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https://github.com/holub/mame
synced 2025-07-04 01:18:59 +03:00
i8155: Make timer more efficient by not counting each cycle
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AJR
parent
b20ba46fc7
commit
a9e8be4d67
@ -109,11 +109,22 @@ enum
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// INLINE HELPERS
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//**************************************************************************
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inline uint8_t i8155_device::get_timer_mode()
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inline uint8_t i8155_device::get_timer_mode() const
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{
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return (m_count_loaded >> 8) & TIMER_MODE_MASK;
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}
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inline uint16_t i8155_device::get_timer_count() const
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{
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if (m_timer->enabled())
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{
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// timer counts down by twos
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return std::min((uint16_t(attotime_to_clocks(m_timer->remaining())) + 1) << 1, m_count_loaded & 0x3ffe) | (m_count_even_phase ? 0 : 1);
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}
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else
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return m_count_length;
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}
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inline void i8155_device::timer_output(int to)
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{
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if (to == m_to)
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@ -128,7 +139,12 @@ inline void i8155_device::timer_output(int to)
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inline void i8155_device::timer_stop_count()
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{
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// stop counting
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m_timer->enable(0);
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if (m_timer->enabled())
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{
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m_count_loaded = (m_count_loaded & (TIMER_MODE_MASK << 8)) | get_timer_count();
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m_timer->enable(false);
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}
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m_timer_tc->enable(false);
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// clear timer output
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timer_output(1);
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@ -146,11 +162,10 @@ inline void i8155_device::timer_reload_count()
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}
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// begin the odd half of the count, with one extra cycle if count is odd
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m_counter = (m_count_loaded & 0x3ffe) | 1;
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m_count_extra = BIT(m_count_loaded, 0);
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m_count_even_phase = false;
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// set up our timer
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m_timer->adjust(attotime::zero, 0, clocks_to_attotime(1));
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m_timer->adjust(clocks_to_attotime(((m_count_length & 0x3ffe) >> 1) + (m_count_length & 1)));
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timer_output(1);
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switch (get_timer_mode())
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@ -271,9 +286,8 @@ i8155_device::i8155_device(const machine_config &mconfig, device_type type, cons
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m_status(0),
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m_count_length(0),
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m_count_loaded(0),
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m_counter(0),
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m_count_extra(false),
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m_to(0)
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m_to(0),
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m_count_even_phase(false)
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{
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}
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@ -307,7 +321,8 @@ void i8155_device::device_start()
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m_ram = make_unique_clear<uint8_t[]>(256);
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// allocate timers
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m_timer = timer_alloc();
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m_timer = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(i8155_device::timer_half_counted), this));
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m_timer_tc = machine().scheduler().timer_alloc(timer_expired_delegate(FUNC(i8155_device::timer_tc), this));
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// register for state saving
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save_item(NAME(m_io_m));
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@ -318,8 +333,6 @@ void i8155_device::device_start()
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save_pointer(NAME(m_ram), 256);
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save_item(NAME(m_count_length));
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save_item(NAME(m_count_loaded));
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save_item(NAME(m_count_extra));
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save_item(NAME(m_counter));
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save_item(NAME(m_to));
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}
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@ -347,45 +360,15 @@ void i8155_device::device_reset()
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//-------------------------------------------------
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// device_timer - handler timer events
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// timer_half_counted - handler timer events
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//-------------------------------------------------
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void i8155_device::device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr)
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TIMER_CALLBACK_MEMBER(i8155_device::timer_half_counted)
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{
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if (m_count_extra)
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{
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m_count_extra = false;
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return;
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}
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// count down by twos
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m_counter -= 2;
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if (m_counter == 1)
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{
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LOGMASKED(LOG_TIMER, "Timer count half finished\n");
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// reload the even half of the count
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m_counter = m_count_loaded & 0x3ffe;
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// square wave modes produce a low output in the second half of the counting period
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if ((get_timer_mode() & TIMER_MODE_TC_PULSE) == 0)
