Intel® Agilex™ Hard Processor System Technical Reference Manual

ID 683567
Date 11/11/2022
Public

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Document Table of Contents

16.4.2.5.8. Internal DMA Controller Functional State Machine†

The following list explains each state of the functional state machine:

  1. The internal DMA controller performs four accesses to fetch a descriptor.
  2. The DMA controller stores the descriptor information internally. If it is the first descriptor, the controller issues a FIFO buffer reset and waits until the reset is complete.
  3. The internal DMA controller checks each bit of the descriptor for the correctness. If bit mismatches are found, the appropriate error bit is set to 1 and the descriptor is closed by setting the OWN bit in the DES0 field to 1.

    The rintsts register indicates one of the following conditions:

    • Response timeout
    • Response CRC error
    • Data receive timeout
    • Response error
  4. The DMA waits for the RX watermark to be reached before writing data to system memory, or the TX watermark to be reached before reading data from system memory. The RX watermark represents the number of bytes to be locally stored in the FIFO buffer before the DMA writes to memory. The TX watermark represents the number of free bytes in the local FIFO buffer before the DMA reads data from memory.
  5. If the value of the programmable burst length (PBL) field is larger than the remaining amount of data in the buffer, single transfers are initiated. If dual buffers are being used, and the second buffer contains no data (buffer size = 0), the buffer is skipped and the descriptor is closed.
  6. The OWN bit in descriptor is set to 0 by the internal DMA controller after the data transfer for one descriptor is completed. If the transfer spans more than one descriptor, the DMA controller fetches the next descriptor. If the transfer ends with the current descriptor, the internal DMA controller goes to idle state after setting the ri bit or the ti bit of the idsts register. Depending on the descriptor structure (dual buffer or chained), the appropriate starting address of descriptor is loaded. If it is the second data buffer of dual buffer descriptor, the descriptor is not fetched again.