I2C Bus

Registers

NAME	ADDRESS	WIDTH
REG_I2CDATA	0x04004500	1
REG_I2CCNT	0x04004501	1

REG_I2CCNT

BIT	DESCRIPTION
0	R/W, clear for write, set for read
1	Start/device select bit?
2	Restart/device reselect bit?
3	?
4	SCL hold. When clear SCL is being held low, set when SCL is high. This bit must always be set(by reading CNT again) after writing REG_I2CCNT. This bit must be set when writing blocks of data(more than 1 byte) with bit0 clear.
5	SCL, toggle this for each loop iteration(in the loop execute the I2C WR code) with max 8 iterations where the loop exits successfully when bit 4 is set. This bit must be set when writing blocks of data(more than 1 byte) with bit0 clear.
6	Unknown, always set when writing to CNT?
7	Enable/busy, wait for this bit to clear after writing to I2CCNT.

REG_I2CDATA

When selecting a register, the register byte address is written here. When reading or writing data to the I2C device, it's read/written from here. When selecting a device, the device byte address is written here. Bit0 is unknown, when reading from certain devices, the device is first selected and then the register, following that the device is reselected with device byte address bit0 set.

Protocol

Wait for the busy bit to clear. Write the device address to REG_I2CDATA, then write 0xc2(busy/enable, bit 6, and start bit 1 set) to REG_I2CCNT. Execute swiWaitByLoop for a device-specific duration, then write the register address to REG_I2CDATA, and write 0xc0 to REG_I2CCNT.(busy/enable and bit 6 set) Wait with swiWaitByLoop device duration, then write the data to REG_I2CDATA when writing. When reading, write the device address to REG_I2CDATA and write 0xc2 to REG_I2CCNT. When the delay value is zero, write 0xc1 | i<<5 to REG_I2CCNT, otherwise write 0xc0 | i<<5 to REG_I2CCNT, wait for busy to clear, delay, then write 0xc5 to REG_I2CCNT. For writing i is the loop i for iteration, for reading replace that with 1. When reading, read the data from REG_I2CCNT. Return a error if REG_I2CCNT bit 4 SCL hold is set, otherwise return normal.

I2C devices

I2C device table:

Device address	Device swiWaitByLoop delay	I2CDATA bit0 set with dev addr required for reading	Device description
0x7A	0x00	No	Camera0?
0x78	0x00	No	Camera1?
0xA0	0x00	No	?
0xE0	0x00	No	?
0x4A	0x180	Yes	Power management
0x40	0x00	Yes	?
0x90	0x00	Yes	?

Power management

When register 0x11 has value one written to, a power cycle is done. When reg 0x70 val 1 is written before reg 0x11, sysmenu/launcher doesn't display the heath screen, otherwise when not written the health screen is displayed.

REGISTER	WIDTH	DESCRIPTION
0x0	1	Unknown, battery related? Usually this reg val is 0x33?
0x10	1	Power flags. When bit0 is set, arm7 does a system reset. When bit1 or bit3 are set, arm7 does a shutdown.
0x11	1	Power reg? Writing value 1 here does a system reset. Writing value 2 powers off all DSi-only hw.
0x12	1	Might be MMC bus power related, unknown.
0x20	1	Battery flags. When zero the battery is at critical level, arm7 does a shutdown. Bit7 is set when the battery is charging. When the battery icon is full bars, this is 0x0F, and when the battery icon has one solid red bar left this is 0x03?
0x21	1	?
0x31	1	External camera LED control, valid values are 0-2. Value 0 disables the LED, value 1 activates the LED, value 2 activates the LED with the LED blinking.
0x40	1	?
0x70	1	Power related?