Author Topic: Review of task manager for scan and readfile on a simple protected state program  (Read 1013 times)

Offline Deskman243

  • Jr. Member
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  • Posts: 49
Good day everyone,

I'm happy to make a return of another contribtion to the community. Here I had a steady state protected mode program for simple scanning data functions. The goal was to make an auxiliary compiler for novice enthusiastic (like myself haha) for parsing things like data values and word processing.

This post is showing the design state where I'm trying to add a read file function right beside the scan functions. Curiously I couldn't get the buffer values to reserve when I run beside the scan code so I tried adding a standard task state to check in the larger state machine. Here the yield is getting me mixed results when tracking the values between states. I found that keeping track of values in the standard datapipes has te closest result so I left the value in cx to (mov) into the pre-protected mode state. Here however is where I get mixed results because when  I check the (cmp) gate to move to the new module it just falls through it without the logic!

I wanted to post a copy of this for review so I'm posting each part step by step and add the full reference for anyone else intrigued by this prospect.

First area is the stack functions for cmd_buffer given by cmd_prompt1 and the reference function given by cmd_prompt1.A
Code: [Select]

call Heap_Buffer
call Encoder

; call Paging

; call Filer

mov byte [Ref_CountA],0
call Parser.Blank

call Parser.Signature_Scan
call Parser.Assignment

call Decoder

call cmp_delta

;task segment prep code
;push cs
;push .A
push .B

pop word [Ref_Task_1]
;pop cx
;mov word [Ref_Task_1],cx

;call Domain.TaskA
jmp Domain.TaskA

jmp cmd_buffer

;native test code skip

;task prep code area

jmp poll_function

simple prep area gate for return tasking

Code: [Select]
; prep area
; prep area
Ref_Task1: dw 0



;preset code

;task segment preset

mov word [Ref_Task1],cx
;cmp word [Ref_Task1],0
cmp cx,0
jz short protectedGate1

jmp TaskA



mov si,String
call cmdprint


in al,0x92
or al,2
out 0x92,al


mov eax, cr0
or eax,1
mov cr0, eax

; mov [saved_segment],ds

jmp code32_post:__protected_mode_32

%include ''


cmp cx,0
jz protectedGate1

call Filer

jmp protectedGate1

.inc file for the read file test
Code: [Select]

;section .data
file db "text.txt",0

;section .bss

;test values
;referencer resb 4
;buffer  resb 1024

;referencer db 4
;buffer  db 1024
;buffer  db 100

;len     equ 1024
len     equ 100

;section .text

global Filer

    mov eax,5
    mov ebx,file
    mov ecx,0
    int 80h

    mov [referencer],eax
; read presets

    mov eax,3
    mov ebx,[referencer]   
    mov ecx,buffer   ;read to buffer
    mov edx,len      ;
    int 80h         ;read len db to buffer

    mov edx,eax       ;puts data counted

; write presets
    mov eax,4        ;write preset
    mov ebx,1        ;to primary stream
    mov ecx,buffer   ;from primary buffer
    int 80h         ;reserve all read scanned data from buffer

    mov eax,6        ;close file preset
    mov ebx,[referencer]       ;
    int 80h         ;

    mov eax,1
    mov ebx,0
    int 80h         


Pseudocode proof-of-concept on scan

Code: [Select]
int data1 = 12 _ int data2 = 23 _

check the page.Main values for yield

Currently I'm trying to debug this as native code. While I have experience with debuggers like gdb I sometimes run into unknowns such as when data segments jump outside of expected values in this case . If anyone else would like an explanation of my debug settings please let me know so I can clarify further testing.

Notice 1-
I got the machine steady but still not stable. the new file instructions stall when I (cmp) pass by exact value instead of reference. What's more curious is according to my gdb now the jump @ cmp goes into the 512 boot segment.

Code: [Select]
;    ReTimerOS
;    Copyright (C) 2022,2023  Christopher Hoy
; This file is part of ReTimerOS
;    ReTimerOS is free software: you can redistribute it and/or modify
;    it under the terms of the GNU General Public License as published by
;    the Free Software Foundation, either version 3 of the License, or
;    (at your option) any later version.
;    This program is distributed in the hope that it will be useful,
;    but WITHOUT ANY WARRANTY; without even the implied warranty of
;    GNU General Public License for more details.
;    You should have received a copy of the GNU General Public License
;    along with this program.  If not, see <>.

