nRF52840 web server

Warning

Work in progress!

Writing a web server for the nRF52840 microcontroller to learn complex embedded systems programming and for fun. Built using FreeRTOS.

Clone with submodules:

git clone --recurse-submodules https://github.com/codetit4n/nrf52840-webserver

Commands:

# Build the firmware - Creates the firmware binary in the build/ directory
make
# Flash the firmware to the nRF52840
make flash
# Or, directly use nrfjprog
nrfjprog --program build/webserver.elf --chiperase --verify --reset
# Clean the build artifacts
make clean
# Monitor the serial output from the nRF52840 for debugging - 1M baud rate
minicom -D /dev/ttyACM0 -b 1000000

Work progress

Core drivers

• UARTE driver
• Ring-buffer logger
• Generic SPI master driver
  • FreeRTOS mutex-protected bus
  • Multi-device configuration
  • Blocking TX/RX with timeout
  • EasyDMA-safe buffer handling

Networking

• W5500 ioLibrary port
• Minimal networking module
  • Static IP configuration
  • Hardcoded HTTP response
• Re-enable W5500 alongside SD card
• Serve files from SD card over HTTP
• Add basic static-file support
  • HTML
  • CSS
  • JavaScript
  • MIME types
  • 404 responses
  • Basic path sanitization

SD card support

• SDHC/SDXC initialization in SPI mode

  • CMD0
  • CMD8
  • CMD55 + ACMD41
  • CMD58
  • SDHC/SDXC detection

• Read CSD using CMD9

  • Keep CS asserted for the complete data transaction
  • Wait for the 0xFE data token
  • Read 16-byte CSD
  • Read and discard CRC bytes

• Decode card block count from CSD v2

• Read a single 512-byte block using CMD17

  • Build the CMD17 argument from the requested block number
  • Send the block number in big-endian wire order
  • Wait for the 0xFE data token
  • Read 512 data bytes
  • Read and discard CRC bytes

• Verify block 0 against a PC-side sector dump

• Verify repeated raw reads are stable

• Verify a non-zero block against a PC-side sector dump

• Add CRC16 validation for received data blocks

• Create a clean read-only block-device API

  • Add sd_status_t
  • Return specific errors instead of -1
  • Add initialization-state tracking
  • Add block-range validation
  • Keep command helpers private to the SD implementation
  • Define command transaction ownership rules
  • Expose only sd_init() and sd_read_block() publicly

• Verify SD and W5500 operation on the shared SPI bus

Current limitation: only SDHC and SDXC cards are supported. SDSC and SD v1 cards are intentionally rejected.

Filesystem

• Integrate FatFs in read-only mode
• Implement FatFs disk I/O bridge
• Mount the SD card
• Open and read /index.html
• Print file contents over UART
• Add write support later, if needed

Web server

• Re-enable networking with SD card active
• Serve /index.html from SD
• Stream files in chunks instead of loading them fully into RAM
• Test repeated HTTP requests
• Add socket and SD timeout recovery

Documentation and release

• Architecture diagram
• Wiring table
• Build log
• README cleanup
• Demo video
• Tag a v1.0 release