topic Re: Assembly langauge code or C code in 8-bit Microcontrollers

Assembly langauge code or C code

venki — Wed, 04 Apr 2007 14:09:56 GMT

Hi,

I have source code read from MC08GP32. can we convert these codes in assembly Langauge or C Language.

Venki

S1I22515.s19

Message Edited by t.dowe on 2009-09-04 02:14 PM

Re: Assembly langauge code or C code

peg — Wed, 04 Apr 2007 15:48:51 GMT

Hi venki,

For this you need a dissassembler. There is one available in the free tools from www.pemicro.com or you can use the ICD from within the package for the GP32. You can also download Codewarrior from this site which will enable you to do this (and a lot more!).

I did this using decoder.exe from within Codewarrior which produced the included listing file.

Obviously you need to do a LOT more work than this to get a readable/understandable programme.

S1I22515.lst

Message Edited by t.dowe on 2009-09-04 02:16 PM

Re: Assembly langauge code or C code

Alban — Wed, 04 Apr 2007 18:55:42 GMT

lst files are now allowed.

Re: Assembly langauge code or C code

Curt — Wed, 04 Apr 2007 21:01:16 GMT

Hi venki.

If you follow Peg's advice and can download a free "special edition" of CodeWarrior from the Freescale web site, you will not only get an assembler manual and tools -- but also a simulator that will let you practice writing, assembling and executing programs in assembly language.

This is one of those "bargains" that will make you say -- "Wow!"

Regards,

Curt

Re: Assembly langauge code or C code

bigmac — Wed, 04 Apr 2007 21:29:56 GMT

Hello Venki,

The disassembled code from your original .S19 file (the code actually starts about half way through the created file) appears to be the result of compiled and linked C code. This is probably not a good place to start learning about the structure of an assembly program. I think you will need to start with the actual source code for much simpler assembly programs.

Regards,

Mac

Re: Assembly langauge code or C code

venki — Thu, 05 Apr 2007 14:19:25 GMT

Dear Mac,

Pls let me know the best way to get either c code or Assembly code from the file attached.

Regards

Venki

Re: Assembly langauge code or C code

peg — Thu, 05 Apr 2007 15:37:10 GMT

Hi venki,

I have already given you the assembly and told you how to do it yourself.

What Mac is saying (and I tend to agree it is possible) is that the code supplied looks as though it may have started out as C code.

It is very difficult to disassemble machine code to readable assembly, but it always possible due to the 1 to 1 relationship. It is virtually impossible to convert machine code to c code!

The problem that Mac is trying to point out is that if the code started from c code it makes the conversion of the machine code to assembly even more difficult than it already is.

If you really have to do this it is going to take many many hours of painstaking work. The difficulty level will depend on your knowledge of what it is actually supposed to do and the details of the hardware connected to the original MCU.

Re: Assembly langauge code or C code

venki — Thu, 05 Apr 2007 16:32:16 GMT

Dear Peg,

Our assembly code starts from $8000,which is starting address of Flash Memory then we should not have any confusion that assembly code what we achieved is what we required.I will take pain of undestanding as i know the function & hardware well.Let me know what the upper half portion of code resembles.Please confirm whether the assembly code what we achieved is what we needed.

Regards

Venki

Re: Assembly langauge code or C code

peg — Thu, 05 Apr 2007 18:24:50 GMT

Hi venki,

Yes the FLASH is programmed starting at $8000 which is the start address of the flash for this device.

However programme execution starts at $80E8 as defined by the double byte programmed at $FFFE which is the reset vector. This makes sense in that the byte above this is RTS.

I have taken the trouble to form a rough vector table for you. Going through this table you can see that although all vectors have handler routines a lot of them simply disable that particular interrupt.

From here you can make a start at breaking the code up into small manageable chunks.

Another technique is to look for RTS and RTI and seperate out these subroutines.

One of the first things is to replace all the absolute addresses in the register areas and replace them with there register names.

The code above approx. $CF00 looks like it is data rather than code and there seems to be a lot of it. Does this make sense to have this much hard coded data?

Anyway, good luck I do not envy your job.

Message Edited by peg on 2007-04-0509:25 PM

vecttabl.txt

Message Edited by t.dowe on 2009-09-04 02:17 PM

Re: Assembly langauge code or C code

venki — Thu, 05 Apr 2007 19:02:19 GMT

Dear Peg,

Thanks for your valueble effort in confirming aboat the code.You have not mentioned anything aboat Code above assembly code.

Regards

venki

Re: Assembly langauge code or C code

mke_et — Thu, 05 Apr 2007 19:39:27 GMT

I haven't tried the disassembler yet but I have a couple of questions.

Is it a labeling disassembler?

And does it allow multiple passes? That is, can you look at a 'first pass' and do things like define strings and change label names and such and then run another pass on it?

Mike

Re: Assembly langauge code or C code

bigmac — Thu, 05 Apr 2007 20:28:07 GMT

Hello Venki,

Within the listing file, the first half of the file contains a "memory dump" of each line of the .S19 file, one line at a time. It can be ignored, since your interest is with the disassembled code.

I am curious as to what you hope to achieve with the disassembly.

Once you have separated the code into the various sub-routines, identify those "low level" routines that do not call any other sub-routines. Then attempt to identify what each of these does. The routines that read or write peripheral registers may be easier to decode. I suggest you add copious comments as you work through the code.

