Scatter Gather DMA in Xilinx FPGA

Comments

Introduction

Naming convetion and System diagram

Register in Xilinx DMA IP

Scatter Gather Descriptor

  1. The descriptor is made up of eight 32-bit base words and 0 or 5 User Application words.
  2. The Buffer Length can describe up to 67,108,863 bytes of data buffer per descriptor.
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Descriptor Fields (Non-multichannel Mode)
Address Space Offset (1) Name Description
00h     NXTDESC               Next Descriptor Pointer
04h     NXTDESC_MSB           Upper 32 bits of Next Descriptor Pointer
08h     BUFFER_ADDRESS        Buffer Address
0Ch     BUFFER_ADDRESS_MSB    Upper 32 bits of Buffer Address.
10h     RESERVED              N/A
14h     RESERVED              N/A
18h     CONTROL               Control
1Ch     STATUS                Status
20h     APP0                  User Application Field 0 (2)
24h     APP1                  User Application Field 1
28h     APP2                  User Application Field 2
2Ch     APP3                  User Application Field 3
30h     APP4                  User Application Field 4

Data Structure for Scatter Gather Descriptor

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struct sg_bd{
    unsigned int nxtdesc;// 
    unsigned int nxtdesc_msb;
    unsigned int buf_addr; // address of the data to trasnfer from memory map to stream, 
                          // should be aligned to the memory map data width
    unsigned int buf_addr_msb;//
    unsigned int reserved0;
    unsigned int reserved1;
    unsigned int ctrl; // 0x1c
    unsigned int status;
    unsigned int app0 ;
    unsigned int app1 ;
    unsigned int app2;
    unsigned int app3;
    unsigned int app4;
    unsigned int dummy[3];
};

MM2S_CONTROL register (0x18h)

The value of thie register provides control for MM2S transfers from memory map to stream.

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Bits        Field Name                            Description
25 to 0    Buffer Length          Indicates the size in bytes of the transfer buffer.
26   	Transmit End Of Frame     End of Frame. Flag indicating the last buffer to be processed. 
                                  • 0 = Not End of Frame. 
                                  • 1 = End of Frame.
27            TXSOF               Start of Frame. Flag indicating the first buffer to be processed.