Lecture 12

Memory-Mapped I/O (MMIO)

Lecture

Slides (PDF, PPTX).

Outline

• I/O devices
• Direct memory access (DMA)
• Memory-mapped I/O (MMIO)
• Drivers
• RARS MMIO device emulators

Examples

• digit_lab1.s
• digit_lab2.s
• digit_lab3.s
• bitmap_display.s
• mmio_poll.s
• mmio_interrupt.s

Workshop

1. Input a floating-point number, round it to one digit to the left of decimal point (e.g. 3.5) and display it in the Digital Sim Lab display. User digit_lab1.s as a starting program.

Homework

Solve the following tasks:

1. Modify the digit_lab2.s program to display keys pressed in the hexadecimal keyword in the digital display (as decimal values, e.g. F == 15). Use the workshop task as a basis.

2. Write a program (based on digit_lab2.s) that inputs an integer value X (with the ReadInt system call) and then uses Digital Sim Lab to enter 32-bit integers (8 hexadecimal digits) Y. It repeats entering integers until the entered Y is not equal to X. Then it prints FOUND and exits. If Y equals 0 the program must print STOPPED and exit.

3. Write a program that draws a square with size 64×64 dots in the middle of Bitmap Display (see the Tools menu of RARS) with size 128×128 dots. The color and the thickness of lines in dots is specified by the user (use the ReadInt system call). See bitmap_display.s as an example.

4. Bonus task (2 bonus points). EightSectors

Commit the programs to your private GitHub account. Place them into the folder ca/lab08.

References

• Memory-mapped I/O (Wikipedia).
• Direct memory access (Wikipedia).