SPI Registers

Registers

Old3DS	Name	Address	Width	Used by
Yes	SPI_CNT1	0x10142000	2
Yes	SPI_DATA1	0x10142002	1
Yes	NSPI_CNT1	0x10142800	4
Yes	NSPI_DONE1	0x10142804	4
Yes	NSPI_BLKLEN1	0x10142808	4
Yes	NSPI_FIFO1	0x1014280C	4
Yes	NSPI_STATUS1	0x10142810	4
Yes	NSPI_AUTOPOLL1	0x10142814	4	-
Yes	NSPI_INT_MASK1	0x10142818	4	-
Yes	NSPI_INT_STAT1	0x1014281C	4	-
Yes	SPI_CNT2	0x10143000	2
Yes	SPI_DATA2	0x10143002	1
Yes	NSPI_CNT2	0x10143800	4
Yes	NSPI_DONE2	0x10143804	4
Yes	NSPI_BLKLEN2	0x10143808	4
Yes	NSPI_FIFO2	0x1014380C	4
Yes	NSPI_STATUS2	0x10143810	4
Yes	NSPI_AUTOPOLL2	0x10143814	4	-
Yes	NSPI_INT_MASK2	0x10143818	4	-
Yes	NSPI_INT_STAT2	0x1014381C	4	-
Yes	SPI_CNT3	0x10160000	2
Yes	SPI_DATA3	0x10160002	1
Yes	NSPI_CNT3	0x10160800	4
Yes	NSPI_DONE3	0x10160804	4
Yes	NSPI_BLKLEN3	0x10160808	4
Yes	NSPI_FIFO3	0x1016080C	4
Yes	NSPI_STATUS3	0x10160810	4
Yes	NSPI_AUTOPOLL3	0x10160814	4	-
Yes	NSPI_INT_MASK3	0x10160818	4	-
Yes	NSPI_INT_STAT3	0x1016081C	4	-

There are two register interfaces: the old NDS/DSi one and an alternative faster interface introduced with the 3DS.

To toggle between those interfaces, use the CFG11_SPI_CNT register.

SPI_CNT

This is the old NDS/DSi SPI interface.

Bits	Name
0-1	Baudrate (0=4MHz, 1=2MHz, 2=1MHz, 3=512KHz)
2-6	This was added with 3DS.
7	Busy Flag (0=Ready, 1=Busy) (presumably Read-only)
8-9	Device Select (0=Powerman., 1=Firmware, 2=Touchscreen)
10	Transfer Size (0=8bit/Normal, 1=16bit/Bugged)
11	Chipselect Hold (0=Deselect after transfer, 1=Keep selected)
12-13	Not used (Zero)
14	Interrupt Request (0=Disable, 1=Enable)
15	SPI Bus Enable (0=Disable, 1=Enable)

NSPI_CNT

This is an alternative faster interface introduced with the 3DS.

Bits	Name
0-2	Clock
6-7	Device select
12	Bus mode (0 = 1 bit, 1 = 4 bit)
13	Transfer direction (0 = read, 1 = write)
15	1 = Busy/enable

Device id	Bus	Device select	Clock
0	3	0	2
1, 2	3	1, 2	?, ?
3	1	0	5
4, 5	1	1, 2	?, ?
6	2	0	?

NSPI_DONE

BIT	DESCRIPTION
0	Chip select
1-31	Unused

Contains 1 when the SPI slave is selected. A 0 is written here on transfer end to deselect the slave.

NSPI_BLKLEN

BIT	DESCRIPTION
0-20	Transfer size
21-31	Unused

The number of bytes to be sent/read is written to this register.

NSPI_FIFO

BIT	DESCRIPTION
0-31	Data

32-bit FIFO for reading/writing the SPI payload. This FIFO is one way (half-duplex).

NSPI_STATUS

BIT	DESCRIPTION
0	FIFO full (0 = not full, 1 = full)
1-31	Unused

At transfer start and every 32 bytes the FIFO becomes busy.

NSPI_AUTOPOLL

BIT	DESCRIPTION
0-7	Command
16-19	Timeout (Tries = 31<<Clock (from NSPI_CNT) + Timeout)
24-26	Bit offset (0-7)
30	Poll for a set or unset bit
31	1 = Enable/Busy

This automatically sends a command to the device and compares the specified bit in the response with bit 30 until it matches or a timeout occurs.

NSPI_INT_MASK

BIT	DESCRIPTION
0	Transfer finished (1 = disabled)
1	Autopoll success (1 = disabled)
2	Autopoll timeout (1 = disabled)

NSPI_INT_STAT

BIT	DESCRIPTION
0	Transfer finished (also fires on each autopoll try?)
1	Autopoll success
2	Autopoll timeout

Interrupt ID 0x24, 0x56 or 0x57 (depending on the bus) is fired when any of the bits change to 1 except for interrupts masked in NSPI_INT_MASK. Writing 1 to a bit in this register aknowledges the interrupt.