page 60,132
title start1 - simple start-up code
;**************************************************************;
; ;
; start1.asm ;
; ;
; start-up for stand-alone C code - Turbo C/C++ version ;
; ;
; created: November 17, 1990 ;
; ;
; Copyright (c) 1990 ;
; Pasquale J. Villani ;
; All Rights Reserved ;
; ;
;**************************************************************;
_TEXT segment byte public 'CODE'
assume cs:_TEXT ; small model
_TEXT ends
_DATA segment word public 'DATA'
DGROUP group _DATA,_BSS,_BSSEND ; small model
assume ds:DGROUP,ss:DGROUP
_DATA ends
_BSS segment word public 'BSS'
_BSS ends
_BSSEND segment byte public 'STACK'
_BSSEND ends
_TEXT segment byte public 'CODE'
extrn _main:near ; C entry point
extrn _hdw_init:near ; Hardware init (asm or C)
;
; entry:
; Our ROM madule's entry point. This should be used as the
; 'jmp far ptr entry' at the top of ROM.
;
entry proc far
public entry;
;
; First order of business is the initialization of the
; machine itself. This is basically the initialization
; of any segment registers that the processor needs for
; proper operation. On an 80X86 class processor, this is
; usually initializing the segmentation registers, going
; to the proper mode (i. e. protected, etc.) for
; 80[234]86 processors, etc. This file is for an 8086 or
; 8088 machine (or any other in real mode). Segment
; registers are the only processor initialization.
;
; NOTE: the cs register is not initialized because the
; processor itself initializes the first cs, followed
; by the far jump changing it to point to segment entry.
;
cli ; prevent interrupts while starting
mov ax,DGROUP ; initialize the segment registers
mov ds,ax
mov ss,ax
mov es,ax
;
; Once the processor is initialized, it usually requires
; the proper setting of the stack pointer(s). For the
; 8086 case, all we need is to initialize the sp and bp
; registers.
;
mov sp,offset DGROUP:tos
mov bp,sp
;
; We are now ready to make any special hardware
; initialization. This includes initializing the interrupt
; vector table, moving the data segment to RAM and
; initializing the BSS to zero to match C programming
; conventions. This should end with a call to __hdw_init
; to initialize I/O, etc.
call near ptr __hdw_init; initialize the system without ints
sti ;now enable them
;
; After the hardware is initialized, we wish to enter
; main(). This is accomplished by building the stack for
; envp, argv and argc. This is a convienent mechanism
; for passing system configuration, dip switch settings,
; etc. to our C code.
;
mov ax,offset env ; envp for this example
push ax
mov ax,offset args ; argv for this example
push ax
mov ax,2 ; argc = 2
push ax
call near ptr _main ; finally enter C code
add sp,6 ; clean stack
;
; If main should return, we need a mechanism to catch this
; condition. Depending on the system design, we should
; alarm, restart, etc., therefore, the following code
; is very implementation dependant. In our case, all we
; want to do is call exit with a special -1 exit code.
;
mov ax,-1
push ax
call near ptr _exit
jmp $ ; belt and suspenders
entry endp
;
; exit:
; Where to go for error conditions (typically) or shutdown
; conditions. This code is very implementaion sensitive, since
; we may want to light LEDs and sound alarms. In this case, we'll
; only silently stop. In certain cases, we may want to only
; display a message and restart. This should be decided upon
; during system design.
;
_exit proc near
public _exit
cli
hlt
jmp _exit
_exit endp
T_EXT ends
_DATA segment word public 'DATA'
env0 label byte
db 'ENV=ROM',0
arg0 label byte
db 'ex0s', 0
arg1 label byte
db 'rom', 0
env label word
dw DGROUP:env0
dw 0
args label word
dw DGROUP:arg0
dw DGROUP:arg1
dw 0
_DATA ends
;
; The stack segment. This size should be adjusted to fit
; any particular system requirements.
;
_STACK SEGMENT
dw 512 dup (?)
tos label byte
dd (?) ; safety area
last label word ; must always be end of stack area
_STACK ENDS
_BSS segment word public 'BSS'
_errno label word ; c lib errno
public _errno
dw (?)
_BSS ends
_BSSEND segment byte public 'STACK'
_BSSEND ends
end