July 2008
Intermediate to advanced
544 pages
16h 52m
English
Content preview from Computers as Components, 2nd Edition
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
Start your free trial
66 CHAPTER 2 Instruction Sets
03 100
0 3 5
0 3 5
0 3 100
Data
Address
Memory
CPU
Instruction: LDR r0,[r1]
r1
r0
FIGURE 2.13
Register-indirect addressing in the ARM.
0 3 201
0 3 201 r15
Distance 5 0 3 101
SUB r1, r15, #&101
0 3 5
Memory
0 3 100 FOO
FIGURE 2.14
Computing an absolute address using the PC.
loads r0 from the address given by r1 r2, while
LDR r0,[r1, #4]
loads r0 from the address r1 4.
This begs the question of how we get an address into a register—we need to be
able to set a register to an arbitrary 32-bit value. In the ARM,the standard way to set
a register to an address is by performing arithmetic on the program counter, which
is stored in r15. By adding ...