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.
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?
|
| 1
|
Autopoll success
|
| 2
|
Autopoll timeout
|
Interrupt ID 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.