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timer_output(0);
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}
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else if (m_counter == 2)
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{
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if ((get_timer_mode() & TIMER_MODE_TC_PULSE) != 0)
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{
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// pulse low on TC being reached
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timer_output(0);
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}
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// set timer flag
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m_status |= STATUS_TIMER;
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}
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else if (m_counter == 0)
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if (m_count_even_phase)
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{
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timer_output(1);
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m_count_even_phase = false;
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if ((get_timer_mode() & TIMER_MODE_AUTO_RELOAD) == 0 || (m_command & COMMAND_TM_MASK) == COMMAND_TM_STOP_AFTER_TC)
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{
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@ -399,6 +382,37 @@ void i8155_device::device_timer(emu_timer &timer, device_timer_id id, int param,
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timer_reload_count();
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}
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}
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else
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{
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LOGMASKED(LOG_TIMER, "Timer count half finished\n");
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// reload the even half of the count
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m_timer->adjust(clocks_to_attotime((m_count_loaded & 0x3ffe) >> 1));
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m_count_even_phase = true;
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// square wave modes produce a low output in the second half of the counting period
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if ((get_timer_mode() & TIMER_MODE_TC_PULSE) == 0)
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timer_output(0);
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else
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m_timer_tc->adjust(clocks_to_attotime((std::max(m_count_loaded & 0x3ffe, 2) - 2) >> 1));
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}
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}
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//-------------------------------------------------
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// timer_tc - generate TC low pulse
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//-------------------------------------------------
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TIMER_CALLBACK_MEMBER(i8155_device::timer_tc)
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{
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if ((get_timer_mode() & TIMER_MODE_TC_PULSE) != 0)
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{
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// pulse low on TC being reached
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timer_output(0);
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}
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// set timer flag
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m_status |= STATUS_TIMER;
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}
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@ -416,7 +430,8 @@ uint8_t i8155_device::io_r(offs_t offset)
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data = m_status;
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// clear timer flag
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m_status &= ~STATUS_TIMER;
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if (!machine().side_effects_disabled())
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m_status &= ~STATUS_TIMER;
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break;
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case REGISTER_PORT_A:
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@ -432,11 +447,11 @@ uint8_t i8155_device::io_r(offs_t offset)
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break;
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case REGISTER_TIMER_LOW:
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data = m_counter & 0xff;
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data = get_timer_count() & 0xff;
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break;
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case REGISTER_TIMER_HIGH:
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data = (m_counter >> 8 & 0x3f) | get_timer_mode();
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data = (get_timer_count() >> 8 & 0x3f) | get_timer_mode();
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break;
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}
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@ -71,7 +71,6 @@ protected:
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// device-level overrides
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virtual void device_start() override;
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virtual void device_reset() override;
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virtual void device_timer(emu_timer &timer, device_timer_id id, int param, void *ptr) override;
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private:
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devcb_read8 m_in_pa_cb;
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@ -100,16 +99,17 @@ private:
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// counter
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uint16_t m_count_length; // count length register (assigned)
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uint16_t m_count_loaded; // count length register (loaded)
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uint16_t m_counter; // counter register
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bool m_count_extra; // extra cycle when count is odd
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int m_to; // timer output
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bool m_count_even_phase;
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// timers
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emu_timer *m_timer; // counter timer
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emu_timer *m_timer_tc; // counter timer (for TC)
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const address_space_config m_space_config;
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inline uint8_t get_timer_mode();
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inline uint8_t get_timer_mode() const;
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inline uint16_t get_timer_count() const;
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inline void timer_output(int to);
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inline void timer_stop_count();
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inline void timer_reload_count();
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@ -119,6 +119,9 @@ private:
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void write_command(uint8_t data);
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void register_w(int offset, uint8_t data);
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TIMER_CALLBACK_MEMBER(timer_half_counted);
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TIMER_CALLBACK_MEMBER(timer_tc);
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};
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