#(C) TechnicallyObsolete 2024
# GPL v3 License
#Based on 8088 BIOS  Copyright (C) 2010 - 2023 Sergey Kiselev.
;=========================================================================
; int_13 - BIOS floppy disk services
; Input:
;	AH = function
;		00h - Reset disk system
;		01h - Get status of last operation
;		02h - Read disk sectors
;		03h - Write disk sectors
;		04h - Verify disk sectors
;		05h - Format track
;		08h - Get drive parameters
;		15h - Get disk type
;		16h - Detect disk change
;		17h - Set disk type for format
;		18h - Set media type for format
;
; Note, all of these functions are handled by the STM32.
; Output:
;	- depends on function
;	- for most functions:
;		CF clear if successful
;			AH = 00h - successful completion
;		CF set on error
;			AH = error code
;-------------------------------------------------------------------------
	setloc	0EC59h			; INT 13 (Floppy) Entry Point

FPGA_REG_AL   equ 50h
FPGA_REG_AH   equ 51h
FPGA_REG_BL   equ 52h
FPGA_REG_BH   equ 53h
FPGA_REG_CL   equ 54h
FPGA_REG_CH   equ 55h
FPGA_REG_DL   equ 56h
FPGA_REG_DH   equ 57h
FPGA_REG_ES_L equ 58h
FPGA_REG_ES_H equ 59h
FPGA_REG_DI_L equ 5Ah
FPGA_REG_DI_H equ 5Bh
FPGA_REG_COPY equ 5Ch ;Used to specify which bytes to copy back
FPGA_REG_REQ  equ 5Dh
FPGA_REG_KBD  equ 5Eh
FPGA_REG_STS  equ 5Fh


int_13:
 ;Copy function params
  out FPGA_REG_AL, al
  mov al, ah
  out FPGA_REG_AH, al
  mov al, bl
  out FPGA_REG_BL, al
  mov al, bh
  out FPGA_REG_BH, al
  mov al, cl
  out FPGA_REG_CL, al
  mov al, ch
  out FPGA_REG_CH, al
  mov al, dl
  out FPGA_REG_DL, al
  mov al, dh
  out FPGA_REG_DH, al

  mov ax, es
  out FPGA_REG_ES_L, al

  mov al, ah
  out FPGA_REG_ES_H, al

  ;Now generate a request
  mov al, 13h
  out FPGA_REG_REQ, al

  ;Clock will now be stopped
  ;Once it resumes, register 5 will have a status code in it
  ;
  ;Update the carry flag accordingly
  clc
  in al, FPGA_REG_REQ
  cmp al, 00h
  jz copy_regs

  ;Didn't jump directly to COPY_REGS, so FPGA_REG_REQ != 0
  ;Set Carry flag to indicate something went wrong
  stc

copy_regs:

  ;Which registers should be copied back?
  ;REG_COPY = 0 -> AH, AL only
  ;         = 1 -> AH, AL, BL, CH, CL, DH, DL, ES:DI
  in al, FPGA_REG_COPY
  cmp al, 01h
  jz copy_large

copy_ah_al:
  in al, FPGA_REG_AH
  mov ah, al
  in al, FPGA_REG_AL
  jmp end

copy_large:

  ;BX
  in al, FPGA_REG_BL
  mov bl, al
  in al, FPGA_REG_BH
  mov bh, al

  ;CX
  in al, FPGA_REG_CL
  mov cl, al
  in al, FPGA_REG_CH
  mov ch, al

  ;DX
  in al, FPGA_REG_DL
  mov dl, al
  in al, FPGA_REG_DH
  mov dh, al

  ;ES
  in al, FPGA_REG_ES_H
  mov ah, al

  in al, FPGA_REG_ES_L
  ;AX now contains the new ES value
  mov es, ax

  ;DI
  in al, FPGA_REG_DI_H
  mov ah, al
  in al, FPGA_REG_DI_L
  ;AX now contains the new DI value
  mov di, ax

  ;Finally, restore the AL, AH values
  in al, FPGA_REG_AH
  mov ah, al
  in al, FPGA_REG_AL

end:
  iret