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mc6845: address cursor display edge case in interlaced mode.

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It appears that the cursor is not displayed when the start raster
address is equal to the maximum raster address in the 'interlace and
video' mode. At least this addresses a claimed regression in the
'apricot' machine. To be explore further on hardware.

The maximum raster address was also off by one in these calculations.
This commit is contained in:
68bit 2019-08-29 14:28:12 +10:00
parent cbb3262e2a
commit 70f62a1c07
1 changed files with 9 additions and 1 deletions
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10
src/devices/video/mc6845.cpp
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@ -705,7 +705,7 @@ 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);
uint16_t max_ras_addr = m_max_ras_addr + (MODE_INTERLACE_AND_VIDEO ? m_interlace_adjust : m_noninterlace_adjust) - 1;
if (cursor_start_ras > max_ras_addr)
{
@ -713,6 +713,14 @@ bool mc6845_device::check_cursor_visible(uint16_t ra, uint16_t line_addr)
return false;
}
// See the 'apricot' boot screen, it probably expects no cursor.
// TODO explore the edge cases in the 'interlace and video' mode.
if (MODE_INTERLACE_AND_VIDEO && cursor_start_ras >= max_ras_addr)
{
// No cursor possible.
return false;
}
if (cursor_start_ras <= m_cursor_end_ras)
{
if (m_cursor_end_ras > max_ras_addr)