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MC6845: correct cursor.

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The MC6845 shows a full cursor if the cursor end raster address is
greater than the maximum raster address, restore that case in general.

The issue on the BBC, that uses the HD6845S, might be the use of the
maximum raster address here, it appears to be programmed differently
on the HD6845S and also to depend on the interlaced mode. This patch
fixes the BBC while preserving the cursor emulation for the MC6845.
This commit is contained in:
68bit 2019-08-28 10:23:16 +10:00
parent d6c145c0e7
commit 912a1c1b9d
1 changed files with 7 additions and 1 deletions
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8
src/devices/video/mc6845.cpp
View File

@ -705,8 +705,9 @@ bool mc6845_device::check_cursor_visible(uint16_t ra, uint16_t line_addr)
}
uint16_t cursor_start_ras = m_cursor_start_ras & 0x1f;
uint16_t max_ras_addr = m_max_ras_addr + (MODE_INTERLACE_AND_VIDEO ? m_interlace_adjust : m_noninterlace_adjust);
if (cursor_start_ras > m_max_ras_addr)
if (cursor_start_ras > max_ras_addr)
{
// No cursor possible.
return false;
@ -714,6 +715,11 @@ bool mc6845_device::check_cursor_visible(uint16_t ra, uint16_t line_addr)
if (cursor_start_ras <= m_cursor_end_ras)
{
if (m_cursor_end_ras > max_ras_addr)
{
// Full cursor.
return true;
}
// Cursor from start to end inclusive.
return (ra >= cursor_start_ras) && (ra <= m_cursor_end_ras);
}