Computer Science 237
Computer Organization

Williams College
Fall 2006

Lecture 08: More Assembly Programming
Date: September 25, 2006

Agenda

Announcements
Lab 2 is due; Lab 3 is out
Continuing Addressing Modes from Friday
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	"col",-(%sp)
    move.w	"row",-(%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)