPI device path

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Author: Dynamic Devices Ltd
Date: $(date)
License: Creative Commons Non Commercial
Copyright: Dynamic Devices Ltd 2025