VxWorks DosFS on FMQL45T900: eMMC Storage with VxBus and XBD

Table of Contents

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
#

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
#

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
#

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

Key Characteristics
#

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
#

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
#

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

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

Data Flow
#

Application issues file operation
iosLib routes request
DosFS translates to block operations
XBD handles caching and queuing
Driver executes hardware access

Core Structures
#

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
#

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

Initialization Steps
#

Create device:
```
blkXbdDevCreate()
```
Attach to XBD:
```
xbdAttach()
```
Register strategy functions:
- mmcStorageBlkRead()
- mmcStorageBlkWrite()

🔄 Read/Write Execution Flow
#

Read Path (CMD17)
#

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

Write Path (CMD24)
#

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

Key Properties
#

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

🔌 VxBus Integration and System Registration
#

The driver is registered through hwconf.c with:

Base address
Interrupt configuration

Required Components
#

INCLUDE_DOSFS
INCLUDE_XBD
INCLUDE_DEVICE_MANAGER
INCLUDE_FS_MONITOR

Verification
#

After boot:

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

✅ Validation and Testing
#

A full validation suite confirms functionality and stability.

Test Scenarios
#

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

Results
#

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
#

Strengths
#

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

Optimization Opportunities
#

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

🧠 Final Thoughts
#

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.

Reference: VxWorks DosFS on FMQL45T900: eMMC Storage with VxBus and XBD