8086 (was Re: more talking to the press.)

Am 16 Nov 2003 2:36 meinte Fred N. van Kempen: Aua. This hurts. There where several tests to distinguish the CPUs. Personaly I only used two of them in real products, but at one time I played around to produce a test as good as possible. Intel usualy documented the tests using the flag register, especialy for the later CPUs. it can prety much distinguisch getween 8086,286 and 386. To see if I have a 286, I set and the clear bit 12 to 15 - was 15 able to be set, it's a 286, while if I could set 12-14, but not 15, it's a 386. The other was to find if I had a 186 compatible instruction set (pusha, popa, bound, enter, leave, etc. oh, yes, and ins/outs, my favorites), which is true for everything except 8086/88 (even V20/30), which eas rather easy: Shift left for 32 Bits, and nothing if happens it's 186 compatible, otherwise it's a 8088/86. The other, less popular (since not recommended by Intel) technique was to code a pusha, which true 8088/86 interpreted as a Jump *+2 (or just ignoring the next two bytes), so one could now code here something like CLC, or check the stackpointers (don't forget the NOP). The last trick I re,member was the POP CS, which worked on a 8086/88, while generated an invalid opcode int on 186 and above. Now, to see if it's a V20/30 or not, one just goes ahead, sets the zero flag and does a multiplication (non zero result) - if Zero is still set, it's a V20 :) Another trick, at the same corner was the behaviour of AAD, which on intel realy uses the second byte as operand for the multiplication, while on V20/30, independent form the coding always 10 (0Ah) was used. To get the bus size, two methods are possible, either do self modifying code, and detect the legth of the prefetch que - the 8 Bit types (8088/188/V20) had 4 bytes, refilled when at least one Byte is empty, while the 16 Bit types had 6 Bytes and would be refiled only if two or more positions where empty. The other, less destructive was just to time a lodsw loop - if you had a sufficient good timer base, just go ahead and load huge data amounts into A (REP LODSW) and see what took you longer. But usualy it made no sense, since it didn't effect the operations you had at hand. Gruss H. -- VCF Europa 5.0 am 01./02. Mai 2004 in Muenchen http://www.vcfe.org/