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'''boot2''' is the [[Wii]]'s third-stage bootloader. It is responsible for loading the [[System Menu]] [[TMD]] and loading the appropriate [[IOS]] under normal circumstances, although it can also load [[MIOS]] if it detects the lowered clock speed set by [[BC]] (if [[IOS/Syscalls|syscall 55]] returns 162).

'''boot2''' is the [[Wii]]'s third-stage bootloader. It is responsible for loading the [[System Menu]] [[TMD]] and loading the appropriate [[IOS]] under normal circumstances, although it can also load [[MIOS]] if it detects the lowered clock speed set by [[BC]] (if [[IOS/Syscalls|syscall 55]] returns 162).

Like IOS, boot2 has multiple modules. In this way, it can be thought of as an IOS installed to a special part of the NAND. However, all modules are contained within a single binary, much like IOSes before [[IOS28]]. Boot2 has a kernel with IOSC functionality, an ES module, and an FS module. Unlike IOS, get_kernel_flavor writes 0 to the first argument instead of 3, which distinguishes it from IOS.

Like IOS, boot2 has multiple modules. In this way, it can be thought of as an IOS installed to a special part of the [[NAND]]. However, all modules are contained within a single binary, much like IOSes before [[IOS28]]. Boot2 has a kernel with IOSC functionality, an ES module, and an FS module. Unlike IOS, get_kernel_flavor writes 0 to the first argument instead of 3, which distinguishes it from IOS.

boot2 is also launched by MIOS when the power button is pressed; the System Menu is initialized in this case, and [[Memory Map|0x80003164]] <!-- read as c0003164 by the system menu; written as 00003164 by boot2 --> is set to 1 if the SRSTB_CPU bit is set in [[Hardware/Hollywood_Registers#HW_RESETS|HW_RESETS]]; the System Menu checks 0x80003164 and shuts down if it is enabled and [[:/title/00000001/00000002/data/state.dat|state.dat]] is set appropriately, with the message "Shutdown system from GC!".

boot2 is also launched by MIOS when the power button is pressed; the System Menu is initialized in this case, and [[Memory Map|0x80003164]] <!-- read as c0003164 by the system menu; written as 00003164 by boot2 --> is set to 1 if the SRSTB_CPU bit is set in [[Hardware/Hollywood_Registers#HW_RESETS|HW_RESETS]]; the System Menu checks 0x80003164 and shuts down if it is enabled and [[:/title/00000001/00000002/data/state.dat|state.dat]] is set appropriately, with the message "Shutdown system from GC!".

There are two copies of boot2 housed in [[Hardware/NAND|NAND]] blocks 1-7 in case of failure, loaded by [[boot1]].

There are two copies of boot2 housed in [[Hardware/NAND|NAND]] blocks 1-7 in case of failure, loaded by [[boot1]]. boot2 seems to include code to complete the update if it detects [[:/sys/boot.sys]] on the NAND; this code is probably prone to bugs.

boot2 was updated in the [[4.2]] update to [[boot2v4]], the only time Nintendo has ever pushed a boot2 update, besides on [[Prelaunch System Menu|prelaunch consoles]]. This was done by calling ES_ImportBoot to install it into the boot2 region of the NAND. Unfortunately, Nintendo did not test ES_ImportBoot very well, which led to many Wiis receiving a [[Brick#Low Level Brick (LLB)|low-level brick]], even if they were previously unmodded. The cause of this is unknown, although it may be related to the failure to write ECC data.

boot2 was updated in the [[4.2]] update to [[boot2v4]], the only time Nintendo has ever pushed a boot2 update, besides on [[Prelaunch System Menu|prelaunch consoles]]. This was done by calling ES_ImportBoot to install it into the boot2 region of the NAND. Unfortunately, Nintendo did not test ES_ImportBoot very well, which led to many Wiis receiving a [[Brick#Low Level Brick (LLB)|low-level brick]], even if they were previously unmodded. The cause of this is unknown, although it may be related to the failure to write ECC data.