1. Memory The programmer’s model .text, .data .ktext, .kdata
user program (instruction memory) and data area
.ktext, .kdata
kernel program and data area
The computer’s model
instruction memory
user space 0-7fffffff, kernel space ffffffff
data memory

2. How can we tell User/Kernel apart?31 30 29 28 27 ? x x x
x…...
By looking at the address!
PC[31]
0, User program
1, Kernel program
data addr[31]
0, User data
1, Kernel data

3. Address Decoding So far; Instruction decoding Now address decoding 32PC
PC[31]
TAP
BOX
[31]

4. How to detect a kernel instruction
CPU model
How to detect a kernel instruction
kinst
CP0
MIPS PIPELINE 32
instruction
address
[31]
Instruction
Memory

5. How to detect kernel data access
CPU model
How to detect kernel data access
kdata
CP0
MIPS PIPELINE
data mem
address 32
[31]
Instruction
Memory

6. Address Mapping CP0 MIPS PIPELINE data mem address 32 32 data
8/16/32 bits
Address bus
Data bus

7. Address Mapping CP0 MIPS PIPELINE Control signals r/w, 8, 16, 32 bits
Address bus
Data bus
Control bus

8. Address Mapping Address bus Data bus Control bus 00……0 .. . 0fff…..f
10……0 .. .
1fff…..f
n0……0 .. .
nfff…..f ….
Mem 1
Mem 2
Mem n

9. Enable and REDUCED address
Address 0-7fffffff 31 30 29 28 27
[27:0] points out the REDUCED address in mem 1
mem 1 Enable

10. lw $t0 0($t1), $t1=0…0 Address bus Data bus Control bus
read=(ADDR[31..28]=0000)
and CTRL[READ]
word=CTRL[WORD] 32
address
decoder
read, word 28
data word
00……0 .. .
0fff…..f

11. lw $t0 0($t1), $t1=0…0 Address bus Data bus Control bus
CTRL[stall]=0 Until data ready 32
address
decoder
read, word 28
data word
00……0 .. .
0fff…..f

12. sb $t0 0($t1), $t1=0…0 Address bus Data bus Control bus
write=(ADDR[31..28]=0000)
and CTRL[WRITE]
byte=CTRL[BYTE] 32
address
decoder
write, byte 28
data word
00……0 .. .
0fff…..f

13. sw $t0 0($t1), $t1=0…1 Address bus Data bus Control bus
CTRL[ALIGNMENT]=(ADDR[31..28]=0000)
and (ADDR[0] or ADDR[1]) 32
address
decoder
Alignment Error!!!