source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Device/IDE/IdeDmaBlock.asm@ 617

; Project name  :   XTIDE Universal BIOS
; Description   :   IDE Read/Write functions for transferring block using DMA.
;                   These functions should only be called from IdeTransfer.asm.

;
; XTIDE Universal BIOS and Associated Tools
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2013 by XTIDE Universal BIOS Team.
;
; 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 2 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.
; Visit http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; IdeDmaBlock_WriteToXTCF
;   Parameters:
;       CX:     Block size in 512 byte sectors
;       DX:     XTCF Base Port Address
;       ES:SI:  Physical address to buffer to receive data
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX, BX, CX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IdeDmaBlock_WriteToXTCF:
    xchg    si, di
    mov     bl, CHANNEL_3 | READ | AUTOINIT_DISABLE | ADDRESS_INCREMENT | DEMAND_MODE
    call    TransferBlockToOrFromXTCF
    xchg    di, si
    ret


;--------------------------------------------------------------------
; IdeDmaBlock_ReadFromXTCF
;   Parameters:
;       CX:     Block size in 512 byte sectors
;       DX:     XTCF Base Port Address
;       ES:DI:  Physical address to buffer to receive data
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX, BX, CX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
IdeDmaBlock_ReadFromXTCF:
    mov     bl, CHANNEL_3 | WRITE | AUTOINIT_DISABLE | ADDRESS_INCREMENT | DEMAND_MODE
    ; Fall to TransferBlockToOrFromXTCF


;--------------------------------------------------------------------
; TransferBlockToOrFromXTCF
;   Parameters:
;       BL:     Mode byte for DMA Mode Register
;       CX:     Block size in 512 byte sectors
;       DX:     XTCF Base Port Address
;       ES:DI:  Physical address to buffer to receive data
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX, BX, CX, DX
;--------------------------------------------------------------------
TransferBlockToOrFromXTCF:
    ; 8-bit DMA transfers must be done within 64k physical page.
    ; XT-CF support maximum of 64 sector (32768 bytes) blocks in DMA mode
    ; so we never need to separate transfer to more than 2 separate DMA operations.

    ; Load XT-CFv3 Control Register port to DX
    add     dl, XTCF_CONTROL_REGISTER

    ; convert sectors in CX to BYTES
%ifdef USE_186
    shl     cx, 9                                   ; CX = Block size in BYTEs
%else
    xchg    cl, ch
    shl     cx, 1
%endif

    ; Calculate bytes for first page
    mov     ax, di
    neg     ax          ; 2s complement

    ; If DI was zero carry flag will be cleared (and set otherwise)
    ; When DI is zero only one transfer is required since we've limited the
    ; XT-CFv3 block size to 32k
    jnc     SHORT StartDMAtransferForXTCFwithDmaModeInBL

    ; CF was set, so DI != 0 and we might need one or two transfers
    cmp     cx, ax                                          ; if we won't cross a physical page boundary...
    jbe     SHORT StartDMAtransferForXTCFwithDmaModeInBL    ; ...perform the transfer in one operation

    ; Calculate how much we can transfer on first and second rounds
    xchg    cx, ax      ; CX = BYTEs for first page
    sub     ax, cx      ; AX = BYTEs for second page
    push    ax          ; Save bytes for second transfer on stack

    ; Transfer first DMA page
    call    StartDMAtransferForXTCFwithDmaModeInBL
    pop     cx                                      ; Pop size for second DMA page
    ; Fall to StartDMAtransferForXTCFwithDmaModeInBL


;--------------------------------------------------------------------
; StartDMAtransferForXTCFwithDmaModeInBL
;   Parameters:
;       BL:     Byte for DMA Mode Register
;       CX:     Number of BYTEs to transfer (1...32768 since max block size is limited to 64)
;       DX:     XT-CFv3 Control Register
;       ES:     Bits 3..0 have physical address bits 19..16
;       DI:     Physical address bits 15..0
;   Returns:
;       ES:DI updated (CX is added)
;   Corrupts registers:
;       AX, CX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
StartDMAtransferForXTCFwithDmaModeInBL:
    ; Program 8-bit DMA Controller
    ; Disable Interrupts and DMA Channel 3 during DMA setup
    mov     al, SET_CH3_MASK_BIT
    cli                                 ; Disable interrupts - programming must be atomic
    out     MASK_REGISTER_DMA8_out, al  ; Disable DMA Channel 3

