DOS_Video/vgaCommon.c

// vgaCommon.c -- Shared VGA register programming
//
// Implements read/write access to the five standard VGA register
// groups. These are used by all chip-specific drivers for basic
// mode setup before enabling acceleration.
//
// Important timing note: on real hardware, some registers require
// specific sequencing (e.g. attribute controller must be reset via
// a read of Input Status 1 before writing the index). These
// functions handle the sequencing internally.

#include "vgaCommon.h"
#include "pci.h"

#include <dpmi.h>
#include <go32.h>
#include <pc.h>
#include <stdio.h>
#include <string.h>
#include <sys/farptr.h>
#include <sys/nearptr.h>

// VESA mode scoring weights (same as DVX)
#define MODE_SCORE_16BPP       100
#define MODE_SCORE_15BPP       90
#define MODE_SCORE_32BPP       85
#define MODE_SCORE_8BPP        70
#define MODE_SCORE_PREF_BPP    20
#define MODE_SCORE_EXACT_RES   10

// ============================================================
// Prototypes
// ============================================================

bool     dpmiMapFramebuffer(uint32_t physAddr, uint32_t size, DpmiMappingT *mapping);
void     dpmiUnmapFramebuffer(DpmiMappingT *mapping);
uint32_t pciSizeBar(uint8_t bus, uint8_t dev, uint8_t func, uint8_t barReg);
uint8_t  vgaAttrRead(uint8_t index);
void     vgaAttrReset(void);
void     vgaAttrWrite(uint8_t index, uint8_t val);
void     vgaBlankScreen(bool blank);
uint8_t  vgaCrtcRead(uint8_t index);
void     vgaCrtcLock(void);
void     vgaCrtcUnlock(void);
void     vgaCrtcWrite(uint8_t index, uint8_t val);
void     vgaDacReadColor(uint8_t index, uint8_t *r, uint8_t *g, uint8_t *b);
void     vgaDacWriteColor(uint8_t index, uint8_t r, uint8_t g, uint8_t b);
uint8_t  vgaGfxRead(uint8_t index);
void     vgaGfxWrite(uint8_t index, uint8_t val);
uint8_t  vgaMiscRead(void);
void     vgaMiscWrite(uint8_t val);
void     vgaRestoreTextMode(void);
uint8_t  vgaSeqRead(uint8_t index);
void     vgaSeqWrite(uint8_t index, uint8_t val);
bool     vesaFindAndSetMode(int32_t reqW, int32_t reqH, int32_t reqBpp, VesaModeResultT *result);
void     vgaWaitVRetrace(void);

// ============================================================
// dpmiMapFramebuffer
// ============================================================
//
// Maps a physical address region into the DJGPP near pointer
// address space via DPMI. This is the three-step process that
// every driver needs:
//   1. Map physical address to linear address
//   2. Lock the pages to prevent swapping
//   3. Enable near pointers for direct C pointer access
//
// Returns true on success. On failure, mapping->ptr is NULL.

bool dpmiMapFramebuffer(uint32_t physAddr, uint32_t size, DpmiMappingT *mapping) {
    __dpmi_meminfo info;

    memset(mapping, 0, sizeof(*mapping));

    info.address = physAddr;
    info.size    = size;

    if (__dpmi_physical_address_mapping(&info) != 0) {
        fprintf(stderr, "dpmiMap: Failed to map 0x%08lX (%lu bytes)\n",
                (unsigned long)physAddr, (unsigned long)size);
        return false;
    }

    __dpmi_meminfo lockInfo;
    lockInfo.address = info.address;
    lockInfo.size    = size;
    __dpmi_lock_linear_region(&lockInfo);

    if (__djgpp_nearptr_enable() == 0) {
        fprintf(stderr, "dpmiMap: Failed to enable near pointers\n");
        return false;
    }

    mapping->ptr        = (uint8_t *)(info.address + __djgpp_conventional_base);
    mapping->linearAddr = info.address;
    mapping->size       = size;

    return true;
}


// ============================================================
// dpmiUnmapFramebuffer
// ============================================================

void dpmiUnmapFramebuffer(DpmiMappingT *mapping) {
    if (mapping->ptr) {
        __djgpp_nearptr_disable();
        mapping->ptr = NULL;
    }
}


