Computer Science 237
Computer Organization

Williams College
Fall 2005

Lecture 8: More Assembly Programming
Date: September 26, 2005

Announcements

We hate cortland. We hate Apple. Try to stick with the FreeBSD systems this week.
Lab 2 due as soon as you can. Lab 3 out. We meet in TCL 312 this week.

Agenda

Last words on Addressing Modes
Another Assembly Translation Example
- Note that we must perform non-trivial compare.
```
	cmp.w	#160, %d4
   
```
  The arguments appear in the opposite order we'd expect in C.
  What it really does is computes a subtraction (d4-160) and sets the status bits, but throws away the result.
  Many instructions set status bits (not branches).
- Calling a WinDrawPixel involves involves an operating system call:
```
    move.w	"row",-(%sp)
    move.w  "col",-(%sp)
    oscall	WinDrawPixel
    add.l	#4,%sp
    
```
- Calling a user routine substitutes bsr.
- The modulus operator, here, is implemented by divu, unsigned division. Source is 16 bit, destination is 32 bit. Low 16 bits of result contains quotient; high 16 bit is remainder.

Examples

remainder (drawing a pattern on the palm display)