    ; Set DMA Mode (read or write using channel 3)
    mov     al, bl
    out     MODE_REGISTER_DMA8_out, al

    ; Send start address to DMA controller
    mov     ax, es
    out     PAGE_DMA8_CH_3, al
    mov     ax, di
    out     CLEAR_FLIPFLOP_DMA8_out, al                         ; Reset flip-flop to low byte
    out     BASE_AND_CURRENT_ADDRESS_REGISTER_DMA8_CH3_out, al  ; Low byte
    mov     al, ah
    out     BASE_AND_CURRENT_ADDRESS_REGISTER_DMA8_CH3_out, al  ; High byte

    ; Set number of bytes to transfer (DMA controller must be programmed number of bytes - 1)
    mov     ax, cx
    dec     ax                                                  ; DMA controller is programmed for one byte less
    out     BASE_AND_CURRENT_COUNT_REGISTER_DMA8_CH3_out, al    ; Low byte
    mov     al, ah
    out     BASE_AND_CURRENT_COUNT_REGISTER_DMA8_CH3_out, al    ; High byte

    ; Enable DMA Channel 3
    mov     al, CLEAR_CH3_MASK_BIT
    out     MASK_REGISTER_DMA8_out, al                          ; Enable DMA Channel 3
    sti                                                         ; Enable interrupts

    ; Update physical address in ES:DI - since IO might need several calls through this function either from here
    ; if crossing a physical page boundary, or from IdeTransfer.asm if requested sectors was > PIOVARS.wSectorsInBlock
    ; We update the pointer here (before the actual transfer) to avoid having to save the byte count on the stack
    mov     ax, es                      ; copy physical page address to ax
    add     di, cx                      ; add requested bytes to di
    adc     al, 0                       ; and increment physical page address, if required
    mov     es, ax                      ; and save it back in es

    ; XT-CF transfers 16 bytes at a time. We need to manually start transfer for every block by writing (anything)
    ; to the XT-CFv3 Control Register, which raises DRQ thereby passing system control to the 8237 DMA controller.
    ; The XT-CFv3 logic releases DRQ after 16 transfers, thereby handing control back to the CPU and allowing any other IRQs or
    ; DRQs to be serviced (which, on the PC and PC/XT will include DRAM refresh via DMA channel 0).  The 16-byte transfers can
    ; also be interrupted by the DMA controller raising TC (i.e. when done).  Each transfer cannot be otherwise interrupted
    ; and is therefore atomic (and hence fast).

%if 0   ; Slow DMA code - works by checking 8237 status register after each 16-byte transfer, until it reports TC has been raised.
ALIGN JUMP_ALIGN
.TransferNextBlock:
    cli                                 ; We want no ISR to read DMA Status Register before we do
    out     dx, al                      ; Transfer up to 16 bytes to/from XT-CF card
    in      al, STATUS_REGISTER_DMA8_in
    sti
    test    al, FLG_CH3_HAS_REACHED_TERMINAL_COUNT
    jz      SHORT .TransferNextBlock    ; All bytes transferred?
%else   ; Fast DMA code - perform computed number of transfers, then check DMA status register to be sure
    ; We'll divide transfers in 16-byte atomic transfers, so include any partial block, which will be terminated by the DMA controller raising T/C
    add     cx, BYTE 15

%ifdef USE_186
    shr     cx, 4
%else
    xchg    cx, ax
    mov     cl, 4
    shr     ax, cl
    xchg    cx, ax
%endif

ALIGN JUMP_ALIGN
.TransferNextDmaBlock:
    out     dx, al                      ; Transfer up to 16 bytes to/from XT-CF card
    loop    .TransferNextDmaBlock       ; dec CX and loop if CX > 0, also adds required wait-state
    inc     cx                          ; set up CX, in case we need to do an extra iteration
    in      al, STATUS_REGISTER_DMA8_in ; check 8237 DMA controller status flags...
    test    al, FLG_CH3_HAS_REACHED_TERMINAL_COUNT  ; ... for channel 3 terminal count
    jz      SHORT .TransferNextDmaBlock ; If not set, get more bytes
%endif

    ret