On Sun, 31 Dec 2023, Paolo Bonzini wrote:
This allows setting the start address to a high value, and reading the bottom of the screen from the beginning of VRAM. Commander Keen 4 ("Goodbye, Galaxy!") relies on this behavior.Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> --- hw/display/vga-helpers.h | 9 +++++---- hw/display/vga.c | 3 +++ 2 files changed, 8 insertions(+), 4 deletions(-) diff --git a/hw/display/vga-helpers.h b/hw/display/vga-helpers.h index 10e9cfd40a0..83b9a15604a 100644 --- a/hw/display/vga-helpers.h +++ b/hw/display/vga-helpers.h @@ -108,7 +108,7 @@ static void vga_draw_line2(VGACommonState *vga, uint8_t *d, plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf]; width >>= 3; for(x = 0; x < width; x++) { - data = vga_read_dword_le(vga, addr); + data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1)); data &= plane_mask; v = expand2[GET_PLANE(data, 0)]; v |= expand2[GET_PLANE(data, 2)] << 2; @@ -144,7 +144,7 @@ static void vga_draw_line2d2(VGACommonState *vga, uint8_t *d, plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf]; width >>= 3; for(x = 0; x < width; x++) { - data = vga_read_dword_le(vga, addr); + data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1)); data &= plane_mask; v = expand2[GET_PLANE(data, 0)]; v |= expand2[GET_PLANE(data, 2)] << 2; @@ -177,7 +177,7 @@ static void vga_draw_line4(VGACommonState *vga, uint8_t *d, plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf]; width >>= 3; for(x = 0; x < width; x++) { - data = vga_read_dword_le(vga, addr); + data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1)); data &= plane_mask; v = expand4[GET_PLANE(data, 0)]; v |= expand4[GET_PLANE(data, 1)] << 1; @@ -209,7 +209,7 @@ static void vga_draw_line4d2(VGACommonState *vga, uint8_t *d, plane_mask = mask16[vga->ar[VGA_ATC_PLANE_ENABLE] & 0xf]; width >>= 3; for(x = 0; x < width; x++) { - data = vga_read_dword_le(vga, addr); + data = vga_read_dword_le(vga, addr & (VGA_VRAM_SIZE - 1)); data &= plane_mask; v = expand4[GET_PLANE(data, 0)]; v |= expand4[GET_PLANE(data, 1)] << 1; @@ -242,6 +242,7 @@ static void vga_draw_line8d2(VGACommonState *vga, uint8_t *d, palette = vga->last_palette; width >>= 3; for(x = 0; x < width; x++) { + addr &= VGA_VRAM_SIZE - 1; PUT_PIXEL2(d, 0, palette[vga_read_byte(vga, addr + 0)]); PUT_PIXEL2(d, 1, palette[vga_read_byte(vga, addr + 1)]); PUT_PIXEL2(d, 2, palette[vga_read_byte(vga, addr + 2)]); diff --git a/hw/display/vga.c b/hw/display/vga.c index 3bd357d72c2..b1660bdde67 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -47,6 +47,9 @@ bool have_vga = true; /* 16 state changes per vertical frame @60 Hz */ #define VGA_TEXT_CURSOR_PERIOD_MS (1000 * 2 * 16 / 60) +/* Address mask for non-VESA modes. */ +#define VGA_VRAM_SIZE 262144
(256 * KiB) maybe?
+ /* * Video Graphics Array (VGA) *
