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 (unprotected) part of the bootrom.
Registers
| Old3DS | Name | Address | Width | Used by |
|---|---|---|---|---|
| Yes | NDMA_GLOBAL_CNT | 0x10002000 | 4 | |
| Yes | NDMA_SRC_ADDR(n) | 0x10002004 + (n*0x1c) | 4 | |
| Yes | NDMA_DST_ADDR(n) | 0x10002008 + (n*0x1c) | 4 | |
| Yes | NDMA_TRANSFER_CNT(n) | 0x1000200c + (n*0x1c) | 4 | |
| Yes | NDMA_WRITE_CNT(n) | 0x10002010 + (n*0x1c) | 4 | |
| Yes | NDMA_BLOCK_CNT(n) | 0x10002014 + (n*0x1c) | 4 | |
| Yes | NDMA_FILL_DATA(n) | 0x10002018 + (n*0x1c) | 4 | |
| Yes | NDMA_CNT(n) | 0x1000201C + (n*0x1c) | 4 |
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)
???
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.