Will OS request interrupt to device?

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Take UART as an example.

When UART received data, the UART device(chip) generates an interrupt, the SW interrupt handler will process this interrupt, ex: read data from HW buffer. This part is reasonable.

For TX case, will OS/driver generate an interrupt to the device (UART chip) to let UART chip know there are some data need to send out?


A typical way to handle UART input goes a bit further than you say:

When data has been received the UART generates a HW interrupt and the interrupt handler reads the data from UART and places it in a FIFO buffer, often a circular buffer.

At the higher level when the OS wants to receive data it looks at the input buffer to see if there is any data there.

This mechanism provides another layer of asynchronicity and it means that the input data flow control need only block the remote transmitter when the receiver's input buffer is (nearly) full.


One typical way to handle output is this:

The UART generates a HW interrupt when it is ready to transmit data. The interrupt handler will then look at the FIFO output buffer and place the first item in the queue in the UART's transmit register. Otherwise if there is no data waiting to be transmitted the interrupt status is cleared.

At the higher level when the OS wants to transmit data it places the item in the output buffer and ensures that the UART will generate a HW interrupt when it is ready to transmit, which may be straight away.

This means that the output data flow is only blocked when the output buffer is full.


Neither of these actually require a SW interrupt at the UART handling level. The SW interrupt is a convenient way for applications to communicate with the OS.

1.5. Basics of How Operating Systems Work, Hardware Interupts are generated by hardware devices to signal that they need A system call will set the CPU to kernel mode, as will traps and interrupts. How's the OS going to tell the difference between INT 9, Exception: Coprocessor segment overrun, and INT 9: IRQ 1? Well, it can ask the device whether there is really an interrupt for that device. But this is slow, and hackish, and not all devices are able to do this type of thing.


Device generate hardware interrupts not OS-es or drivers.

Generally communication hardware generate interrupts when:

  1. It has got some data
  2. It is ready to send data
  3. It is in error condition.
  4. It has ended the commucication (especially important for hardware with internal buffers like FIFOs)

If hardware uses DMA you may have another interrupts as well

  1. End of DMA transaction
  2. Half of the transaction
  3. DMA error

Interrupt, In digital computers, an interrupt is a response by the processor to an event that needs attention A software interrupt is requested by the processor itself upon executing particular a variety of purposes, such as requesting operating system services and interacting with device drivers (e.g., to read or write storage media). In Windows 8, the operating system does not support resource requests for more than 2048 interrupt messages per device function. In Windows 7 and Windows Vista, the operating system does not support resource requests for more than 910 interrupt messages per device function. If the device driver exceeds this limit, the device might fail to start.


To put things easier, here I check Linux 1.0 as the code base.

static void rs_stop(struct tty_struct *tty)
{
...
info->IER = UART_IER_MSI | UART_IER_RLSI | UART_IER_RDI; 
// you can see UART_IER_THRI is not here, the TX interrupt was disabled.
...
}

static void rs_start(struct tty_struct *tty)
{
    info->IER = (UART_IER_MSI | UART_IER_RLSI |
         UART_IER_THRI | UART_IER_RDI);
  // THRI is enabled here.
}

How do input devices and interrupts work?, Your keyboard is a very simple input device; simple because it generates small there will be an interrupt handler, a part of the operating system that stashes Earlier, I referred to a disk controller using the bus to signal that a disk request  The device wold cause an interrupt when the request is completed. That what is meant by an "I/O Device Request" in your table. The confusion is that interrupts, faults and traps are all handled the same way by the operating system through the dispatch table. And, as I said, in Intel land they call both traps and interrupts "Interrupts".


Interrupts, When a device requests an interrupts, the value of INTR is the logical OR of the requests Processor is in supervised mode only while executing OS routines. 1. Device asserts level triggered interrupt 2. PIC tells CPU that there is an interrupt 3. CPU acknowledges and waits for PIC to send interrupt vector 4. However, device de-asserts interrupt. What does the PIC do? This is a spurious interrupt To prevent this, PIC sends a fake vector number called the spurious IRQ. This is the lowest priority


10. Interrupt Handling, If a module requests an IRQ at initialization, it prevents any other driver from using the interrupt, even if the device holding it is never used. Requesting the  The interrupt specification is information the system uses to bind a device interrupt source with a specific device interrupt handler. The specification describes the information provided by the hardware to the system when making an interrupt request.


On a PC, what is an Interrupt Request number?, An Interrupt Request is a signal from a hardware device on your use the same IRQ number, and the operating system or motherboard has no  Interrupt handlers. An interrupt handler, also known as an interrupt service routine or ISR, is a piece of software or more specifically a callback function in an operating system or more specifically in a device driver, whose execution is triggered by the reception of an interrupt.