First post, by vladstamate
- Rank
- Oldbie
Started a separate thread as the first one diverged from the initial question. I wanted to give an update where I am. This is a log of the first 4 instructions in the BIOS.
JMP 0xf000:0xe05b
MOV AX, 0x40
MOV DS, AX
MOV WORD [0x472], 0x0
it took me a while to get here because I am building a system that allows me to possibly expand it later to other CPUs. So I built a very simple stack based scripting language (very simple!) that controls the emulation of the 3 main units: EU, EA and BIU. To see how this works, lets look at a line from the log below
Cycle 12 T4 0xffff2 0xe0 >P [ 0xe0 xxxx xxxx xxxx ] waiting for data { imm execute delay }
This means we are in cycle 12 (type T4) and we are reading from bus at memory address 0xffff2 and we just read value 0xe0. We put that into the prefetch buffer (>P) which looks like this [ 0xe0 xxxx xxxx xxxx ] (xxxx means empty prefetch slot). The state of the EU is "waiting for data" and the stack based script I am executing for this instruction has the following steps: imm, execute and delay. It gets more interesting at cycle 52 where after EU executes the decoding of the rmmode it added few more steps in the script to be: { ea read imm execute delay } .
This system allows me to describe all instructions and properly execute them as the 8088 would do.
Sure there are some differences right now with the real 8088, such as the prefetch is locked halfway though the JMP not at the end and maybe the prefetch is read 1 cycle later after being filled in than what I do, but those are details that I can fix later as long as my system is sound and solid.
Oh and I do not think this is too slow, it sounds complicated but actually the code is quite simple.
<SYSTEM HARD RESET>Cycle 1 T1 [ xxxx xxxx xxxx xxxx ] { decode }Cycle 2 T2 [ xxxx xxxx xxxx xxxx ] { decode }Cycle 3 T3 [ xxxx xxxx xxxx xxxx ] { decode }Cycle 4 T4 0xffff0 0xea >P <P [ xxxx xxxx xxxx xxxx ] new opcode 0xea { imm execute delay }Cycle 5 T1 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 6 T2 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 7 T3 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 8 T4 0xffff1 0x5b >P [ 0x5b xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 9 T1 <P [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 10 T2 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 11 T3 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 12 T4 0xffff2 0xe0 >P [ 0xe0 xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 13 T1 <P [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 14 T2 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 15 T3 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 16 T4 0xffff3 0x 0 >P [ 0x00 xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 17 T1 <P [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 18 T2 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 19 T3 [ xxxx xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 20 T4 0xffff4 0xf0 >P [ 0xf0 xxxx xxxx xxxx ] waiting for data { imm execute delay }Cycle 21 T1 <P [ xxxx xxxx xxxx xxxx ] { execute delay }Cycle 22 T2 [ xxxx xxxx xxxx xxxx ] { delay }Cycle 23 T3 [ xxxx xxxx xxxx xxxx ] executing { delay }Cycle 24 T4 0xfe05b 0xb8 >P [ 0xb8 xxxx xxxx xxxx ] executing { delay }Cycle 25 T1 [ 0xb8 xxxx xxxx xxxx ] executing { delay }Cycle 26 T2 [ 0xb8 xxxx xxxx xxxx ] executing { delay }Cycle 27 T3 [ 0xb8 