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TinyHFS

Hierarchical file system implemented for the Orbit Booster Pack in conjunction with the TM4C123GXL. The system has a UNIX-like command line UI accessed through the Serial (UART) interface.

Hardware Components

  • 32KB 24LC256 EEPROM integrated into the Orbit Booster Pack
  • Serial (UART) interface

Files

  • Files can be of variable length

  • Files are plain text

  • Files are stored at the end of the EEPROM

  • Every file contains a header (not visible to user) with the following attributes (in order as stored in the EEPROM):

    • File name
    • File start address
    • File end address
    • Parent folder start address

  • Each of the above attributes occupy 2 bytes (a short int) in the EEPROM

  • The name of the file is restricted to 10 characters, but can be modified

  • The total size of a file header is [10 + (2 * 3)] bytes = 16 bytes

Folders

  • Folders are modeled as headers within the EEPROM

  • Folders are found at the start of the EEPROM

  • The Hierarchy is modeled as top-down and represented as follows: (E:/folder1/folder2/../file1.txt), where E:/ represents the root directory

  • The root folder's address is 32,767 - it is a hypothetical folder since it is outside of the folder partition

  • Every folder contains the following attributes (in order as stored in the EEPROM):

    • Folder name
    • Folder start address
    • Parent folder start address

  • Each of the above attributes occupy 2 bytes (a short int) in the EEPROM

  • The name of the folder is restricted to 10 characters, but can be modified

  • The total size of a folder is [10 + (2 * 2)] = 14 bytes

Partitions

  • The EEPROM is partitioned to separate the file headers, folders and files for efficiency and ease of access.
  • 27,768 bytes are allocated to the file partition
  • 3,998 bytes are allocated to the file header partition
  • 1,000 bytes are allocated to the folder partition
  • This will allow us to store a maximum of 71 folders and 249 file headers in all cases
  • If on average a file is composed of 300 bytes, the system can store 92 files
  • The number of files can never exceed the number of file headers (the upper limit on file headers applies to files as well)
  • The first byte of EEPROM is used to store the number of files in the system for utility - this byte is accessed as a state variable, and is referred to as the 'file count byte'
  • The system will be represented in memory with the following addresses:
File Count Byte ---- Folders ---- --------------- Files --------------- --------- File Headers --------- 
    0       | 1 --------- 1,000 | 1,001 ------------------------ 28,768 | 28,769 ------------------ 32,766

Commands

  • The commands that have been implemented successfully to date are the following:

    • file [filename] -> Creates new text file with the given file name - if file already exists, then throw an error
    • read [filename] -> Displays the contents of the specified file
    • delfile [filename] -> Deletes the specified file
    • rnfile [filename] -> Renames the specified file

    • mkdir [foldername] -> Creates new folder with the given folder name - if the folder already exists within the current directory, then throw an error
    • in [foldername] -> Steps into the specified folder, down a level
    • out -> Steps up to the parent folder
    • delfol [foldername] -> Deletes the specified folder
    • rnfol [foldername] -> Renames the specified folder

    • ls -> Displays the current folder's contents
    • pwd -> Displays the current working directory
    • omem -> Organizes the memory by removing gaps between adjacent files
    • help -> Displays the list of commands
    • format -> Clears the entire file system

UI

  • The UI of the system is operated directly through the input of the Serial terminal
  • Users enter their commands delimited with a newline character and send them via Serial
  • The system parses the command and sends the output to the Serial terminal
  • Warnings and errors are provided as feedback (eg. if the user attempts to write a file that exceeds the available space)

Authors

Ben Upenieks and Chaitanya Varier