nvram: don't save 0byte file (nw)

src/devices/machine/nvram.h

@@ -57,6 +57,7 @@ protected:
 	virtual void nvram_default() override;
 	virtual void nvram_read(emu_file &file) override;
 	virtual void nvram_write(emu_file &file) override;
+	virtual bool nvram_pre_write() override { return m_base && m_length; }
 
 	// internal helpers
 	void determine_final_base();

src/devices/machine/rp5c01.h

@@ -65,6 +65,7 @@ protected:
 	virtual void nvram_default() override;
 	virtual void nvram_read(emu_file &file) override;
 	virtual void nvram_write(emu_file &file) override;
+	virtual bool nvram_pre_write() override { return m_battery_backed; }
 
 private:
 	inline void set_alarm_line();

src/devices/machine/sensorboard.cpp

@@ -67,7 +67,7 @@ DEFINE_DEVICE_TYPE(SENSORBOARD, sensorboard_device, "sensorboard", "Sensorboard"
 
 sensorboard_device::sensorboard_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock) :
 	device_t(mconfig, SENSORBOARD, tag, owner, clock),
-	m_nvram(*this, "position"),
+	device_nvram_interface(mconfig, *this),
 	m_out_piece(*this, "piece_%c%u", 0U + 'a', 1U),
 	m_out_pui(*this, "piece_ui%u", 0U),
 	m_out_count(*this, "count_ui%u", 0U),
@@ -127,8 +127,6 @@ void sensorboard_device::device_start()
 	m_ulast = 0;
 	m_usize = ARRAY_LENGTH(m_history);
 
-	m_nvram->set_base(m_curstate, sizeof(m_curstate));
-
 	// register for savestates
 	save_item(NAME(m_magnets));
 	save_item(NAME(m_inductive));
@@ -155,18 +153,6 @@ void sensorboard_device::device_start()
 	save_item(NAME(m_sensordelay));
 }
 
-void sensorboard_device::nvram_init(nvram_device &nvram, void *data, size_t size)
-{
-	clear_board();
-	m_custom_init_cb(1);
-}
-
-void sensorboard_device::device_add_mconfig(machine_config &config)
-{
-	// 'nvram' is the last board position (m_curstate)
-	NVRAM(config, m_nvram).set_custom_handler(FUNC(sensorboard_device::nvram_init));
-}
-
 void sensorboard_device::preset_chess(int state)
 {
 	// set chessboard start position
@@ -214,6 +200,32 @@ void sensorboard_device::device_reset()
 }
 
 
+//-------------------------------------------------
+//  device_nvram_interface overrides
+//-------------------------------------------------
+
+void sensorboard_device::nvram_default()
+{
+	clear_board();
+	m_custom_init_cb(1);
+}
+
+void sensorboard_device::nvram_read(emu_file &file)
+{
+	file.read(m_curstate, sizeof(m_curstate));
+}
+
+void sensorboard_device::nvram_write(emu_file &file)
+{
+	file.write(m_curstate, sizeof(m_curstate));
+}
+
+bool sensorboard_device::nvram_pre_write()
+{
+	return m_nvram_on;
+}
+
+
 
 //-------------------------------------------------
 //  public handlers

src/devices/machine/sensorboard.h

@@ -11,10 +11,7 @@
 
 #pragma once
 
-#include "machine/nvram.h"
+class sensorboard_device : public device_t, public device_nvram_interface
-
-
-class sensorboard_device : public device_t
 {
 public:
 	sensorboard_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock = 0);
@@ -81,13 +78,17 @@ protected:
 	// device-level overrides
 	virtual void device_start() override;
 	virtual void device_reset() override;
-	virtual void device_add_mconfig(machine_config &config) override;
 	virtual void device_post_load() override { refresh(); }
 
 	virtual ioport_constructor device_input_ports() const override;
 
+	// device_nvram_interface overrides
+	virtual void nvram_default() override;
+	virtual void nvram_read(emu_file &file) override;
+	virtual void nvram_write(emu_file &file) override;
+	virtual bool nvram_pre_write() override;
+
 private:
-	required_device<nvram_device> m_nvram;
 	output_finder<0x10, 0x10> m_out_piece;
 	output_finder<0x20+1> m_out_pui;
 	output_finder<2> m_out_count;
@@ -114,6 +115,7 @@ private:
 	int m_droppos;
 	int m_sensorpos;
 	u8 m_ui_enabled;
+	bool m_nvram_on;
 
 	u8 m_curstate[0x100];
 	u8 m_history[1000][0x100];
@@ -124,9 +126,6 @@ private:
 	u32 m_ulast;
 	u32 m_usize;
 
-	void nvram_init(nvram_device &nvram, void *data, size_t size);
-	bool m_nvram_on;
-
 	emu_timer *m_undotimer;
 	TIMER_CALLBACK_MEMBER(undo_tick);
 	void undo_reset();

src/emu/dinvram.h

@@ -37,12 +37,14 @@ public:
 	void nvram_reset() { nvram_default(); }
 	void nvram_load(emu_file &file) { nvram_read(file); }
 	void nvram_save(emu_file &file) { nvram_write(file); }
+	bool nvram_pre_save() { return nvram_pre_write(); }
 
 protected:
 	// derived class overrides
 	virtual void nvram_default() = 0;
 	virtual void nvram_read(emu_file &file) = 0;
 	virtual void nvram_write(emu_file &file) = 0;
+	virtual bool nvram_pre_write() { return true; }
 };
 
 // iterator

src/emu/machine.cpp

@@ -1203,11 +1203,14 @@ void running_machine::nvram_save()
 {
 	for (device_nvram_interface &nvram : nvram_interface_iterator(root_device()))
 	{
-		emu_file file(options().nvram_directory(), OPEN_FLAG_WRITE | OPEN_FLAG_CREATE | OPEN_FLAG_CREATE_PATHS);
+		if (nvram.nvram_pre_save())
-		if (file.open(nvram_filename(nvram.device())) == osd_file::error::NONE)
 		{
-			nvram.nvram_save(file);
+			emu_file file(options().nvram_directory(), OPEN_FLAG_WRITE | OPEN_FLAG_CREATE | OPEN_FLAG_CREATE_PATHS);
-			file.close();
+			if (file.open(nvram_filename(nvram.device())) == osd_file::error::NONE)
+			{
+				nvram.nvram_save(file);
+				file.close();
+			}
 		}
 	}
 }