Fixes for MC68EZ328 (#13286)

* MC68EZ328: Allow selection and use of Port A

On EZ and VZ, PASEL is reserved, and it was hard-coded to 0 (disabled).
However, the user manual notes: "In an 8-bit-only system, you can
configure these pins as a parallel I/O port by writing a 1 to the
WDTH8 bit of the SCR."

According to the MC68328 datasheet, something similar should be needed
to activate its Port B, but that change is not included here. Its PBSEL
is exposed, so there is likely no difference in emulation.

* MC68EZ328: Fuller implementation of timer

The existing implementation left the timer counter (TCN) at zero until
the compare value (TCMP) was reached. However, some software relies on
reading the TCN values to measure elapsed time.

The timer counter (TCN) now increments on every timer tick.

src/devices/machine/mc68328.cpp

@@ -972,6 +972,15 @@ u16 mc68328_device::csd_lsw_r() // 0x11e, 0x12e, 0x13e, 0x14e
 //  MMU/chip-select hardware - EZ variant
 //-------------------------------------------------
 
+void mc68ez328_device::scr_w(u8 data)
+{
+	if (data & SCR_WDTH8)
+	{
+		m_pasel = 0xff;
+	}
+	mc68328_base_device::scr_w(data);
+}
+
 u8 mc68ez328_device::revision_r(offs_t offset)
 {
 	LOGMASKED(LOG_PLL, "%s: revision_r: Silicon Revision[%d] = %02x\n", machine().describe_context(), offset, 0x01);
@@ -2668,7 +2677,7 @@ void mc68328_base_device::update_gptimer_state()
 		}
 		else
 		{
-			timer->adjust(attotime::from_ticks(regs.tcmp, get_timer_frequency<Timer>()));
+			timer->adjust(attotime::from_hz(get_timer_frequency<Timer>()));
 		}
 	}
 	else
@@ -2683,40 +2692,31 @@ TIMER_CALLBACK_MEMBER(mc68328_base_device::timer_tick)
 	timer_regs &regs = get_timer_regs(Timer);
 	emu_timer *timer = get_timer(Timer);
 
-	regs.tcn = regs.tcmp;
-	regs.tstat |= TSTAT_COMP;
-
-	if ((regs.tctl & TCTL_FRR) == TCTL_FRR_RESTART)
+	u32 frequency = get_timer_frequency<Timer>();
+	if (frequency > 0)
 	{
-		u32 frequency = get_timer_frequency<Timer>();
-		if (frequency > 0)
-		{
-			attotime period = attotime::from_hz(frequency) * regs.tcmp;
-			regs.tcn = 0x0000;
-			timer->adjust(period);
-		}
-		else
-		{
-			timer->adjust(attotime::never);
-		}
+		attotime period = attotime::from_hz(frequency);
+		timer->adjust(period);
 	}
 	else
 	{
-		u32 frequency = get_timer_frequency<Timer>();
-		if (frequency > 0)
+		timer->adjust(attotime::never);
+	}
+
+	regs.tcn++;
+	if (regs.tcn == regs.tcmp)
+	{
+		regs.tstat |= TSTAT_COMP;
+		if ((regs.tctl & TCTL_FRR) == TCTL_FRR_RESTART)
 		{
-			attotime period = attotime::from_hz(frequency) * 0x10000;
-			timer->adjust(period);
+			regs.tcn = 0x0000;
 		}
-		else
+
+		if ((regs.tctl & TCTL_IRQEN) == TCTL_IRQEN_ENABLE)
 		{
-			timer->adjust(attotime::never);
+			set_interrupt_line(get_timer_int(Timer), 1);
 		}
 	}
-	if ((regs.tctl & TCTL_IRQEN) == TCTL_IRQEN_ENABLE)
-	{
-		set_interrupt_line(get_timer_int(Timer), 1);
-	}
 }
 
 template <int Timer>

src/devices/machine/mc68328.h

@@ -430,7 +430,7 @@ class mc68328_base_device : public m68000_device
 		RTCHMSR_HOURS_SHIFT     = 24,
 	};
 
-	void scr_w(u8 data);
+	virtual void scr_w(u8 data);
 
 	void grpbasea_w(u16 data);
 	void grpbaseb_w(u16 data);
@@ -1143,6 +1143,8 @@ class mc68ez328_device : public mc68328_base_device
 		INT_MEMIQ_MASK          = (1 << INT_MEMIQ),
 	};
 
+	virtual void scr_w(u8 data) override;
+
 	void csa_w(offs_t offset, u16 data, u16 mem_mask);
 	void csb_w(offs_t offset, u16 data, u16 mem_mask);
 	void csc_w(offs_t offset, u16 data, u16 mem_mask);