The gamepad has a pretty simple memory map.

It is not yet known how to access the bootloader or if it exists at FFFF0000. That region reads as zero.

The I/O region only properly supports 32-bit writes. 16-bit and 8-bit writes will cause the incoming data to be repeated across the entire 32-bit register, ie. a 16-bit write of 0x1234 will result in 0x12341234 being written to the entire 32-bit register.

The SDIO region has specific access requirements for each register, and trying to write to a register with the wrong size is simply ignored. TODO: document exactly which registers require which sizes.

The DRH SoC (on WiiU side) has a USB device controller at 0xE0000000. Not sure if this exists at all on the gamepad.

The I/O region is split into basic blocks for the various hardware components.