One of the first things I noticed when I tried OpenBSD in VirtualBox was that doing ctrl-alt-2, then ctrl-alt-1 to switch back and forth between virtual screens left the text mode background a dim red color instead of black.
Here is someone else noting it, ten years ago: http://daemonforums.org/showthread.php?t=4704 It doesn't happen on a real (nvidia) VGA, but unexpected behavior on a virtual machine can be a sign that code is doing undefined things on the hardware, which is worth investigating. The call to vga_enable() at the end of vga_restore_palette() is what triggers the behavior. This appears to be truly ancient code, but I don't think it was ever correct. #define vga_enable(vh) \ vga_raw_write(vh, 0, 0x20); After resetting the attribute flip-flop, this is just setting the VGA attribute index to an illegal register value -- there aren't 32 attribute registers. The palette code doesn't even touch the attributes, so it doesn't have to reset the flip-flop, either. The vga_enable() was also used, along with another unnecessary flip flop reset (it toggles between address and data, so after writing an address and data, it is back where it started), in the vga_attr_read and write functions. Removing all this appears to work fine on both VirtualBox and Nvidia. Perhaps there was errant code that wrote to the io port register at some point, and having it dissapear into an "invalid" register hid another bug? Index: vga.c =================================================================== RCS file: /cvs/src/sys/dev/ic/vga.c,v retrieving revision 1.69 diff -u -p -r1.69 vga.c --- vga.c 17 Jun 2017 19:20:30 -0000 1.69 +++ vga.c 15 May 2020 23:38:32 -0000 @@ -1213,8 +1213,6 @@ vga_save_palette(struct vga_config *vc) vga_raw_write(vh, VGA_DAC_READ, 0x00); for (i = 0; i < 3 * 256; i++) *palette++ = vga_raw_read(vh, VGA_DAC_DATA); - - vga_raw_read(vh, 0x0a); /* reset flip/flop */ } void @@ -1231,10 +1229,6 @@ vga_restore_palette(struct vga_config *v vga_raw_write(vh, VGA_DAC_WRITE, 0x00); for (i = 0; i < 3 * 256; i++) vga_raw_write(vh, VGA_DAC_DATA, *palette++); - - vga_raw_read(vh, 0x0a); /* reset flip/flop */ - - vga_enable(vh); } void Index: vgavar.h =================================================================== RCS file: /cvs/src/sys/dev/ic/vgavar.h,v retrieving revision 1.13 diff -u -p -r1.13 vgavar.h --- vgavar.h 26 Jul 2015 03:17:07 -0000 1.13 +++ vgavar.h 15 May 2020 23:38:32 -0000 @@ -96,9 +96,6 @@ static inline void _vga_gdc_write(struct #define vga_raw_write(vh, reg, value) \ bus_space_write_1(vh->vh_iot, vh->vh_ioh_vga, reg, value) -#define vga_enable(vh) \ - vga_raw_write(vh, 0, 0x20); - static inline u_int8_t _vga_attr_read(struct vga_handle *vh, int reg) { @@ -110,11 +107,6 @@ _vga_attr_read(struct vga_handle *vh, in vga_raw_write(vh, VGA_ATC_INDEX, reg); res = vga_raw_read(vh, VGA_ATC_DATAR); - /* reset state XXX unneeded? */ - (void) bus_space_read_1(vh->vh_iot, vh->vh_ioh_6845, 10); - - vga_enable(vh); - return (res); } @@ -126,11 +118,6 @@ _vga_attr_write(struct vga_handle *vh, i vga_raw_write(vh, VGA_ATC_INDEX, reg); vga_raw_write(vh, VGA_ATC_DATAW, val); - - /* reset state XXX unneeded? */ - (void) bus_space_read_1(vh->vh_iot, vh->vh_ioh_6845, 10); - - vga_enable(vh); } static inline u_int8_t
