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emu/diserial.cpp: Improved stop bit handling (fixes #12762). (#12770)

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* Never check more than one stop bit on reception.
* Don't add an extra stop bit on transmission.
This commit is contained in:
Colin Leroy-Mira 2024-09-22 17:57:25 +02:00 committed by GitHub
parent bd873d2c62
commit afab68e6c2
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GPG Key ID: B5690EEEBB952194
2 changed files with 19 additions and 7 deletions
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22
src/emu/diserial.cpp
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@ -25,6 +25,7 @@ device_serial_interface::device_serial_interface(const machine_config &mconfig,
m_df_word_length(0),
m_df_parity(PARITY_NONE),
m_df_stop_bit_count(STOP_BITS_0),
m_df_min_rx_stop_bit_count(0),
m_rcv_register_data(0x8000),
m_rcv_flags(0),
m_rcv_bit_count_received(0),
@ -81,6 +82,7 @@ void device_serial_interface::interface_post_start()
device().save_item(NAME(m_df_word_length));
device().save_item(NAME(m_df_parity));
device().save_item(NAME(m_df_stop_bit_count));
device().save_item(NAME(m_df_min_rx_stop_bit_count));
device().save_item(NAME(m_rcv_register_data));
device().save_item(NAME(m_rcv_flags));
device().save_item(NAME(m_rcv_bit_count_received));
@ -174,25 +176,30 @@ void device_serial_interface::set_data_frame(int start_bit_count, int data_bit_c
case STOP_BITS_0:
default:
m_df_stop_bit_count = 0;
m_df_min_rx_stop_bit_count = 0;
break;
case STOP_BITS_1:
m_df_stop_bit_count = 1;
m_df_min_rx_stop_bit_count = 1;
break;
case STOP_BITS_1_5:
m_df_stop_bit_count = 2; // TODO: support 1.5 stop bits
m_df_min_rx_stop_bit_count = 1;
break;
case STOP_BITS_2:
m_df_stop_bit_count = 2;
m_df_min_rx_stop_bit_count = 1;
break;
}
m_df_parity = parity;
m_df_start_bit_count = start_bit_count;
m_rcv_bit_count = m_df_word_length + m_df_stop_bit_count;
/* Require at least one stop bit in async RX mode, none in sync RX mode. */
m_rcv_bit_count = m_df_word_length + m_df_min_rx_stop_bit_count;
if (m_df_parity != PARITY_NONE)
{
@ -274,6 +281,10 @@ void device_serial_interface::receive_register_update_bit(int bit)
m_rcv_framing_error = false;
m_rcv_parity_error = false;
}
else
{
LOGMASKED(LOG_RX, "Receiver saw stop bit (%s)\n", device().machine().time().to_string());
}
}
}
else if (m_rcv_flags & RECEIVE_REGISTER_SYNCHRONISED)
@ -281,7 +292,7 @@ void device_serial_interface::receive_register_update_bit(int bit)
LOGMASKED(LOG_RX, "Received bit %d as %d (%s)\n", m_rcv_bit_count_received, bit, device().machine().time().to_string());
m_rcv_bit_count_received++;
if (!bit && (m_rcv_bit_count_received > (m_rcv_bit_count - m_df_stop_bit_count)))
if (!bit && (m_rcv_bit_count_received > (m_rcv_bit_count - m_df_min_rx_stop_bit_count)))
{
LOGMASKED(LOG_RX, "Framing error\n");
m_rcv_framing_error = true;
@ -424,10 +435,9 @@ void device_serial_interface::transmit_register_setup(u8 data_byte)
transmit_register_add_bit(parity);
}
/* stop bit(s) + 1 extra bit as delay between bytes, needed to get 1 stop bit to work. */
if (m_df_stop_bit_count) // no stop bits for synchronous
for (i=0; i<=m_df_stop_bit_count; i++) // ToDo - see if the hack on this line is still needed (was added 2016-04-10)
transmit_register_add_bit(1);
/* TX stop bit(s) */
for (i=0; i<m_df_stop_bit_count; i++)
transmit_register_add_bit(1);
}

4
src/emu/diserial.h
View File

@ -141,8 +141,10 @@ private:
u8 m_df_word_length;
// parity state
u8 m_df_parity;
// number of stop bits
// number of TX stop bits
u8 m_df_stop_bit_count;
// min. number of RX stop bits
u8 m_df_min_rx_stop_bit_count;
// Receive register
/* data */