unix - Homebrew UNIX operating system

Age	Commit message (Collapse)	Author
2018-08-22	Added the header file limits.h which contains one definition for	Jake Mannens
	SSIZE_MAX which is needed to limit the number of bytes read() will transfer. Laid the foundation for a TTY subsystem. This works by taking the previously used buffer and r/w pointers concept and implements it as a 'tty_queue' struct. The struct 'tty_struct' is used to represent a TTY device. This struct currently contains three elements; a read queue for data flowing from the device to the user, a write queue for data flowing from the user to the device and a function pointer to an init function. The latter element will reduce complexity by allowing the TTY subsystem to initialize each TTY device driver (when it's ready), rather than each driver having to be initialized during bootup. Each TTY device is implemented as a pointer to a tty_struct. The structures are defined separately by each driver as well as tracked and maintained by pointers in the table 'ttys' in tty.c. Modified the RS232 serial driver to make use of the new TTY subsystem for transferring data to the user. Currently, write calls are still handled manually through the rsputs() function though this will change in future. Modified the read() system call to direct read calls to the TTY subsystem which will further direct the call to the appropriate TTY device driver. The serial driver's interrupt routine now uses the wake_up() function to wake processes blocking for serial data. This is to ensure the scheduler is notified of the wakeup. This function is the preferred method for waking processes since accessing the task state field directly may not be possible in the future and is discouraged. The reason for this is that the scheduler's behaviour may change to require being notified of task wakeup events in the future.
2018-08-06	Defined ssize_t in unistd.h.	Jake Mannens
	Added the _syscall2 macro to unistd.h to facilitate system calls that require two arguments to be passed. Modified the ATA driver to simply abort initialisation if a drive is not found, or cannot be configured. This will allow the kernel to function on a diskless system without invoking panic() unnecessarily. Added the functions irq_enable() and irq_disable() to asm/interrupt.h to make it easier for C code to mask and unmask IRQ's on each PIC. Moved the declaration for rsputs() from kernel/con.h to the new kernel/serial.h file since this is a function provided by the serial driver. Implemented a basic I/O input framework. This involves the new system call sys_read, which takes an I/O read request and directs it to the appropriate kernel handler function depending on the calling process' ctty value. This mechanism is identical to the sys_puts system call. Added the rsread() function to service sys_read calls from processes whose ctty value is equal to 1. This function will continually copy data from the serial buffer to the location specified. If there is not a sufficient amount of new data in the buffer to satisfy the request, the process is put into the TSTATE_UNINTERRUPTIBLE state and the scheduler is called to switch tasks. Prior to calling the scheduler, the function will set the waiting_task pointer to the calling process. This pointer will later be used by the interrupt handler to wake the process when new data arrives. Added an interrupt handler to service the IRQ4 (UART) interrupt. This subroutine is a stub which will save the machine's state then transfer control to rs_handler() in serial.c which will read bytes from the serial port and place them in a buffer. Before returning, rs_handler() checks the waiting_task pointer to see if a task is waiting for the newly received data and if so, it sets the task's state to TSTATE_RUNNING before resetting the pointer to NULL and returning. Ideally, the scheduler should be invoked at this point to select another task but since our basic round-robin scheduler currently has no concept of task priorities (and for the sake of simplicity), we will avoid invoking the scheduler in response to interrupts for now.