Module 4: Device Manager

Handles Terminal I/O and Disk operations (Load and Store).

Disk Store¶

Description : Stores the contents of the page into the disk block. A valid PID as input is assumed.

Acquire the lock on the disk device by calling the Acquire_Disk() function
in the Resource Manager module;

Set the LOAD/STORE BIT, PAGE NUMBER and BLOCK NUMBER in the Disk Status Table.

Use the store statement to store the memory page to disk;

Set the state as (WAIT_DISK, - );

Call the switch_context() function from the Scheduler Module.

return;

Called by Shutdown, Buffer Read and Buffer Write.

Disk Load¶

Description : Loads the contents of the disk block to the page. A valid PID as input is assumed.

Acquire the lock on the disk device by calling the Acquire_Disk() function
in the Resource Manager module;

Reset the LOAD/STORE BIT, set PAGE NUMBER and BLOCK NUMBER in the Disk Status Table.

Use the load statement to load the disk block to memory;

Set the state as (WAIT_DISK, - );

Call the switch_context() function from the Scheduler Module.

return;

Called by the Buffer Read, Buffer Write functions, exec system call (to load the first code page) and the exception handler (demand paging).

Note: The bootstrap code must use loadi statement and not this function.

Terminal Write¶

Description : Reads a word from the Memory address provided to the terminal. Assumes a valid PID is given.

    Acquire the lock on the terminal device by calling the Acquire_Terminal() function
    in the Resource Manager module;

    Use the print statement to print the contents of the word
    to the terminal;

    Release the lock on the terminal device by calling the Release_Terminal() function
    in the Resource Manager module;

    return;

Called by the Write system call.

Terminal Read¶

Description : Reads a word from the terminal and stores it to the memory address provided. Assumes a valid PID is given.

Acquire the lock on the disk device by calling the Acquire_Terminal() function
in the Resource Manager module;

Use the read statement to read the word from the terminal;

Set the state as (WAIT_TERMINAL, - );

Call the switch_context() function from the Scheduler Module.

Copy the word from the Input Buffer of the Process Table of the process corresponding to PID
to the memory address provided.

return;

Called by the Read system call.