What is System Programming?

1
Lecture 20
2
Determining the Processor Type

• Flags register test to identify 8086

12
15
Unused in 8086
Pushing or Pop the flags register will set these
4-bits in 8086.
3
Determining the Processor Type

• mov AX, 0
• push AX
• popf
• pushf
• pop AX
• Test the bits 15 12 of AX if all set, the
• processor is 8086 else higher processor.

4
Determining the Processor Type

• Flags test for 80286
• mov AX, 7000H
• push AX
• popf
• pushf
• pop AX
• If the bits 14 12 are cleared the
• processor is 286 only.

5
Alignment Test ( If Not 286)
18

Eflags
Alignment Check
Alignment Check mov dword ptr 12, EDX
6
Alignment Test

• pushfd
• pop eax
• mov ecx, eax
• mov dword ptr 13, EDX
• pushfd
• pop eax

7
CPUID Test

• 486 will pass the alignment test.
• To distinguish 486 with Pentium CPUID Test is
  used.

8
CPUID Test
21

Eflags

• If a program can set and also clear bit 21 of
  Eflags, then processor supports CPUID
  instructions.
• Set bit 21 of Eflags and read value of Eflags and
  store it.
• Clear bit 21 of Eflags, read the value of Eflags.
• Compare both the value if bit 21 has changed the
  CPUID instruction is available.

9
CPUID Instruction

• Before After the execution of Instruction
• EAX 0 EAX 1
• EBX EDX ECX
• EBX Genu
• EDX ineI
• ECX ntel
• EAX 1 EAX (bit 3 0) Stepping ID
• EAX (bit 7 4) Model
• EAX (bit 11 8) Family
• EAX (bit 13 12) Type
• EAX (bit 14 31) Reserved

10
Coprocessor Control Word
7
1 1
Interrupt enable flag
11 after initialization signifies extended
precision operation
11
Coprocessor Status Word
10
14
8
9
C0
C3
C1
C3
C3 C2 C0 0 0
0 st gt operand 0 0
1 st lt operand 1 0
0 st operand
12
To Check Coprocessor is Present

• Initialize
• Read Hi Byte of Control register.
• If value in Hi Byte is 3, then coprocessor is
  available, otherwise its absent.

13
Check for 8087 Coprocessor

• IEM can be set in 8087.
• IEM cannot be set in 80287, 80837 as they use
  exception to inform the software about any
  invalid instruction.
• If an attempt to set this bit fail then it
  implies, its not a 8087 coprocessor FDISI.

14
Distinguish between 80287 80387

• 80387 only allows to reverse the sign of
  infinity.
• Perform a division by zero.
• If the sign of result can be reversed then the
  coprocessor is 80387.

15

void PrintConfig( void )


union REGS Register BYTE
AT
clrscr() AT (peekb(0xF000, 0xFFFE) 0xFC)
printf("CONFIGC
- (c) 1987, 92 by Michael Tischer\n")
printf("Your PC Configuration \n")
printf("------------------
----------------------------\n") printf("PC
type ")
switch( peekb(0xF000, 0xFFFE) )

case 0xFF printf("PC\n")
break
case 0xFE
printf("XT\n")
break
default printf("AT or higher\n")
break


16
printf("Conventional RAM ")
int86(0x12, Register,
Register) printf("d K\n",Register.x.ax)
if ( AT )
Register.h.ah 0x88 int86(0x15,
Register, Register)
printf("Additional RAM d K over 1
megabyte\n", Register.x.ax)

int86(0x11, Register, Register)
printf("Default video mode ")
printf("Disk drives d\n",
(Register.x.ax gtgt 6 3) 1) printf("Serial
interfaces d\n", Register.x.ax gtgt 9
0x03) printf("Parallel interfaces
d\n\n", Register.x.ax gtgt 14)




void main()


PrintConfig()