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