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i8251: added bisync support

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This commit is contained in:
Robbbert 2019-09-08 22:51:05 +10:00
parent fde41f3fad
commit 4e63fc410b
1 changed files with 51 additions and 2 deletions
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53
src/devices/machine/i8251.cpp
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@ -233,8 +233,57 @@ void i8251_device::sync2_rxc()
if (m_syndet_pin && !m_ext_syn_set)
return;
// remainder yet to be written
(void)m_sync2;
u8 need_parity = BIT(m_mode_byte, 4);
// see about parity
if (need_parity && (m_rxd_bits == m_data_bits_count))
{
if (calc_parity(m_sync1) != m_rxd)
m_status |= I8251_STATUS_PARITY_ERROR;
// and then continue on as if everything was ok
}
else
{
// add bit to byte
m_sync1 = (m_sync1 >> 1) | (m_rxd << (m_data_bits_count-1));
m_sync2 = (m_sync2 >> 1) | (m_rxd << (m_data_bits_count*2-1));
}
// if we are in hunt mode, the byte loaded has to
// be the sync byte. If not, go around again.
// if we leave hunt mode now, the sync byte must not go to the receive buffer
bool was_in_hunt_mode = false;
if (m_hunt_on)
{
if (m_sync2 == m_sync16)
{
m_rxd_bits = m_data_bits_count;
m_hunt_on = false;
was_in_hunt_mode = true;
}
else
return;
}
// is byte complete? if not, quit
m_rxd_bits++;
if (m_rxd_bits < (m_data_bits_count + need_parity))
return;
// now we have a synchronised byte, and parity has been dealt with
// copy byte to rx buffer
if (!was_in_hunt_mode)
receive_character(m_sync1);
// Is it a sync byte? syndet gets indicated whenever
// a sync byte passes by, regardless of hunt_mode status.
if (m_sync2 == m_sync16)
update_syndet(true);
m_rxd_bits = 0;
m_sync1 = 0;
m_sync2 = 0;
}
/*-------------------------------------------------