i8256: calculate timer from external clock

src/devices/machine/i8256.cpp

@@ -248,7 +248,18 @@ void i8256_device::device_reset()
 
 	m_status = 0x30; // TRE and TBE
 
-	m_timer->adjust(attotime::from_hz(16000), 0, attotime::from_hz(16000));
+	reset_timer();
+}
+
+void i8256_device::reset_timer()
+{
+	int divider = 64; //default is 16kHz from the datasheet, it may later be changed to a slower one
+	if (BIT(m_command1, I8256_CMD1_FRQ))
+	{
+		divider = 1024;
+	}
+	const attotime time = attotime::from_hz((clock() / SYS_CLOCK_DIVIDER[(m_command2 & 0x30 >> 4)]) / divider);
+	m_timer->adjust(time, 0, time);
 }
 
 TIMER_CALLBACK_MEMBER(i8256_device::timer_check)
@@ -261,9 +272,13 @@ TIMER_CALLBACK_MEMBER(i8256_device::timer_check)
 			if (m_timers[i] == 0 && BIT(m_interrupts,timer_interrupt[i])) // If the interrupt is enabled
 			{
 				m_current_interrupt_level = timer_interrupt[i];
-				m_out_int_cb(1); // it occurs when the counter changes from 1 to 0.
+				m_out_int_cb(ASSERT_LINE); // it occurs when the counter changes from 1 to 0.
 			}
 		}
+		else
+		{
+			m_out_int_cb(CLEAR_LINE);
+		}
 	}
 }
 
@@ -335,10 +350,7 @@ void i8256_device::write(offs_t offset, u8 data)
 			{
 				m_command1 = data;
 
-				if (BIT(m_command1,I8256_CMD1_FRQ))
-					m_timer->adjust(attotime::from_hz(1000), 0, attotime::from_hz(1000));
-				else
-					m_timer->adjust(attotime::from_hz(16000), 0, attotime::from_hz(16000));
+				reset_timer();
 
 				if (BIT(m_command1,I8256_CMD1_8086))
 					LOG("I8256 Enabled 8086 mode\n");
@@ -621,7 +633,7 @@ void i8256_device::receive_character(uint8_t ch)
 {
 	LOG("I8256: receive_character %02x\n", ch);
 
-	m_rx_data = ch;
+	m_rx_buffer = ch;
 
 	LOG("status RX READY test %02x\n", m_status);
 	// char has not been read and another has arrived!

src/devices/machine/i8256.h

@@ -112,6 +112,7 @@ class i8256_device : public device_t, public device_serial_interface
 
 	TIMER_CALLBACK_MEMBER(timer_check);
 
+	void reset_timer();
 	void receive_clock();
 	void sync1_rxc();
 	void sync2_rxc();