Hardware/RTC

General

Just like the Wii and the GameCube, the Wii U contains a dedicated chip for the Real-Time Clock (RTC). The MX23L0002 is a custom chip that encompasses the RTC and a small SRAM bank. While the chip still sits on the EXI bus (channel 0, device 1) it no longer contains the GameCube font sets, as this data is now handled on the software side.

Communication

To access the RTC on the Wii U you must:

- Enable the EXI through HW_AIP_PROT;
- Initialize the EXI channels;
- Register device 1 (RTC) on EXI channel 0 with default frequency;
- To read from the RTC:
    -> EXI immediate write the RTC offset (see below);
    -> EXI immediate read the result;
- To write to the RTC:
    -> EXI immediate write the RTC offset (see below) ORed with flag 0x80000000;
    -> EXI immediate write the desired value;
- Reset the EXI channel.

RTC offsets

The RTC exposes a few control registers and SRAM memory access in the form of EXI offsets, which can be accessed to read and write 32-bit values or perform DMA operations (in the case of SRAM).

Name	Offset	Description
RTC_COUNTER	0x20000000	Contains the counting time intervals in seconds
RTC_SRAM	0x20000100	Battery backed memory The SRAM has a total size of 64 bytes, starting at offset 0x20000100 and ending at offset 0x20001000. Therefore, each word is located at (0x20000100 + 0x100 * i) with (i < 0x10). On Wii U mode (recent firmware versions only), this memory is used to store IOSU kernel panic strings.
RTC_SNAPSHOT	0x20400000	Contains a snapshot of RTC_COUNTER
ONTMR_SET	0x21000000	Contains the value set for the ON timer The value set here is masked with 0x3FFFFFFF and represents time intervals in seconds. The following flags can be set on the value's upper bits: 0x80000000 (ONTMR_EN): Enable/disable the ON timer. 0x40000000 (PONTMR_DTCT): Unknown.
OFFTMR_SET	0x21000100	Contains the value set for the OFF timer The value set here is masked with 0x3FFFFFFF and represents time intervals in seconds. The following flags can be set on the value's upper bits: 0x80000000 (OFFTMR_EN): Enable/disable the OFF timer. 0x40000000 (POFFTMR_DTCT): Unknown.
RTC_TEST0	0x21000400	Always 0x03030303 after power on (test pattern)
RTC_TEST1	0x21000500	Always 0x03030303 after power on (test pattern)
RTC_TEST2	0x21000600	Always 0x03030303 after power on (test pattern)
RTC_TEST3	0x21000700	Always 0x03030303 after power on (test pattern)
RTC_CONTROL0	0x21000C00	RTC control register 0 The last byte stored here (mask == 0x000000FF) is always RTC_REVISION (0x00 or 0x01). The following flags can be set here: 0x04000000 (POFFLG_FPOFF): Set upon a forced power off. 0x02000000 (POFFLG_4S): Set upon a 4 second power button press. 0x01000000 (POFFLG_TMR): Set upon a OFF timer power off. 0x00020000 (PONFLG_SYS): Set upon a system power event. 0x00010000 (PONLG_TMR): Set upon a ON timer power on. 0x00000800 (UNSTBL_PWR): Unknown. boot0 checks this before launching a recovery boot1 image. 0x00000200 (LOW_BATT): Set when the CMOS battery is worn off. 0x00000100 (CANARY): Used by IOS-ACP when handling the rtcflag0.dat and rtcflag1.dat files.
RTC_CONTROL1	0x21000D00	RTC control register 1 The following flags can be set here: 0x00010000 (POFF_EXE): Setting this flag executes a power off event. 0x00000400 (DEVPWR_EN or DEVPWR_SYNC): If set, this flag is referred to as DEVPWR_EN (device power enabled?). If not set, this flag is referred to as DEVPWR_SYNC (device power sync?). 0x00000100 (SLEEP_EN): Setting this flag puts the RTC in sleep mode (used in standby mode). 0x00000008 (FPOFF_MODE): This flag defines the forced power off event mode. 0x00000004 (CLKOUT_EN): This flag enables/disables the CLKOUT pin. 0x00000001 (4COUNT_EN): This flag enables/disables the 4 second power button press functionality.

Pinout

Counter-clockwise from the top-left dot:

Pin number (Bottom, 5x7)	Pin number (Top, 6x6)	Name	Description
01	01	crystal 1
02	02	GND
03	03	Reset?	TP144. Acts like a reset when pulled down using a 3.3kohm resistor. R677 can be severed to disconnect the signal from the SMC+RTC to the SoC.
04	04	VCC?	Goes to 3.3V plane on the PCB
05	05	?	TP146, trace goes near Bluetooth connector
06	06	?	TP143, directly to SoC
07	09	?	TP175, to SMC, clock? 1Hz 3.3V-0V
08	07	EXI MISO	Device out, Wii U in. TP176, directly to SoC
09	10	EXI MOSI	Device in, Wii U out
10	11	EXI CS	TP102, directly to SoC
11	12	?	directly to SoC? Has an in-line resistor
12	08	GND
13	13	EXI CLK	TP101
14	17	NC
15	14	2.4GHz power enable	TP141, enables Q1065 to send 3.3V standby to Wifi module
16	15	1.5V enable	TP149
17	16	15V PFET enable	TP147, enables Q1061 to send 15V to motherboard
18	18	?	TP9, Power Button (active low/pullup, pressed=0.0v, not pressed=3.3v), also connected to SMC
19	19	PGOOD?	TP148, pulled high by 3.3V standby
20	20	VCC?	3.3V Standby
21	21	SMC nRESET	TP145, to SMC
22	22	?	via to nowhere? capacitor to ground?
23	23	VCC backup batt
24	24	crystal 2