VxWorks DosFS on FMQL45T900: eMMC Storage with VxBus and XBD

VxWorks DosFS on FMQL45T900: eMMC Storage with VxBus and XBD

Reducing reliance on external silicon while maintaining high reliability is a key goal in modern embedded systems. This article presents a production-grade eMMC file system implementation on the FMQL45T900 SoC using VxWorks, combining a VxBus-based block device driver, the XBD caching layer, and the DosFS file system.

The result is a modular, high-performance storage stack with full read/write capability and strong reusability.

🔍 Platform Context: FMQL45T900 and VxWorks

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The FMQL45T900 is a programmable SoC integrating:

• Quad-core ARM Cortex-A7
• FPGA fabric for custom logic
• Rich peripheral interfaces
• SMP support

With an available VxWorks BSP, it provides a solid foundation for building reliable storage subsystems.

VxWorks Storage Stack Overview

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VxWorks organizes storage into layered components:

• Application Layer

  • POSIX APIs (open, read, write, close)

• File System Layer

  • DosFS (FAT16/FAT32 support)

• Block Layer

  • XBD (Extended Block Device)

• Driver Layer

  • VxBus-based eMMC driver

This separation ensures clean abstraction and portability.

🛠️ eMMC Hardware Interface and Configuration

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The system uses an eMMC 5.1 device configured in SDR mode.

Key Characteristics

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• Bus Width: 4-bit
• Clock: 25 MHz
• Signals:
  • EMMC_CLK, EMMC_CMD, EMMC_D[0:3]
• Power Domains:
  • VCC (NAND array)
  • VCCQ (controller I/O)

Device Tree Configuration

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mmc0: dwmmc@e0043000 {
    compatible = "fmsh,psoc-dw-mshc";
    reg = <0xe0043000 0x1000>;
    clocks = <&clkc NCLK_AHB_SDIO0>, <&clkc NCLK_SDIO0>;
    clock-names = "biu", "ciu";
    bus-width = <4>;
    cap-mmc-highspeed;
    status = "okay";
};

This enables the controller and binds it to the VxWorks driver infrastructure.

📐 Storage Architecture: DosFS + XBD + Driver

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At system initialization, the storage stack is brought online through:

• usrDosfsInit()
• dosFsCacheLibInit()
• xbdInit()
• fsMonitorInit()

Data Flow

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1. Application issues file operation
2. iosLib routes request
3. DosFS translates to block operations
4. XBD handles caching and queuing
5. Driver executes hardware access

Core Structures

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struct xbd {
    struct device xbd_dev;
    struct xbd_funcs *xbd_funcs;
    unsigned xbd_blocksize;
    sector_t xbd_nblocks;
};

struct bio {
    device_t bio_dev;
    sector_t bio_blkno;
    unsigned bio_bcount;
    void *bio_data;
    unsigned bio_resid;
};

XBD abstracts block devices and optimizes I/O throughput.

🔧 Block Device Driver Design

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The eMMC driver follows VxWorks block device conventions and integrates via VxBus.

Initialization Steps

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1. Create device:

   blkXbdDevCreate()
   

2. Attach to XBD:

   xbdAttach()
   

3. Register strategy functions:

   • mmcStorageBlkRead()
   • mmcStorageBlkWrite()

🔄 Read/Write Execution Flow

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Read Path (CMD17)

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• Configure block length (512 bytes)
• Issue single-block read
• Receive data + CRC
• Send stop command (CMD12)
• Validate CRC16

Write Path (CMD24)

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• Configure block length
• Issue write command
• Transmit data + CRC
• Wait for DATA0 busy release
• Send CMD12

Key Properties

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• Sector size: 512 bytes
• FAT compatibility: ensured
• Data integrity: CRC validation

🔌 VxBus Integration and System Registration

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The driver is registered through hwconf.c with:

• Base address
• Interrupt configuration

Required Components

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• INCLUDE_DOSFS
• INCLUDE_XBD
• INCLUDE_DEVICE_MANAGER
• INCLUDE_FS_MONITOR

Verification

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After boot:

• vxBusShow → confirms device binding
• devs → shows /mmc0:0

✅ Validation and Testing

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A full validation suite confirms functionality and stability.

Test Scenarios

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• FTP file upload to mounted volume
• Application-level read() verification
• Direct driver read comparison
• Write tests with incremental patterns

Results

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• Data consistency across all layers
• Stable repeated read/write cycles
• No observed corruption or mismatch

This validates correctness, robustness, and performance.

🚀 Performance and Reliability Considerations

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Strengths

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• Modular architecture
• Efficient caching via XBD
• Low-latency block access
• Clean driver abstraction

Optimization Opportunities

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• HS400 mode enablement
• DMA tuning for higher throughput
• Advanced wear-leveling strategies

🧠 Final Thoughts

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This implementation demonstrates a complete and production-ready storage stack for VxWorks on FMQL45T900. By combining VxBus, XBD, and DosFS, it achieves a balance of performance, modularity, and maintainability.

The design serves as a strong reference for:

• Embedded storage system development
• BSP-level driver integration
• High-reliability industrial platforms

Future enhancements can extend performance and adaptability, but the current solution already provides a solid, deployable foundation for modern embedded systems.