// ============================================================
// pciSizeBar
// ============================================================
//
// Determines the size of a PCI BAR by writing all 1s and reading
// back the mask. Saves and restores the original BAR value.

uint32_t pciSizeBar(uint8_t bus, uint8_t dev, uint8_t func, uint8_t barReg) {
    uint32_t saved = pciRead32(bus, dev, func, barReg);

    pciWrite32(bus, dev, func, barReg, 0xFFFFFFFF);
    uint32_t mask = pciRead32(bus, dev, func, barReg);
    pciWrite32(bus, dev, func, barReg, saved);

    // Decode: invert the writable bits, add 1
    mask &= 0xFFFFFFF0;  // mask off type bits

    if (mask == 0) {
        return 0;
    }

    return (~mask) + 1;
}


// ============================================================
// vesaFindAndSetMode
// ============================================================
//
// Enumerates VESA VBE modes, scores them against the requested
// resolution and bpp, sets the best match with LFB enabled, and
// returns the mode details. This replaces ~150 lines of identical
// code in every driver.

bool vesaFindAndSetMode(int32_t reqW, int32_t reqH, int32_t reqBpp, VesaModeResultT *result) {
    __dpmi_regs r;

    memset(result, 0, sizeof(*result));

    // Get VBE controller info
    _farpokeb(_dos_ds, __tb + 0, 'V');
    _farpokeb(_dos_ds, __tb + 1, 'B');
    _farpokeb(_dos_ds, __tb + 2, 'E');
    _farpokeb(_dos_ds, __tb + 3, '2');

    memset(&r, 0, sizeof(r));
    r.x.ax = 0x4F00;
    r.x.es = __tb >> 4;
    r.x.di = __tb & 0x0F;
    __dpmi_int(0x10, &r);

    if (r.x.ax != 0x004F) {
        fprintf(stderr, "vesaFindAndSetMode: VBE not available\n");
        return false;
    }

    // Copy mode list before 4F01h overwrites __tb
    uint16_t modeListOff = _farpeekw(_dos_ds, __tb + 14);
    uint16_t modeListSeg = _farpeekw(_dos_ds, __tb + 16);
    uint32_t modeListAddr = ((uint32_t)modeListSeg << 4) + modeListOff;

    uint16_t modes[256];
    int32_t  modeCount = 0;

    for (int32_t i = 0; i < 256; i++) {
        uint16_t mode = _farpeekw(_dos_ds, modeListAddr + i * 2);
        if (mode == 0xFFFF) {
            break;
        }
        modes[modeCount++] = mode;
    }

    // Score each mode and find the best
    uint16_t bestMode  = 0;
    int32_t  bestScore = -1;

    for (int32_t i = 0; i < modeCount; i++) {
        memset(&r, 0, sizeof(r));
        r.x.ax = 0x4F01;
        r.x.cx = modes[i];
        r.x.es = __tb >> 4;
        r.x.di = __tb & 0x0F;
        __dpmi_int(0x10, &r);

        if (r.x.ax != 0x004F) {
            continue;
        }

        uint16_t attr  = _farpeekw(_dos_ds, __tb + 0);
        int32_t  w     = _farpeekw(_dos_ds, __tb + 18);
        int32_t  h     = _farpeekw(_dos_ds, __tb + 20);
        int32_t  bpp   = _farpeekb(_dos_ds, __tb + 25);
        int32_t  pitch = _farpeekw(_dos_ds, __tb + 16);
        uint32_t phys  = _farpeekl(_dos_ds, __tb + 40);

        // Must have LFB and be a graphics mode
        if (!(attr & 0x0080) || !(attr & 0x0010)) {
            continue;
        }

        // Must meet requested resolution
        if (w < reqW || h < reqH) {
            continue;
        }