I also don't envy your task of making sense of about 27K of code - I have previously reverse engineered projects with about 1K to 2K of code that was originally written in assembler (and not compiled from C), and this was tedious and time consuming enough.

Regards,

Mac

Re: Assembly langauge code or C code

Curt — Thu, 05 Apr 2007 21:44:29 GMT

One thing for sure though Venki: if you actually manage to dis-compile a 27K program you will be a bonafide expert in several areas (assembly language the least of them).

It will be a bit like trying to reconstruct your program from a listing that's been through the shredder twice -- or rewriting Kafka's _The Trial_ given a box of the letters contained in the original book

Re: Assembly langauge code or C code

peg — Fri, 06 Apr 2007 05:21:47 GMT

Hi Mike,

I don't think it is very clever at all, but I have never really tried to learn how to use it properly.

For the 08 I have only ever wanted to disassemble small sections of code and figured it was easier to work on the first pass by hand than learn how to automate it.

Obviously with a job the size of venki's I would be reading every word of help I could find.

I was actually hoping someone more knowledgeable was going to jump in here and suggest some more powerful software (or methods) to achieve this.

Re: Assembly langauge code or C code

venki — Sat, 07 Apr 2007 13:53:38 GMT

Dear Peg,

Rough Vector table which you have created correspond to opcode & operands of the instruction infront of it.I dont understand how vectors are handled

Regards

Venki

Re: Assembly langauge code or C code

peg — Mon, 09 Apr 2007 09:07:34 GMT

Hi venki,

The vector table at the very top of memory holds the interrupt vectors for the various interrupt sources within the device. You should read the chapter on interrupts in the text I referenced before for a full explanation. I will attempt to give rough explanation here that glosses over some of the specifics and just give you the stuff you need now.

The vector table I gave you has three columns the first is the address within the device and the second column is the contents of that address, and the next, in word format. The third is the description

The simplest one is the reset vector at $FFFE. On power up or reset the programme counter will be loaded with the address stored here and execution will begin from there.

Another one is the SCIRX vector.

Say the programme is running and the serial port recieves a character. This character will need to processed quite quickly in case there are others coming in right behind it. The best way to do this is use interrupts. When setup, and the character comes in, a SCIRX interrupt will be generated and registers and the current address of programme execution is stored away in a piece of RAM called the stack. Then the programme counter is loaded with $85CC (in this case). Execution will then jump to there and continue until an RTI is found. This then gets the info back of the stack and the programme continues as before.

The code at 85CC (I haven't looked in this case) possible just stores the incoming character into a buffer and checks what it was to see if it should do anything else (possible a CR would mean the end of a string etc)

So in the code you should find many "interrupt routines" that start at addresses in the second column and continue up to a RTI. You could start here, seperate all the routines out from each other and work out which ones do something useful and which ones are just there for safety (just in case the interrupt should trigger even though it is not intended to do so).

I hope I have made some sense here and helped you out, you have a long, long way to go...

Message Edited by peg on 2007-04-0912:11 PM

Re: Assembly langauge code or C code

venki — Mon, 09 Apr 2007 10:32:11 GMT

Dear Peg,

I apologise for not giving you correct information what i inteded to.What i mean to say is whatever address

(8564) is infront of Vector (FFDC) is opcode,operand of instuction(TPA) whose opcode is 85.

Refering to your vector table,

Instuction opcode operand

FFDC 8564 timebase    TPA                      85
FFDE 85D7 adc             LSR 133,X           64              85
FFE0 85D2 kbi                STA                     D7             85D2
FFE2 85CF sci tx            TPA                     85
FFE4 85CC sci rx           STX $85CC         CF            85CC
FFE6 85B9 sci err           TPA                     85
FFE8 85B4 spi tx             ADC $85             B9            85
FFEA 85AD spi rx            AND $85             B4            85
FFEC 8594 tim2 oflow     BSR *-121          AD            85
FFEE 858F t2ch1             TXS                     94
FFF0 858A t2ch0              TPA                     85
FFF2 8571 t1 oflow           WAIT                   8F
FFF4 856C t1ch1              TPA                     85
FFF6 8567 t1ch0               PULH                  8A
FFF8 855F pll                    TPA                    85
FFFA 855A irq                    DECX                5A
FFFC 80E8 swi                  EOR 128,X        E8           80
FFFE 80E8 reset               EOR 0,X            E8           00

I Feel you have formed a vector table (Address) with opcode & operand of instuction in front of it.

Regards

Venki

Re: Assembly langauge code or C code

peg — Mon, 09 Apr 2007 14:03:45 GMT

Hi venki,

No! What I have done is correct!

The disassembler does not know about the flash area reserved for the vector table so it has simply blindly attempted to convert the data here into code.

The note I made before about the code after a certain address being data is similar to this. The programmer was using an area of flash for data (not code) but the disassembler does not know about this either and just blindly attemps to convert it. You will see many illegal opcodes in this area. This is also a problem in that it takes some time for the disassemble to fall back into sync after these areas.

Re: Assembly langauge code or C code

venki — Mon, 09 Apr 2007 14:11:48 GMT

Dear Peg,

Thanks it is clear now.

Regards

Venki

Re: Assembly langauge code or C code

venki — Tue, 10 Apr 2007 09:51:34 GMT

Dear Peg,

As we noticed code above $CF00 Contains data.It is not fair enough to have so much hard coded data

in flash.1)What are the different options to keep these data?

2) Means of transfering this data

Regards

Venki