marcl@3comvax.UUCP (Marc Lavine) (09/20/86)
I want a certain program to be able to distinguish between an 80386
and an 80286. I could try using self-modifying code (to test the size
of the prefetch queue, but I was wondering if there might be simpler
methods. This test will be done on a system running MS-DOS, so I
guess that means the '386 will be in real mode. Any help would be
appreciated.
--
Marc Lavine
uucp: ...{ ihnp4 | hplabs | glacier }!oliveb!3comvax!marclclif@intelca.UUCP (Clif Purkiser) (09/23/86)
> I want a certain program to be able to distinguish between an 80386 > and an 80286. I could try using self-modifying code (to test the size > of the prefetch queue, but I was wondering if there might be simpler > methods. This test will be done on a system running MS-DOS, so I > guess that means the '386 will be in real mode. Any help would be > appreciated. > -- > Marc Lavine > uucp: ...{ ihnp4 | hplabs | glacier }!oliveb!3comvax!marcl Sorry to post this to the net. But I got a message from the mail deamon. Hopefully it will be useful to the network. The follow article is from a technical note I wrote on identifying Intel microprocessors. Note this test only works in Real Mode. IDENTIFYING INTEL MICROPROCESSORS Many companies will soon have systems based on three generations of Intel microprocessor (8086/88, 80286, and the 80386.) It is often important that the same software be able to run on all three types of computers. Rather than writting all of the software to use only the 8086 instructions, many independent software vendors (ISVs) and computer companies are writting software to take advantage of the new features of the 80286 and/or 80386. The general method for doing this is to test what type of processor the computer contains and then branch to processor specific routines. This approach enables the same software to run on any Intel processor while still allowing the greater addressing capabilities and new instructions of the 80286/80386 to be used. There are several different methods of determining in software the processor type. One approach is to try the new instructions available on each processor and see if they cause an illegal opcode exception. The only disadvantage with this approach is that it requires access to the illegal opcode interrupt handler (exception 6) in order to determine the processor type. The April 86 issue of PC Tech contains an article by Bob Smith which documents most of the non-transparent differences between the 8088, 8086, 80186, and 80286. Mr. Smith's article seems to be accurate but many of his methods for determining the processor type seem to be unnecessarily complicated. More importantly Intel can not commit to support all of his tests in future 8086 core proliforation products since many of his tests use old errata. Luckily a much simpler method of determining the processors type exists. My test for determining between 8086, 80286, and 80386 involves taking advantage of differences in the flag register between the processors. Future versions of this processors will retain the same flag settings. Differentiating the 8086 from the 80286-80386 Bit 15 of the flag register is undefined on all three processors. In fact the bit is a 1 on the 8086/88 and 80186/88 and a 0 on the 80286 and 80386. Differentiating the 80286 from 80386 Bit 14 of the flag register on the 80286 and the 80386 is the Nested Task Flag. Bits 12-13 of the flag register is the I/O privilege level (IOPL). Since these bits are only used for Protected Mode software their values are undefined in Real Mode. In reality the bits are 0 after reset. None of these bits can be set on a 80286 in Real Mode. On a 386 all three of these bits can be set in Real Mode (although they have no effect). Differentiating the 8086 from the 80186 Unlike the other processors the 8086 and 80186 have no differences in the settings of the flag bits. However there is a difference between the processors in the operation of the shift instructions. The shift by a count instruciton on the 8086 used all 8 bits in the CL register to shift by. On the 80186 only the lower 5 bits are used as a count to the shift instruction. Thus 80186/286/386 use CL MOD 32 for the shift count. Therefore a shift of 33 is the same as a shift by 1 for the 80186/286/386 and on the 8086/88 it causes an all zero result. Future processors. The 80386 contains a processor type and a stepping identifier in the general purpose registers immediately after reset. Initialization software is strongly encouraged to check this registers and store the processor type in an area available to application programs. The 486 and future versions of the 386 will also contain this stepping identifier. Identifying Intel Processors. The attached code sequence returns the processor type in the AX register. It should be distributed to any customers and Independent Software vendors who could use it. proc_type proc near ; ; Returns the processor type in the AX ; pushf ; Save FLAG registers xor ax,ax ; Clear AX and push onto the stack. push ax popf ; Pop a zero into FLAGs register pushf ; Attempt to set bit 12-15 to a zero pop ax ; Recover FLAG word and ax, 0f000h ; If Bits 12-15 are then the processor cmp ax, 0f000h ; is an 8018x or an 808x jz is_0_1 mov ax, 07000h ; Try to set FLAG bits 12-14 (NT, IOPL) push ax popf ; put 07000H into flags pushf pop ax and ax,07000h ; if bits 12-14 are cleared then the jz is_80286 ; processor is an 286 is_80386: ; Else it is a 386 mov ax, 386h ; return 386 in AX jmp done is_80286: mov ax, 286h ; return 286 in AX jmp done is_0_1: ;It is a 8086 or a 80186 push cx ; Save CX the only other register used mov ax, 0ffffh ; Set AX to all 1s mov cl, 33 ; will shift it 33 times if it is an ; 808x or 1 time if it is an 8018x shl ax, cl ; if we shift 33 times all bits are jnz is_80186 ; zero. If any bits are on it's an 18x is_8086: ; Else we have an 8086 mov ax,86h ; Return 86 in AX pop cx ; restore cx jmp done is_80186: mov ax, 186h ; Return 186 in AX pop cx done: popf ; Recover original FLAG register ret proc_type endp -- Clif Purkiser, Intel, Santa Clara, Ca. {pur-ee,hplabs,amd,scgvaxd,dual,idi,omsvax}!intelca!clif I guess I better put back the old disclaimer line. These views are my own property. However anyone who wants them can have them.