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authorGravatarGravatar R. Belmont <rb6502@users.noreply.github.com>2014-01-10 03:09:04 +0000
committerGravatarGravatar R. Belmont <rb6502@users.noreply.github.com>2014-01-10 03:09:04 +0000
commit0c310baef57efe3e7405026516cd139bfffddec8 (patch)
treed7e673066e30b6aad3833af59eeae8fad459daaf /src
parent14cd942836a5831a047403fb4fdf4ecceb548653 (diff)
i8251: as per the manual, disabling Tx mid-byte should wait for transmission to finish [R. Belmont]
Diffstat (limited to 'src')
-rw-r--r--src/emu/machine/i8251.c59
-rw-r--r--src/emu/machine/i8251.h1
2 files changed, 45 insertions, 15 deletions
diff --git a/src/emu/machine/i8251.c b/src/emu/machine/i8251.c
index 3e2f3ff5163..8e8edc39164 100644
--- a/src/emu/machine/i8251.c
+++ b/src/emu/machine/i8251.c
@@ -172,13 +172,13 @@ void i8251_device::transmit_clock()
else
return;
- /* transmit enable? */
+ /* transmit enabled? */
if (m_command & (1<<0))
{
- /* transmit register full? */
+ /* do we have a character to send? */
if ((m_status & I8251_STATUS_TX_READY)==0)
{
- /* if transmit reg is empty */
+ /* is diserial ready for it? */
if (is_transmit_register_empty())
{
/* set it up */
@@ -193,18 +193,32 @@ void i8251_device::transmit_clock()
}
}
- /* if transmit is not empty... transmit data */
+ /* if diserial has bits to send, make them so */
if (!is_transmit_register_empty())
{
UINT8 data = transmit_register_get_data_bit();
- // logerror("I8251\n");
- //transmit_register_send_bit();
+ m_tx_busy = true;
m_out_txd_func(data);
m_connection_state &= ~TX;
m_connection_state|=(data<<5);
serial_connection_out();
}
+
+ // is transmitter totally done?
+ if ((m_status & I8251_STATUS_TX_READY) && is_transmit_register_empty())
+ {
+ m_tx_busy = false;
+
+ if (m_disable_tx_pending)
+ {
+ LOG(("Applying pending disable\n"));
+ m_disable_tx_pending = false;
+ m_command &= ~(1<<0);
+ set_out_data_bit(1);
+ update_tx_ready();
+ }
+ }
}
#if 0
@@ -325,6 +339,7 @@ void i8251_device::device_reset()
m_data = 0;
m_rxc = m_txc = 0;
m_br_factor = 1;
+ m_tx_busy = m_disable_tx_pending = false;
/* update tx empty pin output */
update_tx_empty();
@@ -584,10 +599,30 @@ WRITE8_MEMBER(i8251_device::control_w)
if (data & (1<<0))
{
LOG(("transmit enable\n"));
+
+ /* if we get a tx enable with a disable pending, cancel the disable */
+ m_disable_tx_pending = false;
}
else
{
- LOG(("transmit disable\n"));
+ if (m_tx_busy)
+ {
+ if (!m_disable_tx_pending)
+ {
+ LOG(("Tx busy, set pending disable\n"));
+ }
+ m_disable_tx_pending = true;
+ m_command |= (1<<0);
+ }
+ else
+ {
+ LOG(("transmit disable\n"));
+ if ((data & (1<<0))==0)
+ {
+ /* held in high state when transmit disable */
+ set_out_data_bit(1);
+ }
+ }
}
@@ -630,12 +665,6 @@ WRITE8_MEMBER(i8251_device::control_w)
m_connection_state |= DTR;
}
- if ((data & (1<<0))==0)
- {
- /* held in high state when transmit disable */
- set_out_data_bit(1);
- }
-
/* refresh outputs */
serial_connection_out();
@@ -684,7 +713,7 @@ WRITE8_MEMBER(i8251_device::data_w)
{
m_data = data;
- //logerror("write data: %02x\n",data);
+// printf("i8251 transmit char: %02x\n",data);
/* writing clears */
m_status &=~I8251_STATUS_TX_READY;
@@ -705,7 +734,7 @@ WRITE8_MEMBER(i8251_device::data_w)
void i8251_device::receive_character(UINT8 ch)
{
- //logerror("i8251 receive char: %02x\n",ch);
+// printf("i8251 receive char: %02x\n",ch);
m_data = ch;
diff --git a/src/emu/machine/i8251.h b/src/emu/machine/i8251.h
index 2cc953e9135..7213b27b922 100644
--- a/src/emu/machine/i8251.h
+++ b/src/emu/machine/i8251.h
@@ -129,6 +129,7 @@ private:
/* data being received */
UINT8 m_data;
+ bool m_tx_busy, m_disable_tx_pending;
};
// device type definition