Intel® Agilex™ Hard Processor System Technical Reference Manual

ID 683567
Date 2/14/2023
Public

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16.5.7.2. Internal DMA Controller Transmission Sequences

To use the internal DMA controller to transmit data, perform the following steps:
  1. The host sets up the Descriptor fields (DES0—DES3) for transmission and sets the OWN bit (DES0[31]) to 1. The host also loads the data buffer in system memory with the data to be written to the SD card.
  2. The host writes the appropriate write data command (SD/SDIO WRITE_BLOCK or WRITE_MULTIPLE_BLOCK) to the cmd register. The internal DMA controller determines that a write data transfer needs to be performed.
  3. The host sets the required transmit threshold level in the tx_wmark field in the fifoth register.
  4. The internal DMA controller engine fetches the descriptor and checks the OWN bit. If the OWN bit is set to 0, the host owns the descriptor. In this case, the internal DMA controller enters the suspend state and asserts the Descriptor Unable interrupt. The host then needs to set the descriptor OWN bit to 1 and release the DMA controller by writing any value to the pldmnd register.
  5. The host must write the descriptor base address to the dbaddr register.
  6. The internal DMA controller waits for the Command Done (CD) bit in the rintsts register to be set to 1, with no errors from the BIU. This condition indicates that a transfer can be done.
  7. The internal DMA controller engine waits for a DMA interface request from BIU. The BIU divides each transfer into smaller chunks. Each chunk is an internal request to the DMA. This request is generated based on the transmit threshold value.
  8. The internal DMA controller fetches the transmit data from the data buffer in the system memory and transfers the data to the FIFO buffer in preparation for transmission to the card.
  9. When data spans across multiple descriptors, the internal DMA controller fetches the next descriptor and continues with its operation with the next descriptor. The Last Descriptor bit in the descriptor DES0 field indicates whether the data spans multiple descriptors or not.
  10. When data transmission is complete, status information is updated in the idsts register by setting the ti bit to 1, if enabled. Also, the OWN bit is set to 0 by the DMA controller by updating the DES0 field of the descriptor.