NDMA Registers

3DS NDMA has 8 channels. The first 0x100-bytes of this IO mem is mirrored at 0x10002100, repeated every 0x100-bytes until the end of the 0x1000-byte IO mem. NDMA can access the ARM9 bootrom, including the protected part before it is locked out.

Registers

Old3DS	Name	Address	Width	Used by
Yes	NDMA_GLOBAL_CNT	0x10002000	4	Boot9, Kernel9
Yes	NDMA_SRC_ADDR(n)	0x10002004 + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_DST_ADDR(n)	0x10002008 + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_TRANSFER_CNT(n)	0x1000200c + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_WRITE_CNT(n)	0x10002010 + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_BLOCK_CNT(n)	0x10002014 + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_FILL_DATA(n)	0x10002018 + (n*0x1c)	4	Boot9, Kernel9
Yes	NDMA_CNT(n)	0x1000201C + (n*0x1c)	4	Boot9, Kernel9

NDMA_GLOBAL_CNT

Bit	Description
0	Global enable?
19-16	Cycle selection.
31	DMA arbitration method. 0=Fixed method, 1=Round robin

NDMA_SRC_ADDR

Bit	Description
31-0	Source data address. Must be multiple of 4.

Like old DMA, NDMA_SRC_ADDR is copied to internal registers when written to.

NDMA_DST_ADDR

BIT	DESCRIPTION
31-0	Destination data address. Must be multiple of 4.

Like old DMA, NDMA_DST_ADDR is copied to internal registers when written to.

NDMA_TRANSFER_CNT

Bit	Description
27-0	Total number of words transferred.

NDMA_WRITE_CNT

Bit	Description
23-0	Number of words to transfer.

NDMA_BLOCK_CNT

Bit	Description
15-0	Interval timer.
17-16	Prescaler. 0=System freq, 1=1/4th freq, 2=1/16th freq, 3=1/64th freq.

NDMA_FILL_DATA

Bit	Description
31-0	Fill data.

NDMA_CNT

Bit	Description
11-10	Destination address update method. 0=Increment, 1=Decrement, 2=Fixed.
12	Destination address reload flag.
14-13	Source address update method. 0=Increment, 1=Decrement, 2=Fixed, 3=No address (for filling)
15	Source address reload flag.
19-16	Block transfer word count = (1<<x) words.
27-24	Startup mode.
28	Immediate mode.
29	Repeating mode.
30	IRQ enable
31	Enable/busy flag.

Startup modes (27-24)

Value	Description
0	TIMER0
1	TIMER1
2	TIMER2
3	TIMER3
4	CTRCARD0
5	CTRCARD1
6	MMC1
7	MMC2?
8	AES in (WRFIFO)
9	AES out (RDFIFO)
10	SHA in (INFIFO)
11	SHA out (INFIFO)
12	?
13	?
14	?
15	Boot9 Uses this to copy from the AES out FIFO to the SHA in FIFO

Block transfers

First, a word is always 32 bits. Second, the block transfer specified in NDMA_CNT is the smallest atom of data that will be transferred in a burst. The bus is monopolized until this block is transferred, without splitting up.

The next block transfer will happen after the specified time in the NDMA_BLOCK_CNT interval timer, until done.

Immediate mode

Transfers the words specified in NDMA_WRITE_CNT immediately following block transfer rules. NDMA_TRANSFER_CNT and repeating mode are ignored.

Repeating mode

Transfers the words specified in NDMA_WRITE_CNT following the startup mode event. NDMA_TRANSFER_CNT is ignored.

No immediate and no repeating mode

Transfers the words specified in NDMA_WRITE_CNT for each startup event, and gets disabled when the total number of words in NDMA_TRANSFER_CNT are transferred.