Question

Prelims in Assembly programming?

Asked by: Johncy

This is the starting of my assembly Program

      .486P

      INCLUDE MACROS.INC
      INCLUDE TIME.INC
      INCLUDE PORT80.inc

_VECTOR SEGMENT PUBLIC use16 'CODE'

      ASSUME CS:SEGGROUP

      EXTERN      startTest:NEAR


      org 0005bh            ;jump to post  entry point

      PORT80      POST_INTR_SEG_JUMP      ;post_f0h
      db      0eah
      public      resetVectorOffset
resetVectorOffset::
      dw      OFFSET startTest
      dw      0F000h


;
; Jump to F000:0000 and begin executing code there.  This address is where
; all of the normal test code for this xpress.rom is located.
;
      org      01FF0h
      db      0eah
      dw      0E05bh
      dw      0F000h                  ; Jump to F000:E05b

;
; Nothing below this point ever executes
;

      DB      BUILDDATE            ; Date of build
      DB      000h                  ; Unused byte
      DB      0FCh                  ; Mark AT Computer ID
      DB      000h                  ; Unused byte

_VECTOR ENDS

END

My CS is f000h.
Please tell me if my assumptions are right?
org command says that the program will start at f000:005b. - ?
PORT80      POST_INTR_SEG_JUMP - PORT80 is a macro.
After this is db 0eah. What does it represent?

resetVectorOffset::
      dw      OFFSET startTest
      dw      0F000h
What does it say?

;
; Jump to F000:0000 and begin executing code there.  This address is where
; all of the normal test code for this xpress.rom is located.
;
      org      01FF0h
      db      0eah
      dw      0E05bh
      dw      0F000h            ; Jump to F000:E05b

Here what does
org      01FF0h
db      0eah
say? No jump statement is present. How would it jump?


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Asked On
2003-12-17 at 02:29:46ID20828038
Tags

assembly

,

jump

Topic

Assembly Programming Language

Participating Experts
2
Points
100
Comments
10

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Answers

 

by: mtmikePosted on 2003-12-18 at 12:08:20ID: 9966908

0xEA is the opcode of a far jump. So,

  db 0eah
resetVectorOffset:
  dw OFFSET startTest
  dw 0F000h

jumps to startTest. The resetVectorOffset label is placed in the middle of the jmp instruction, most likely to save space in some other part of the code.

 

by: dimitryPosted on 2003-12-21 at 16:25:05ID: 9982669

Your code should be loaded to F000:E000 or FE00:0000.

    org     01FF0h          ; should present address FE00:1FF0 or F000:FFF0 or FFFF:0000
    db     0eah               ; <- Reset entry of x86
    dw     0E05bh
    dw     0F000h          ; Jump to F000:E05b
                                             |
                                             V
    org 0005bh             ; jump to post  entry point (if code is loaded to F000:E000)

    PORT80     POST_INTR_SEG_JUMP     ;post_f0h
    db     0eah              ; jumps to startTest (as mtmike has already mentioned)
    public     resetVectorOffset
resetVectorOffset:
    dw     OFFSET startTest
    dw     0F000h        

 

by: JohncyPosted on 2003-12-21 at 18:02:55ID: 9982897

My Bios code is 256 KB. My Flash memory is 32 Mbits. If my Flash is mapped to the lower address, at which location in Flash should I load this BIOS program? Should it be from 0xFFFFF-0xC0000 or some other?

 

by: dimitryPosted on 2003-12-22 at 05:26:17ID: 9984606

I have already written you that the point is that you can boot (I mean BIOS) only from one
physical media (or NOR flash, or DiskOnChip). Your x86 reset vector has ONLY one physical location: 0xFFFFFFF0. Let's take one step back.
There is no real DS or CS register in x86. It was in 8086, but now it doesn't exist.
x86 has 10 bytes hidden segment selector for each "segment" register.
4 bytes for base, 4 bytes for limit and 2 other have control information.
When x86 wakes up in real mode, "CS" segment selector will have next value:
   0xFFFF0000 for base and EIP = 0x0000FFF0
Therefore CPU fetchs first command from 0xFFFFFFF0. BUT first command that loads CS
(far jump for example) will change the "CS" segment selector from 0xFFFF0000 to the value
that has upper 12 bit zeroed. Therefore if you have far jump to 0xF000:0xE05B then
"CS" segment selector will have base value = 0x000F0000 that corresponds to your 8086
"understanding" of segment register.
  And now there is a big question: what is mapped to 0xFFFFFFF0 and what is mapped to 0x000F0000 ?
  But this is your H/W configuration...

 

by: JohncyPosted on 2003-12-22 at 18:08:48ID: 9988962

I have my Flash mapped to the lower address 0x00000000 - 0x003FFFFF.

 

by: dimitryPosted on 2003-12-22 at 23:04:01ID: 9989816

And how NS Readme suggests to map it ?

 

by: JohncyPosted on 2004-01-15 at 00:42:59ID: 10118570

As per the dorado schematic the flash is mapped to the lower address.

 

by: dimitryPosted on 2004-01-15 at 07:38:58ID: 10120889

Do you know web link to this schematics ?

 

by: JohncyPosted on 2004-01-15 at 22:51:41ID: 10127569

                     http://wwwd.national.com/National/developer.nsf/files/sc1200/$File/sc1200_ebga_tft_on_parallel.pdf

I have not used it as exactly. Flash rom is supported via the ISA interface and ethernet and video decoder via the PCI interface.
 

 

by: dimitryPosted on 2004-01-18 at 09:24:00ID: 10140945

You have two boot options (Jumper J3):
1) PLCC EEprom
2) DiskOnChip

However you can also "map" DiskOnChip to "low" memory region: 0xC8000-0xDFFFF by "mapping" GPIO20_DOC to
some address in this range. This range belongs to ISA bridge and your Flash is apped there too.

20120131-EE-VQP-002

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