        // Only 8/15/16/32 bpp
        if (bpp != 8 && bpp != 15 && bpp != 16 && bpp != 32) {
            continue;
        }

        int32_t score = 0;

        if (bpp == 16)      { score = MODE_SCORE_16BPP; }
        else if (bpp == 15) { score = MODE_SCORE_15BPP; }
        else if (bpp == 32) { score = MODE_SCORE_32BPP; }
        else                { score = MODE_SCORE_8BPP; }

        if (bpp == reqBpp)               { score += MODE_SCORE_PREF_BPP; }
        if (w == reqW && h == reqH)      { score += MODE_SCORE_EXACT_RES; }

        if (score > bestScore) {
            bestScore          = score;
            bestMode           = modes[i];
            result->width      = w;
            result->height     = h;
            result->bpp        = bpp;
            result->pitch      = pitch;
            result->lfbPhysAddr = phys;
        }
    }

    if (bestScore < 0) {
        fprintf(stderr, "vesaFindAndSetMode: No suitable mode for %ldx%ldx%ld\n",
                (long)reqW, (long)reqH, (long)reqBpp);
        return false;
    }

    // Set the mode with LFB enabled (bit 14)
    memset(&r, 0, sizeof(r));
    r.x.ax = 0x4F02;
    r.x.bx = bestMode | 0x4000;  // bit 14 = enable LFB
    __dpmi_int(0x10, &r);

    if (r.x.ax != 0x004F) {
        fprintf(stderr, "vesaFindAndSetMode: Failed to set mode 0x%04X\n", bestMode);
        return false;
    }

    return true;
}


// ============================================================
// vgaAttrRead
// ============================================================
//
// The attribute controller is unusual: reading Input Status 1
// resets its flip-flop so the next write to 0x3C0 is treated as
// an index (not data). We must reset before every access.

uint8_t vgaAttrRead(uint8_t index) {
    inportb(VGA_INPUT_STATUS_1);
    outportb(VGA_ATTR_INDEX, index);
    return inportb(VGA_ATTR_DATA_R);
}


// ============================================================
// vgaAttrReset
// ============================================================
//
// Resets the attribute controller flip-flop by reading Input
// Status 1. After this, the next write to 0x3C0 is an index write.

void vgaAttrReset(void) {
    inportb(VGA_INPUT_STATUS_1);
}


// ============================================================
// vgaAttrWrite
// ============================================================
//
// Writes to the attribute controller. The flip-flop mechanism
// means we must: (1) read Input Status 1 to reset, (2) write
// the index to 0x3C0, (3) write the data to 0x3C0.
// Bit 5 of the index byte must be set to keep the palette
// address source enabled (otherwise the screen goes black).

void vgaAttrWrite(uint8_t index, uint8_t val) {
    inportb(VGA_INPUT_STATUS_1);
    outportb(VGA_ATTR_INDEX, index);
    outportb(VGA_ATTR_DATA_W, val);
}


// ============================================================
// vgaBlankScreen
// ============================================================
//
// Toggles the screen on/off by setting bit 5 of the sequencer
// clocking mode register. Blanking prevents visible garbage
// during mode transitions.

void vgaBlankScreen(bool blank) {
    uint8_t val = vgaSeqRead(VGA_SEQ_CLOCK_MODE);

    if (blank) {
        val |= VGA_SEQ_SCREEN_OFF;
    } else {
        val &= ~VGA_SEQ_SCREEN_OFF;
    }

    vgaSeqWrite(VGA_SEQ_CLOCK_MODE, val);
}


// ============================================================
// vgaCrtcLock
// ============================================================
//
// Re-enables CRTC write protection by setting bit 7 of the
// vertical sync end register.

void vgaCrtcLock(void) {
    uint8_t val = vgaCrtcRead(VGA_CRTC_V_SYNC_END);
    vgaCrtcWrite(VGA_CRTC_V_SYNC_END, val | 0x80);
}


// ============================================================
// vgaCrtcRead
// ============================================================

uint8_t vgaCrtcRead(uint8_t index) {
    outportb(VGA_CRTC_INDEX, index);
    return inportb(VGA_CRTC_DATA);
}


// ============================================================
// vgaCrtcUnlock
// ============================================================
//
// Disables CRTC write protection. Registers 0x00-0x07 of the
// CRTC are protected by bit 7 of the vertical sync end register
// (0x11). Clearing this bit allows writing to those registers.

