a) Interrupts are used to invoke system activities that have to be performed on regular basis. Programmable interval timer (PIT) is using triggers that interrupt when it reaches the programmed count. Find out whether the frequency of Programmable Interval Timer (PIT) is fixed or not (for IBM PC compatibles)? Also give example how time tick generated through Programmable Interval Timer?
Programmable Interval Timer (PIT) frequency is fixed, however inside the chip there is a 16bit divisor that divides input frequency and the output is connected to the IRQ 0 line of the PIC. Programmable Interval Timer has a precise input frequency of 1.19318 MHz. To produce time ticks the default IRQ0 is generated 1193180/65536=18.2 times per second. This is known as PIT timer ticks. Here we have time interval of about 55ms between two timer ticks.
b) Write down the instructions those are used to inform the PIC about the end of an interrupt?
mov al, 0x20
out 0x20, al
c) PCB (Process Control Block) is a space where all registers of a task are stored. Describe how many bytes are needed to structure PCB and also explain different purposes of these bytes?
In assembly language we make the structure of PCB using 32 bytes. 28 bytes are used to store the 14 registers. And last 4 bytes are utilized to form a linked list that used to link the PCBs of different threads. So thread number is stored in these 4 bytes.
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