;
; JR-IDE Project
; - (c) 2020 Alan Hightower
;
; This program 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
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; 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 <http://www.gnu.org/licenses/>.
;

include "jride.inc"

DGROUP group _BIOSSEG,_TEXT,_CSUM

_BIOSSEG segment public use16 'CODE'

	; Few publics so symbols show up in map file
	public _bios_entry
	public _bios_start

	extrn  print_char : near
	extrn  print_string : near
	extrn  print_dec : near





	assume cs:_BIOSSEG, ds:nothing, es:nothing

	org    0

	; -------------------------------
	; ----- Start of Option ROM -----
	; -------------------------------

	; BIOS Pre-amble bytes

	db     0x55
	db     0xaa

	; Number of 512 blocks included in check-sum

	db     29 ; 14.5 KB

_bios_entry:

	jmp    _bios_start

	db     0x00

	; Signature Magic

	db     0x23, 0x83, 0xa8, 0x51

version:
	db     "2020-04-16", 0, 0


	org    020h

banner:
	db     LF, "PCjr jrIDE BIOS version ", 0

website:
	db     " (http://www.brutman.com/PCjr)", CR, LF, 0

CRLFMsg:
	db     CR, LF, 0


	; Option BIOS code start

_bios_start:

	push   es
	push   ds
	push   ax
	push   cx
	push   di

	mov    ax, cs
	mov    ds, ax
	mov    es, ax

	mov    ax, 3               ; 80x25 text mode
	int    10h                 ; set video mode

	mov    cx, JRIDE_SCRATCH_END
	mov    di, JRIDE_SCRATCH_RAM
	sub    cx, di
	xor    ax, ax              ; Clear drive parameter tables
	rep    stosb               ;   & transient variables

	mov    word ptr cs:[JRIDE_BOOT_MAGIC + 0], JRIDE_BOOT_MAGIC_LO
	mov    word ptr cs:[JRIDE_BOOT_MAGIC + 2], JRIDE_BOOT_MAGIC_HI


	; Announcement text

	mov    si, banner
	call   print_string

	mov    si, version
	call   print_string

	mov    si, website
	call   print_string


	; Choose a flash remap segment that isn't our CS

	mov    ax, cs
	cmp    ax, 0c000h
	je     alt_remap
	mov    word ptr cs:[JDA_REMAP_SEGMENT], 0c000h

alt_remap:
	mov    word ptr cs:[JDA_REMAP_SEGMENT], 0c400h

	call   displayMEM

	xor    ax, ax
	mov    ds, ax       ; ds -> vector table base (0x00000)

	cli











	sti

	; Clear virtual remap order and drive count.
	; This scheme should allow future support for multiple
	; hard drive BIOSs (SCSI) by adding an int 13h poll
	; check here first.

	mov    byte ptr cs:[JDA_DRIVE_COUNT],  0
	mov    byte ptr cs:[JDA_DRIVE0_INDEX], 0
	mov    byte ptr cs:[JDA_DRIVE1_INDEX], 0
	mov    byte ptr cs:[JDA_DRIVE2_INDEX], 0




















bios_done:

	pop    di
	pop    cx
	pop    ax
	pop    ds
	pop    es

	retf


memSizeMsg:
	db     "Base memory: ", 0

memSizeMsg2:
	db     "  Total memory: ", 0

displayMEM proc near public 

	push   ds
	mov    ax, 40h  ; BIOS Data Area (BDA)
	mov    ds, ax

	mov    si, memSizeMsg
	call   print_string

	mov    ax, ds:[BDA_MEMORY_SIZE]
	call   print_dec

	mov    si, memSizeMsg2
	call   print_string

	mov    ax, 736
	mov    ds:[BDA_ADAPTER_MEMORY], ax
	mov    ds:[BDA_MEMORY_SIZE], ax
	call   print_dec

	mov    si, CRLFMsg
	call   print_string

	pop    ds

	ret

displayMEM endp


driveMsg:
	db     CR, LF, "Drive ", 0

printDriveNum proc near public

	push   ax

	mov    di, driveMsg
	call   print_string

	mov    al, cs:[JDA_DRIVE_COUNT]
	add    al, '0'
	call   print_char

	mov    al, ':'
	call   print_char

	pop    ax

	ret

printDriveNum endp

_BIOSSEG ends

; Reserve the checksum byte at the end of the image
_CSUM segment public 'CSUM'
	db 0xff
_CSUM ends

	end