Reducing Power Consumption - Revision history

Nitro2k01 at 02:42, 5 April 2020

2020-04-05T02:42:55Z

ISSOtm: /* Using the Skills */ Added a link to a wiki page helping finding optimizations, although designed for the Z80 and not for the GBZ80. May still be useful, though.

2015-12-15T22:39:52Z

‎Using the Skills: Added a link to a wiki page helping finding optimizations, although designed for the Z80 and not for the GBZ80. May still be useful, though.

ISSOtm: /* Using the STOP Instruction */ Added a precision about the impact of the STOP instruction on user experience.

2015-12-15T22:36:39Z

‎Using the STOP Instruction: Added a precision about the impact of the STOP instruction on user experience.

ISSOtm: /* Using the HALT Instruction */ Added a way of waiting a single frame, which I use in my game. Tested it, it works fine. Also added a note to remember that the interrupt routines MUST enable interrupts during / after execution.

2015-12-15T20:22:48Z

‎Using the HALT Instruction: Added a way of waiting a single frame, which I use in my game. Tested it, it works fine. Also added a note to remember that the interrupt routines MUST enable interrupts during / after execution.

Tpw rules: Fixing spelling, doing some rephrasing

2011-03-16T16:59:23Z

Fixing spelling, doing some rephrasing

Xzakox at 13:03, 28 June 2009

2009-06-28T13:03:25Z

Xzakox: New page: The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries. == PWR Using the HALT Instruction == It is recommended that the HALT in...

2009-06-28T11:08:52Z

New page: The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries. == PWR Using the HALT Instruction == It is recommended that the HALT in...

New page

The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries.

== PWR Using the HALT Instruction ==

It is recommended that the HALT instruction be used whenever possible to reduce power consumption & extend the life of the batteries. This command stops the system clock reducing the power consumption of both the CPU and ROM.

The CPU will remain suspended until an interrupt occurs at which point the interrupt is serviced and then the instruction immediately following the HALT is executed.

Depending on how much CPU time is required by a game, the HALT instruction can extend battery life anywhere from 5 to 50% or possibly more.

When waiting for a vblank event, this would be a BAD example:

@@wait:
ld a,(0FF44h) ;LY
cp a,144
jr nz,@@wait

A better example would be a procedure as shown below. In this case the vblank interrupt must be enabled, and your vblank interrupt procedure must set vblank_flag to a non-zero value.

ld hl,vblank_flag ;hl=pointer to vblank_flag
xor a ;a=0
@@wait: ;wait...
halt ;suspend CPU - wait for ANY interrupt
cp a,(hl) ;vblank flag still zero?
jr z,@@wait ;wait more if zero
ld (hl),a ;set vblank_flag back to zero

The vblank_flag is used to determine whether the HALT period has been terminated by a vblank interrupt, or by another interrupt. In case that your program has all other interrupts disabled, then it would be proof to replace the above procedure by a single HALT instruction.

== PWR Using the STOP Instruction ==

The STOP instruction is intended to switch the gameboy into VERY low power standby mode. For example, a program may use this feature when it hasn't sensed keyboard input for a longer period (assuming that somebody forgot to turn off the gameboy).

Before invoking STOP, it might be required to disable Sound and Video manually (as well as IR-link port in CGB). Much like HALT, the STOP state is terminated by interrupt events - in this case this would be commonly a joypad interrupt. The joypad register might be required to be prepared for STOP either.

== PWR Disabeling the Sound Controller ==

If your programs doesn't use sound at all (or during some periods) then write 00h to register FF26 to save 16% or more on GB power consumption.
Sound can be turned back on by writing 80h to the same register, all sound registers must be then re-initialized.
When the gameboy becomes turned on, sound is enabled by default, and must be turned off manually when not used.

== PWR Not using CGB Double Speed Mode ==

Because CGB Double Speed mode consumes more power, it'd be recommended to use normal speed when possible.
There's limited ability to switch between both speeds, for example, a game might use normal speed in the title screen, and double speed in the game, or vice versa.
However, during speed switch the display collapses for a short moment, so that it'd be no good idea to alter speeds within active game or title screen periods.

== PWR Using the Skills ==

Most of the above power saving methods will produce best results when using efficient and tight assembler code which requires as less CPU power as possible. Thus, experienced old-school programmers will (hopefully) produce lower power consumption, as than HLL-programming teenagers, for example.

← Older revision		Revision as of 02:42, 5 April 2020
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−	{{Pandocs\|~~reducingpowerconsumption~~}}	+	{{Pandocs\|reducing-power-consumption}}
	The following programming techniques can be used to reduce the power consumption of the GameBoy hardware and extend the life of the batteries.		The following programming techniques can be used to reduce the power consumption of the GameBoy hardware and extend the life of the batteries.

← Older revision		Revision as of 22:39, 15 December 2015
Line 62:		Line 62:

	Most of the above power saving methods will produce best results when using efficient and tight assembler code which requires as little CPU power as possible. Using a high level language will require more CPU power and these techniques will not have as big as an effect.		Most of the above power saving methods will produce best results when using efficient and tight assembler code which requires as little CPU power as possible. Using a high level language will require more CPU power and these techniques will not have as big as an effect.
		+
		+	To optimize you code, it might be a good idea to look at [http://wikiti.brandonw.net/index.php?title=Z80_Optimization this page], although it applies to the original Z80 CPU, so one must adapt the optimizations to the GBZ80.

← Older revision		Revision as of 22:36, 15 December 2015
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	Before invoking STOP, it might be required to disable Sound and Video manually (as well as IR-link port in CGB). Much like HALT, the STOP state is terminated by interrupt events. STOP is commonly terminated with a joypad interrupt.		Before invoking STOP, it might be required to disable Sound and Video manually (as well as IR-link port in CGB). Much like HALT, the STOP state is terminated by interrupt events. STOP is commonly terminated with a joypad interrupt.

