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i8275: Continue DMA bursts when display is stopped (nw)

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This commit is contained in:
AJR 2019-07-01 10:34:50 -04:00
parent 491107e78d
commit 1b4109e817
1 changed files with 15 additions and 17 deletions
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14
src/devices/video/i8275.cpp
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@ -209,14 +209,15 @@ void i8275_device::vrtc_start()
//LOG("I8275 y %u x %u VRTC 1\n", y, x);
m_write_vrtc(1);
if (m_status & ST_VE)
{
// reset field attributes
m_field_attr = 0;
// Intel datasheets imply DMA requests begin only after a "Start Display" command is issued.
// WY-100, however, expects a BRDY cycle from the 8276 after the program first configures and stops the display.
// This suggests that DMA bursts proceed as normal in this case, but any characters sent will not be displayed.
m_buffer_idx = CHARACTERS_PER_ROW;
m_dma_stop = false;
m_end_of_screen = false;
m_end_of_screen = !(m_status & ST_VE);
m_cursor_blink++;
m_cursor_blink &= 0x1f;
@ -225,7 +226,6 @@ void i8275_device::vrtc_start()
m_char_blink &= 0x3f;
m_stored_attr = 0;
}
}
//-------------------------------------------------
@ -285,7 +285,7 @@ void i8275_device::device_timer(emu_timer &timer, device_timer_id id, int param,
if (m_scanline == 0)
vrtc_end();
if ((m_status & ST_VE) && lc == 0 && m_scanline < m_vrtc_scanline)
if (lc == 0 && m_scanline < m_vrtc_scanline)
{
if (!m_dma_stop && m_buffer_idx < CHARACTERS_PER_ROW)
{
@ -320,7 +320,7 @@ void i8275_device::device_timer(emu_timer &timer, device_timer_id id, int param,
if (m_scanline == m_vrtc_scanline)
vrtc_start();
if ((m_status & ST_VE) && m_scanline == m_vrtc_drq_scanline)
if (!m_dma_stop && m_scanline == m_vrtc_drq_scanline)
{
// swap line buffers
m_buffer_dma = !m_buffer_dma;
@ -609,9 +609,7 @@ WRITE8_MEMBER( i8275_device::write )
m_param[m_param_idx] = data;
if (m_param_idx == REG_SCN4)
{
recompute_parameters();
}
m_param_idx++;
}