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ussr/ms6102.cpp: Hardware-accurate descrambling of character generator using PROM data

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This commit is contained in:
AJR 2024-01-20 23:44:44 -05:00
parent 2d03bccbe8
commit df5061de51
1 changed files with 10 additions and 31 deletions
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41
src/mame/ussr/ms6102.cpp
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@ -76,6 +76,7 @@ public:
, m_crtc1(*this, "i8275_1")
, m_crtc2(*this, "i8275_2")
, m_p_chargen(*this, "chargen")
, m_p_charmap(*this, "charmap")
{ }
void ms6102(machine_config &config);
@ -125,6 +126,7 @@ private:
required_device<i8275_device> m_crtc1;
required_device<i8275_device> m_crtc2;
required_region_ptr<u8> m_p_chargen;
required_region_ptr<u8> m_p_charmap;
};
void ms6102_state::ms6102_mem(address_map &map)
@ -155,7 +157,7 @@ static const gfx_layout ms6102_charlayout =
1,
{ 0 },
{ STEP8(1,1) },
{ 0*8, 1*8, 2*8, 3*8, 4*8, 5*8, 6*8, 7*8, 8*8, 9*8, 10*8, 11*8 },
{ 1*8, 2*8, 3*8, 4*8, 5*8, 6*8, 7*8, 8*8, 9*8, 10*8, 11*8, 12*8 },
16*8
};
@ -273,36 +275,13 @@ void ms6102_state::machine_start()
m_pic->etlg_w(1);
// rearrange the chargen to be easier for us to access
int i,j;
for (i = 0; i < 0x100; i++)
for (j = 0; j < 2; j++)
m_p_chargen[0x1800+i*8+j+6] = m_p_chargen[0x1000+i*8+j];
for (i = 0; i < 0x100; i++)
for (j = 2; j < 8; j++)
m_p_chargen[0x1800+i*8+j-2] = m_p_chargen[0x1000+i*8+j];
// since we don't know which codes are for the russian symbols, give each unused char a unique marker
for (i = 0; i < 256; i++)
m_p_chargen[i*16] = i;
// copy over the ascii chars into their new positions (lines 0-7)
for (i = 0x20; i < 0x80; i++)
for (j = 0; j < 8; j++)
m_p_chargen[i*16+j+1] = m_p_chargen[0x1800+i*8+j];
// copy the russian symbols to codes 0xc0-0xff for now
for (i = 0xc0; i < 0x100; i++)
for (j = 0; j < 8; j++)
m_p_chargen[i*16+j+1] = m_p_chargen[0x1800+i*8+j];
// for punctuation, get the last 4 lines into place
for (i = 0x20; i < 0x40; i++)
for (j = 0; j < 4; j++)
m_p_chargen[i*16+8+j+1] = m_p_chargen[0x1700+i*8+j];
// for letters, get the last 4 lines into place
for (i = 0x40; i < 0x80; i++)
for (j = 0; j < 4; j++)
m_p_chargen[i*16+8+j+1] = m_p_chargen[0x1a00+i*8+j];
// for russian, get the last 4 lines into place
for (i = 0xc0; i < 0x100; i++)
for (j = 0; j < 4; j++)
m_p_chargen[i*16+8+j+1] = m_p_chargen[0x1604+i*8+j];
for (int i = 0; i < 0x40; i++)
{
const uint8_t *srcp = &m_p_chargen[0x1000 | bitswap<3>(m_p_charmap[i], 0, 1, 2) << 8 | (m_p_charmap[i] & 8) >> 1 | (i & 0x01) << 1];
uint8_t *dstp = &m_p_chargen[(i & 0x38) << 6 | (i & 0x07) << 1];
for (int j = 0; j < 0x20; j++)
std::copy_n(srcp + j * 8, 2, dstp + j * 16);
}
}