		+	During STOP mode, the display will turn white, so avoid using it in your game's main loop.

	== Disabling the Sound Controller ==		== Disabling the Sound Controller ==

← Older revision		Revision as of 20:22, 15 December 2015
Line 30:		Line 30:
	The vblank_flag is used to determine whether the HALT period has been terminated by a vblank interrupt, or by another interrupt. In case your program has all other interrupts disabled, then it would be okay to replace the above procedure by a single HALT instruction.		The vblank_flag is used to determine whether the HALT period has been terminated by a vblank interrupt, or by another interrupt. In case your program has all other interrupts disabled, then it would be okay to replace the above procedure by a single HALT instruction.

		+
		+	Another possibility is, if your game uses no other interrupt than VBlank (or uses no interrupt), to only enable VBlank interrupts and simply use a halt instruction, which will only resume main code execution when a VBlank occurs.
		+
		+
		+
		+	Remember when using HALT to wait between VBlanks, your interrupt routines MUST enable interrupts (ie with ei during the execution, or better, using the RETI instruction)

	== Using the STOP Instruction ==		== Using the STOP Instruction ==

← Older revision		Revision as of 13:03, 28 June 2009
Line 1:		Line 1:
		+	{{Pandocs\|reducingpowerconsumption}}
	The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries.		The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries.

@@ Line 1: / Line 1: @@
 {{Pandocs|reducingpowerconsumption}}
-The following can be used to recude the power consumption of the gameboy, and to extend the life of the batteries.
+The following programming techniques can be used to reduce the power consumption of the GameBoy hardware and extend the life of the batteries.
-== PWR Using the HALT Instruction ==
+== Using the HALT Instruction ==
-It is recommended that the HALT instruction be used whenever possible to reduce power consumption & extend the life of the batteries. This command stops the system clock reducing the power consumption of both the CPU and ROM.
+The HALT instruction should be used whenever possible to reduce power consumption & extend the life of the batteries. This command stops the system clock, reducing the power consumption of both the CPU and ROM.
-The CPU will remain suspended until an interrupt occurs at which point the interrupt is serviced and then the instruction immediately following the HALT is executed.
+The CPU will remain stopped until an interrupt occurs at which point the interrupt is serviced and then the instruction immediately following the HALT is executed.
 Depending on how much CPU time is required by a game, the HALT instruction can extend battery life anywhere from 5 to 50% or possibly more.
@@ Line 28: / Line 28: @@
     ld   (hl),a          ;set vblank_flag back to zero
-The vblank_flag is used to determine whether the HALT period has been terminated by a vblank interrupt, or by another interrupt. In case that your program has all other interrupts disabled, then it would be proof to replace the above procedure by a single HALT instruction.
+The vblank_flag is used to determine whether the HALT period has been terminated by a vblank interrupt, or by another interrupt. In case your program has all other interrupts disabled, then it would be okay to replace the above procedure by a single HALT instruction.
-== PWR Using the STOP Instruction ==
+== Using the STOP Instruction ==
-The STOP instruction is intended to switch the gameboy into VERY low power standby mode. For example, a program may use this feature when it hasn't sensed keyboard input for a longer period (assuming that somebody forgot to turn off the gameboy).
+The STOP instruction is intended to switch the gameboy into VERY low power standby mode. For example, a program may use this feature when it hasn't sensed keyboard input for a longer period (for example, when somebody forgot to turn off the gameboy).
-Before invoking STOP, it might be required to disable Sound and Video manually (as well as IR-link port in CGB). Much like HALT, the STOP state is terminated by interrupt events - in this case this would be commonly a joypad interrupt. The joypad register might be required to be prepared for STOP either.
+Before invoking STOP, it might be required to disable Sound and Video manually (as well as IR-link port in CGB). Much like HALT, the STOP state is terminated by interrupt events. STOP is commonly terminated with a joypad interrupt.
-== PWR Disabeling the Sound Controller ==
+== Disabling the Sound Controller ==
-If your programs doesn't use sound at all (or during some periods) then write 00h to register FF26 to save 16% or more on GB power consumption.
+If your program doesn't use sound at all (or during some periods) then write 00h to register FF26 to save 16% or more on GB power consumption.
 Sound can be turned back on by writing 80h to the same register, all sound registers must be then re-initialized.
-When the gameboy becomes turned on, sound is enabled by default, and must be turned off manually when not used.
+When the gameboy is turned on, sound is enabled by default, and must be turned off manually when not used.
-== PWR Not using CGB Double Speed Mode ==
+== Not using CGB Double Speed Mode ==
-Because CGB Double Speed mode consumes more power, it'd be recommended to use normal speed when possible.
+Because CGB Double Speed mode consumes more power, it's recommended to use normal speed when possible.
 There's limited ability to switch between both speeds, for example, a game might use normal speed in the title screen, and double speed in the game, or vice versa.
-However, during speed switch the display collapses for a short moment, so that it'd be no good idea to alter speeds within active game or title screen periods.
+However, during speed switch, the display collapses for a short moment, so it's not a good idea to alter speeds within active game or title screen periods.
-== PWR Using the Skills ==
+== Using the Skills ==
-Most of the above power saving methods will produce best results when using efficient and tight assembler code which requires as less CPU power as possible. Thus, experienced old-school programmers will (hopefully) produce lower power consumption, as than HLL-programming teenagers, for example.
+Most of the above power saving methods will produce best results when using efficient and tight assembler code which requires as little CPU power as possible. Using a high level language will require more CPU power and these techniques will not have as big as an effect.