SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Each descriptor line contains an address, a length, and attributes fields. The attributes define which operation will be processed. Every descriptor line is a 64-bit-wide register that is fetched in the controller using the L3_MAIN master interface, and requires two 32-bit accesses to memory.
Table 25-12 shows the structure of a descriptor line.
Address Field | Length | Reserved | Attributes | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
63 | 32 | 31 | 16 | 15 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
32-bit address | 16-bit length | 0x0 | Act2 | Act1 | 0 | Int | Ent | Valid |
The attribute of the descriptor line is divided into two parts:
Table 25-13 describes the available actions of a descriptor line.
Act2 | Act1 | Symbol | Comment | Operation |
---|---|---|---|---|
0 | 0 | Nop | No operation | Do not execute the current line and go to the next line. |
0 | 1 | Rsv | Reserved | Reserved action. Behaves the same as the Nop command. |
1 | 0 | Tran | Transfer data | Transfer data of one descriptor line. |
1 | 1 | Link | Link descriptor | Link to another descriptor. |
Table 25-14 describes the additional parameters of a descriptor line.
Bit | Description |
---|---|
Valid | Valid = 1 indicates that this descriptor line is effective. If Valid = 0, an ADMA error interrupt is generated and the ADMA is stopped. This prevents runaways. |
End | End = 1 indicates the end of a descriptor. The transfer-complete interrupt is generated when the operation of the descriptor line is complete. |
Int | Int = 1 generates a DMA interrupt when the operation of the descriptor line is complete. |