void vgaCrtcUnlock(void) {
    uint8_t val = vgaCrtcRead(VGA_CRTC_V_SYNC_END);
    vgaCrtcWrite(VGA_CRTC_V_SYNC_END, val & 0x7F);
}


// ============================================================
// vgaCrtcWrite
// ============================================================

void vgaCrtcWrite(uint8_t index, uint8_t val) {
    outportb(VGA_CRTC_INDEX, index);
    outportb(VGA_CRTC_DATA, val);
}


// ============================================================
// vgaDacReadColor
// ============================================================
//
// Read one DAC palette entry. Write the index to 0x3C7, then
// read three bytes (R, G, B) from 0x3C9. DAC values are 6-bit
// (0-63) on standard VGA, 8-bit on some SVGA cards.

void vgaDacReadColor(uint8_t index, uint8_t *r, uint8_t *g, uint8_t *b) {
    outportb(VGA_DAC_READ_ADDR, index);
    *r = inportb(VGA_DAC_DATA);
    *g = inportb(VGA_DAC_DATA);
    *b = inportb(VGA_DAC_DATA);
}


// ============================================================
// vgaDacWriteColor
// ============================================================
//
// Write one DAC palette entry. Write the starting index to 0x3C8,
// then write three bytes (R, G, B) to 0x3C9.

void vgaDacWriteColor(uint8_t index, uint8_t r, uint8_t g, uint8_t b) {
    outportb(VGA_DAC_WRITE_ADDR, index);
    outportb(VGA_DAC_DATA, r);
    outportb(VGA_DAC_DATA, g);
    outportb(VGA_DAC_DATA, b);
}


// ============================================================
// vgaGfxRead
// ============================================================

uint8_t vgaGfxRead(uint8_t index) {
    outportb(VGA_GFX_INDEX, index);
    return inportb(VGA_GFX_DATA);
}


// ============================================================
// vgaGfxWrite
// ============================================================

void vgaGfxWrite(uint8_t index, uint8_t val) {
    outportb(VGA_GFX_INDEX, index);
    outportb(VGA_GFX_DATA, val);
}


// ============================================================
// vgaMiscRead
// ============================================================

uint8_t vgaMiscRead(void) {
    return inportb(VGA_MISC_OUT_R);
}


// ============================================================
// vgaMiscWrite
// ============================================================

void vgaMiscWrite(uint8_t val) {
    outportb(VGA_MISC_OUT_W, val);
}


// ============================================================
// vgaRestoreTextMode
// ============================================================
//
// Restores VGA text mode 3 (80x25, 16 color). Uses INT 10h
// because manually reprogramming all VGA registers for text mode
// is error-prone and varies by chipset. The BIOS handles it
// correctly for all VGA-compatible cards.

void vgaRestoreTextMode(void) {
    __dpmi_regs r;

    memset(&r, 0, sizeof(r));
    r.x.ax = 0x0003;
    __dpmi_int(0x10, &r);
}


// ============================================================
// vgaSeqRead
// ============================================================

uint8_t vgaSeqRead(uint8_t index) {
    outportb(VGA_SEQ_INDEX, index);
    return inportb(VGA_SEQ_DATA);
}


// ============================================================
// vgaSeqWrite
// ============================================================

void vgaSeqWrite(uint8_t index, uint8_t val) {
    outportb(VGA_SEQ_INDEX, index);
    outportb(VGA_SEQ_DATA, val);
}


// ============================================================
// vgaWaitVRetrace
// ============================================================
//
// Waits for the start of the next vertical retrace by spinning
// on bit 3 of Input Status 1 (port 0x3DA). First waits for bit
// to clear (if we're currently in retrace), then waits for it
// to set (start of next retrace).

void vgaWaitVRetrace(void) {
    // Wait for any current retrace to end
    while (inportb(VGA_INPUT_STATUS_1) & 0x08) {
        // spin
    }

    // Wait for next retrace to start
    while (!(inportb(VGA_INPUT_STATUS_1) & 0x08)) {
        // spin
    }
}