Com1 uses which irq

The appropriate table entry must contain the segmented starting address of the function in the application program handling the interrupts. This function must end with a call to the IRET function.

This means, that a normal function inside your program cannot be used as an interrupt service routine. Refer to your own compiler manual for details. When an interrupt occurs, the software must check the IIR interrupt identification register to see which event caused the interrupt to occur.

See the programming examples for details. It honors new interrupts when the processor is busy processing another one, as long as the IRQ number of the new interrupt is lower than the currently occurring one.

Therefore, playing around with the interrupt numbers assigned to different devices in your computer can decrease or increase the maximum allowed speed of serial communications.

Be aware, that the system assumes most hardware to exist on a particular interrupt level, so look out what you are doing. Changing the interrupt level of hard-disks, floppy drives etc. An interrupt is not occurring, unless the PIC is told that it is allowed to pass an interrupt through.

The eight bits of the IMR mask register each control the behaviour of one interrupt line. If a bit is set to zero, the accompanying interrupt will be passed through to the processor.

Changing the IMR is easy. Then clear the bit and write the information back to the same location. Be sure to set the same bit when exiting the application. Otherwise, when new characters are received on the line when the application is not working anymore, the PIC will trigger the software interrupt routine on your machine which may lead to strange behaviour of the computer, including a complete crash.

The most important situation that must be taken care of is pressing the Ctrl-C button. In most applications, pressing this key will stop the program immediately, without restoring the IMR state, and even more important, the interrupt service routine address. The interrupt service routine is the function called when an interrupt occurs. This is a piece of software inside your application, but when the program is exited, other code will be present on the same memory location.

If the interrupt service routine starting address is not changed in the BIOS table, the BIOS will still perform a call to the same memory location when an interrupt occurs after the program has exited. Should I explain further? The PIC will prevent new interrupts of the same or lower priority, as long as the software has not finished processing the previous one. What Serial ports on a computer can be configured as?

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Has a human ever been mailed via the United States Postal Service? Still have questions? The ARM processor has a simple privilege model: all modes are privileged apart from User mode. Privilege is the ability to perform certain tasks that cannot be done from User mode.

For example, changing the operating mode is a privileged operation. These bits can be used for conditional execution of subsequent instructions. The processor comes out of reset in supervisor mode with unrestricted access to the processor and all of its resources. Each exception handling mode can access its own SPSR.