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inode in memory.
Added a jump instruction in front of the multiboot header so that the
kernel may be run as a binary image. The jump instruction will skip over
the multiboot header to the beginning of the kernel's startup procedure
in kboot.
Moved the call to initialize the timer to earlier in the boot sequence.
This is to allow for some drivers that may require it's functionality
during the startup to function properly.
Added functionality for the 'fast-gate' to the enable_a20 subroutine.
Now, if the keyboard controller method fails when enabling the gate, an
attempt is made to enable the A20 gate using the PS/2's fast-gate
interface. If this also fails, the kernel will panic.
Implemented TTY output for the console. The console is now TTY device 0
(the default for new userspace programs).
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Removed the rsputs() function in favour of calls to tty_write().
Corrected a bug in the serial driver and TTY subsystem where a full
buffer wouldn't be detected. This was caused by a missing set of
brackets on several operations involving the modulus operator.
Added the ability for the serial driver to automatically take data from
the TTY device's write buffer and push it to the serial port. This can
happen in one of two ways; 1) the TTY subsystem notifies the serial
driver of new data by calling the write() function pointer in the
tty_struct or, 2) the serial port issues an interrupt signalling that it
has finished sending data prompting the driver to check the buffers for
any more pending data.
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the project.
Added the system call 'sys_panic' as well as the corresponding library
function panic() whose prototype is defined in unistd.h. This is to
allow userspace programs to deliberately crash the kernel for the
purpose of debugging.
Added the element 'write' as a function pointer in the tty_struct
structure. The purpose of this function pointer is to provide a means
for the TTY subsystem to notify the device driver of any newly added
data to the write queue.
Added the tty_write() function to the TTY subsystem. This function will
copy data provided by the user into the specified TTY device's write
queue, blocking if the queue's buffer is full. tty_write() will then
call the driver's write() function to notify it of new data.
Added the rsint_tx() function to the serial driver to handle transmit
interrupts by re-supplying the UART's transmit FIFO.
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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.
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