From 524439907ac49927d6310e8d4c4ec43841bc47a2 Mon Sep 17 00:00:00 2001
From: hap <happppp@users.noreply.github.com>
Date: Sat, 9 May 2020 17:15:46 +0200
Subject: [PATCH] 6801: tcsr upper 3 bits are read-only (nw)

---
 src/devices/cpu/m6800/m6801.cpp |  8 +++++---
 src/devices/cpu/m6800/m6801.h   |  3 +--
 src/mame/drivers/psion.cpp      | 15 ---------------
 src/mame/includes/psion.h       |  2 --
 4 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/src/devices/cpu/m6800/m6801.cpp b/src/devices/cpu/m6800/m6801.cpp
index e279137f86e..a2c036825f4 100644
--- a/src/devices/cpu/m6800/m6801.cpp
+++ b/src/devices/cpu/m6800/m6801.cpp
@@ -1352,10 +1352,10 @@ uint8_t hd6301x_cpu_device::p7_data_r()
 
 void hd6301x_cpu_device::p7_data_w(uint8_t data)
 {
-	LOGPORT("Port 7 Data Register: %02x\n", data);
-
 	data &= 0x1f;
 
+	LOGPORT("Port 7 Data Register: %02x\n", data);
+
 	m_portx_data[2] = data;
 	m_out_portx_func[2](0, m_portx_data[2], 0x1f);
 }
@@ -1369,9 +1369,11 @@ uint8_t m6801_cpu_device::tcsr_r()
 
 void m6801_cpu_device::tcsr_w(uint8_t data)
 {
+	data &= 0x1f;
+
 	LOGTIMER("Timer Control and Status Register: %02x\n", data);
 
-	m_tcsr = data;
+	m_tcsr = data | (m_tcsr & 0xe0);
 	m_pending_tcsr &= m_tcsr;
 	modified_tcsr();
 	if( !(m_cc & 0x10) )
diff --git a/src/devices/cpu/m6800/m6801.h b/src/devices/cpu/m6800/m6801.h
index b9d65bb9d02..ecb34ccf65a 100644
--- a/src/devices/cpu/m6800/m6801.h
+++ b/src/devices/cpu/m6800/m6801.h
@@ -91,10 +91,9 @@ protected:
 	uint8_t p4_data_r();
 	void p4_data_w(uint8_t data);
 
-public: // FIXME: psion.cpp accesses this
+protected:
 	uint8_t tcsr_r();
 	void tcsr_w(uint8_t data);
-protected:
 	uint8_t ch_r();
 	uint8_t cl_r();
 	void ch_w(uint8_t data);
diff --git a/src/mame/drivers/psion.cpp b/src/mame/drivers/psion.cpp
index 0f67945d5ff..1b941b19d11 100644
--- a/src/mame/drivers/psion.cpp
+++ b/src/mame/drivers/psion.cpp
@@ -76,19 +76,6 @@ uint8_t psion_state::port2_r()
 	return m_pack1->data_r() | m_pack2->data_r();
 }
 
-void psion_state::tcsr_w(uint8_t data)
-{
-	m_tcsr_value = data;
-	m_maincpu->tcsr_w(data);
-}
-
-uint8_t psion_state::tcsr_r()
-{
-	if (!machine().side_effects_disabled())
-		m_maincpu->tcsr_w(m_tcsr_value);
-	return m_maincpu->tcsr_r();
-}
-
 uint8_t psion_state::rcp5c_r()
 {
 	return (m_maincpu->rcr_r()&0x7f) | (m_stby_pwr<<7);
@@ -247,7 +234,6 @@ void psion_state::psion_int_reg(address_map &map)
 {
 	// FIXME: this should all be made internal to the CPU device
 	map(0x0000, 0x001f).m(m_maincpu, FUNC(hd6301x_cpu_device::hd6301x_io));
-	map(0x0008, 0x0008).rw(FUNC(psion_state::tcsr_r), FUNC(psion_state::tcsr_w));
 	map(0x0014, 0x0014).r(FUNC(psion_state::rcp5c_r));
 }
 
@@ -496,7 +482,6 @@ void psion_state::machine_start()
 
 	save_item(NAME(m_kb_counter));
 	save_item(NAME(m_enable_nmi));
-	save_item(NAME(m_tcsr_value));
 	save_item(NAME(m_stby_pwr));
 	save_item(NAME(m_pulse));
 	save_item(NAME(m_rom_bank));
diff --git a/src/mame/includes/psion.h b/src/mame/includes/psion.h
index ee852094b87..f0f6f970ae3 100644
--- a/src/mame/includes/psion.h
+++ b/src/mame/includes/psion.h
@@ -85,8 +85,6 @@ protected:
 	void update_banks();
 	void port2_w(offs_t offset, uint8_t data, uint8_t ddr);
 	uint8_t port2_r();
-	void tcsr_w(uint8_t data);
-	uint8_t tcsr_r();
 	uint8_t rcp5c_r();
 	uint8_t port5_r();
 	void port6_w(uint8_t data);