I/O Devices

Assignment Content

Question 1

In virtually all systems that include DMA modules, DMA to main memory is given higher priority than CPU access to main memory. Why?

Question 2

When a device interrupt occurs, how does the processor determine which device issued the interrupt?

Question 3

A system is based on an 8-bit microprocessor and has two I/O devices.

The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.
How many 8-bit I/O control module registers do we need for status reading and control of each device?
***Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 4
A system is based on an 8-bit microprocessor and has two I/O devices.
The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.
What is the total number of needed control module registers given that the first device is an output-only device?
***Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 5
A system is based on an 8-bit microprocessor and has two I/O devices.
The I/O con- trollers for this system use separate control and status registers.
Both devices handle data on a 1-byte-at-a-time basis.
The first device has two status lines and three control lines.
The second device has three status lines and four control lines.
How many distinct addresses are needed to control the two devices?
***Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 6
Consider a microprocessor that has a block I/O transfer instruction such as that found on the Z8000.
Following its first execution, such an instruction takes five clock cycles to re-execute.
However, if we employ a nonblocking I/O instruction, it takes a total of 20 clock cycles for fetching and execution.
Calculate the increase in speed with the block I/O instruction when transferring blocks of 128 bytes.
**Explain your reasoning and show your mathematical calculations on how you derived your answer
Question 7
What is the difference between memory-mapped I/O and isolated I/O?

KEY TAKEAWAYS BEFORE ATTEMPTING THIS ASSIGNMENT

When a device interrupt occurs, how does the processor determine which device issued the interrupt?

Introduction

When a device interrupt occurs is one of the most common questions asked by developers who are working with the Microsoft Platform. The question has been discussed in detail many times over at MSDN and Stack overflow, so we won’t reinvent the wheel here. Here’s a typical scenario where you might receive an interrupt after you’ve already fired off an IRP to your device driver: Suppose you have just created an object in Win32k. You then call CreateWindowEx() with dwStyle = SDB_CURSOR and dwWindowStyle = WS_OVERLAPPEDWINDOW. That code will trigger an IRP_MN_CREATE request to the device driver for your window, as shown below in Figure 1 (this is with an empty string passed to DbgPrint()).

When a device interrupt occurs is one of the most common questions asked by developers who are working with the Microsoft Platform. The question has been discussed in detail many times over at MSDN and Stackoverflow, so we won’t reinvent the wheel here.

To help you better understand how your code is called when an interrupt occurs, let’s take a look at some example scenarios and then think about what steps should be taken next when developing drivers for Windows 10 devices.

Here’s a typical scenario where you might receive an interrupt after you’ve already fired off an IRP to your device driver.

An example of this is CreateWindowEx() with dwStyle = SDB_CURSOR and dwWindowStyle = WS_OVERLAPPEDWINDOW. If you call CreateWindowEx(), Windows will check to see if the caller has already issued an IRP. If they have, then they aren’t allowed to do another one until all pending IRPs have completed successfully or have failed due to an exception (e.g., BadDevice).

If it’s not possible for your application developer to know whether or not there are any outstanding IRPs (for example, because he doesn’t keep track of these things), then he may need help from the operating system in order for his application to function properly–in this case, that means that he should use GetDllHandle() instead when calling CreateWindowEx().

Suppose you have just created an object in Win32k. You then call CreateWindowEx() with dwStyle = SDB_CURSOR and dwWindowStyle = WS_OVERLAPPEDWINDOW.

To understand how this works, let’s go through a simple example. Suppose you have just created an object in Win32k. You then call CreateWindowEx() with dwStyle = SDB_CURSOR and dwWindowStyle = WS_OVERLAPPEDWINDOW.

The first thing that happens is that your application calls the SystemParametersInfo() function to get some information about its environment. This function returns a pointer to an array of structs containing various parameters for accessing hardware resources on your system (for example, registry keys).

In our case, we want to know if there are any other windows open besides ours; so we use this API call:

The code above will trigger an IRP_MN_CREATE request to the device driver for your window, as shown below in Figure 1 (this is with an empty string passed to DbgPrint()).

The kernel then creates a window object and returns it back to Win32k, which then deposits it in your process’ address space.

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