;%define REBASE_ADDRESS(A)  (0x7E00 + ((A) - protectedGate1))

%define BUILD_GDT_DESC(bounds,base,access,flags) \
((( base & 0x00FFFFFF) << 16) | \
(( base & 0xFF000000) << 32) | \
( bounds & 0x0000FFFF) | \
(( bounds & 0x000F0000) << 32) | \
(( access & 0xFF) << 40) | \
(( flags & 0x0F) << 52))

;[ORG 0x7E00]

[BITS 16]

;section .text

; prep area
Ref_Task1: dw 0



;preset code

;task segment preset

mov word [Ref_Task1],cx
;cmp word [Ref_Task1],0

;cmp cx,0
;jz short protectedGate1
cmp cx,0x8b76
jz TaskA

;jmp TaskA



mov si,String
call cmdprint


in al,0x92
or al,2
out 0x92,al


mov eax, cr0
or eax,1
mov cr0, eax

; mov [saved_segment],ds

jmp code32_post:__protected_mode_32

%include ''


cmp cx,0
jz protectedGate1

call Filer

jmp protectedGate1

mov ah,0x0E

int 0x10
cmp al,0
jnz cmdstring

;section .text

[bits 32]
; 32 bit protected mode
;    mov ax, 0x10
mov ax,data32_post
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
;    mov ss, ax
    ; restate cr3
    mov cr3, ebx
    ; restate esp
    mov esp, edx

mov cx,[gate_voucher]
cmp word [gate_voucher],0
jnz loopcheck
mov word [gate_voucher],1


jmp loopcheck

; jmp 0x8000


;    pusha
    ; save current esp to edx
    mov edx, esp
    ; jumping to 16 bit protected mode
    ; disable interrupts
    ; clear cr3 by saving cr3 data in ebx register
    xor ecx, ecx
    mov ebx, cr3
    mov cr3, ecx

jmp code16_post:__protected_mode_16

[bits 16]
; 16 bit protected mode
    ; jumping to 16 bit real mode

xor eax,eax
xor ecx,ecx

;   mov ax, 0x38
mov cx,data16_post

; mov ax,0

    mov ds, cx
    mov es, cx
    mov fs, cx
    mov gs, cx
    mov ss, cx
    ; turn off protected mode
    ; set bit 0 to 0

;tss prep
mov bp,word [Ref_Task1]

    mov eax, cr0
    and al,  ~0x01
    mov cr0, eax

; jmp 0x0:REBASE_ADDRESS(__real_mode_16)
; jmp 0x0:REBASE_ADDRESS(0x0000_9000)

jmp 0x8000
; jmp 0x9C00

; jmp 0x9e00

; jmp 0xa000

; jmp 0xc000

; jmp 0xee00

; jmp 0xf400

; jmp 0xf000

;section .data

String: db 'platform 2',10,13,0
checkString: db 'check',10,13,0

dq BUILD_GDT_DESC(0,0,0,0)
dq BUILD_GDT_DESC(0x0000ffff,0,10011010b,1100b)
dq BUILD_GDT_DESC(0x0000ffff,0,10010010b,1100b)
dq BUILD_GDT_DESC(0x0000ffff,0,10011010b,1000b)
dq BUILD_GDT_DESC(0x0000ffff,0,10010010b,1000b)


code32_post: equ gdt32code -gdt32
data32_post: equ gdt32data -gdt32
code16_post: equ gdt16code -gdt32
data16_post: equ gdt16data -gdt32

; tss32_post: equ gdt32tss -gdt32

gdt32Len: equ $-gdt32
gdt32Ptr: dw gdt32Len-1
dd gdt32

save_cr0 dd 0
save_cr3 dd 0
saved_segment resd 0
gate_voucher dw 0
saved_stack resw 0

dw 0x03ff
dd 0

referencer: times 4 db 4
buffer: times 100 db 1

times 512-($-$$) db 0

;%include ''

Notice 2
I managed to get to the right task area when I push and pop the value but now I'm getting stuck on the call inside the task

Code: [Select]
push cx
pop bx

cmp cx,bx
jz TaskA

Notice 3
Had to fix the bound values to fit the file segments (1024->100) and currently testing the instruction segment sequences.
« Last Edit: January 12, 2024, 01:02:57 AM by Deskman243 »