xxxx xxxx xxxx ] executing { delay }Cycle 28 T4 0xfe05c 0x40 >P [ 0xb8 0x40 xxxx xxxx ] executing { delay }Cycle 29 T1 [ 0xb8 0x40 xxxx xxxx ] executing { delay }Cycle 30 T2 [ 0xb8 0x40 xxxx xxxx ] executing { delay }Cycle 31 T3 [ 0xb8 0x40 xxxx xxxx ] executing { delay }Cycle 32 T4 0xfe05d 0x 0 >P [ 0xb8 0x40 0x00 xxxx ] executing { delay }Cycle 33 T1 [ 0xb8 0x40 0x00 xxxx ] executing { delay }Cycle 34 T2 [ 0xb8 0x40 0x00 xxxx ] executing { delay }Cycle 35 T3 [ 0xb8 0x40 0x00 xxxx ] executing { delay }Cycle 36 T4 0xfe05e 0x8e >P [ 0xb8 0x40 0x00 0x8e ] executing { delay }Cycle 37 T1 [ 0xb8 0x40 0x00 0x8e ] executing { delay }Cycle 38 T2 [ 0xb8 0x40 0x00 0x8e ] executing { decode }Cycle 39 T3 <P [ 0x40 0x00 0x8e xxxx ] new opcode 0xb8 { imm execute delay }Cycle 40 T4 0xfe05f 0xd8 <P >P [ 0x00 0x8e 0xd8 xxxx ] waiting for data { imm execute delay }Cycle 41 T1 <P [ 0x8e 0xd8 xxxx xxxx ] { execute delay }Cycle 42 T2 [ 0x8e 0xd8 xxxx xxxx ] { delay }Cycle 43 T3 [ 0x8e 0xd8 xxxx xxxx ] executing { delay }Cycle 44 T4 0xfe060 0xc7 >P [ 0x8e 0xd8 0xc7 xxxx ] executing { delay }Cycle 45 T1 [ 0x8e 0xd8 0xc7 xxxx ] executing { delay }Cycle 46 T2 [ 0x8e 0xd8 0xc7 xxxx ] executing { decode }Cycle 47 T3 <P [ 0xd8 0xc7 xxxx xxxx ] new opcode 0x8e { rmmode execute delay }Cycle 48 T4 0xfe061 0x 6 >P <P [ 0xc7 0x06 xxxx xxxx ] decode rmmode 0xd8 { execute delay }Cycle 49 T1 [ 0xc7 0x06 xxxx xxxx ] { delay }Cycle 50 T2 [ 0xc7 0x06 xxxx xxxx ] executing { delay }Cycle 51 T3 [ 0xc7 0x06 xxxx xxxx ] executing { decode }Cycle 52 T4 0xfe062 0x72 >P <P [ 0x06 0x72 xxxx xxxx ] new opcode 0xc7 { rmmode imm execute delay }Cycle 53 T1 <P [ 0x72 xxxx xxxx xxxx ] decode rmmode 0x6 { ea read imm execute delay }Cycle 54 T2 <P [ xxxx xxxx xxxx xxxx ] EA waiting for data EA calculation { ea read imm execute delay }Cycle 55 T3 [ xxxx xxxx xxxx xxxx ] EA waiting for data EA calculation { ea read imm execute delay }Cycle 56 T4 0xfe063 0x 0 >P [ 0x00 xxxx xxxx xxxx ] EA waiting for data EA calculation { ea read imm execute delay }Cycle 57 T1 <P [ xxxx xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 58 T2 [ xxxx xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 59 T3 [ xxxx xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }
Cycle 60 T4 0xfe064 0x 0 >P [ 0x00 xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 61 T1 [ 0x00 xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 62 T2 [ 0x00 xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 63 T3 [ 0x00 xxxx xxxx xxxx ] EA calculation { ea read imm execute delay }Cycle 64 T4 0xfe065 0x 0 >P [ 0x00 0x00 xxxx xxxx ] { read imm execute delay }Cycle 65 T1 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 66 T2 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 67 T3 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 68 T4 0x00472 0x 0 <M [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 69 T1 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 70 T2 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 71 T3 [ 0x00 0x00 xxxx xxxx ] waiting for data { read imm execute delay }Cycle 72 T4 0x00473 0x 0 <M [ 0x00 0x00 xxxx xxxx ] { imm execute delay }Cycle 73 T1 [ 0x00 0x00 xxxx xxxx ] { execute delay }Cycle 74 T2 [ 0x00 0x00 xxxx xxxx ] { delay }Cycle 75 T3 [ 0x00 0x00 xxxx xxxx ] executing { delay }Cycle 76 T4 0xfe066 0xfa >P [ 0x00 0x00 0xfa xxxx ] executing { decode }
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