Registers

Old3DS	Name	Address	Width
Yes	PXI_SYNC9	0x10008000	4
Yes	PXI_CNT9	0x10008004	4
Yes	PXI_SEND9	0x10008008	4
Yes	PXI_RECV9	0x1000800C	4
Yes	PXI_SYNC11	0x10163000	4
Yes	PXI_CNT11	0x10163004	4
Yes	PXI_SEND11	0x10163008	4
Yes	PXI_RECV11	0x1016300C	4

The PXI registers are similar to those on DS.

PXI_SYNC

Bit	RW	Description
0-7	R	Data received from remote bits 8-15 (unrelated to SEND/RECV FIFOs)
8-15	R/W	Data sent to remote bits 0-7
23	?	?
29	W?	Trigger PXI_SYNC11 IRQ (if enabled)
30	W?	Trigger PXI_SYNC9 IRQ (if enabled)
31	RW	PXI_SYNC IRQ enable (for local processor)

This can also be accessed as 4 u8 registers.

Bit	RW	Description
0	R	Send Fifo Empty Status (0=Not Empty, 1=Empty)
1	R	Send Fifo Full Status (0=Not Full, 1=Full)
2	R/W	Send Fifo Empty IRQ (0=Disable, 1=Enable)
3	W	Send Fifo Clear (0=Nothing, 1=Flush Send Fifo)
8	R	Receive Fifo Empty (0=Not Empty, 1=Empty)
9	R	Receive Fifo Full (0=Not Full, 1=Full)
10	R/W	Receive Fifo Not Empty IRQ (0=Disable, 1=Enable)
14	R/W	Error, Read Empty/Send Full (0=No Error, 1=Error/Acknowledge)
15	R/W	Enable Send/Receive Fifo (0=Disable, 1=Enable)