MM2S_DMACR (MM2S DMA Control Register – Offset 00h) - 7.1 English

AXI DMA v7.1 LogiCORE IP Product Guide (PG021)

Document ID
PG021
Release Date
2024-06-20
Version
7.1 English

This register provides control for the Memory Map to Stream DMA Channel.

Figure 1. MM2S DMACR Register

Table 1. MM2S_DMACR Register Details
Bits Field Name Default Value Access Type Description
0 RS 0 R/W Run/Stop control for controlling running and stopping of the DMA channel.
  • 0 = Stop – DMA stops when current (if any) DMA operations are complete. For Scatter/Gather Mode pending commands/transfers are flushed or completed. AXI4-Stream outs are potentially terminated early. Descriptors in the update queue are allowed to finish updating to remote memory before engine halt.

    For Direct Register mode pending commands/transfers are flushed or completed. AXI4-Stream outs are potentially terminated.

    The halted bit in the DMA Status register asserts to 1 when the DMA engine is halted. This bit is cleared by AXI DMA hardware when an error occurs. The CPU can also choose to clear this bit to stop DMA operations.

  • 1 = Run – Start DMA operations. The halted bit in the DMA Status register deasserts to 0 when the DMA engine begins operations.
1 Reserved 1 RO Writing to this bit has no effect and is always read as 1.
2 Reset 0 R/W Soft reset for resetting the AXI DMA core. Setting this bit to a 1 causes the AXI DMA to be reset. Reset is accomplished gracefully. Pending commands/transfers are flushed or completed.

AXI4-Stream outs are potentially terminated early. Setting either MM2S_DMACR.Reset = 1 or S2MM_DMACR. Reset = 1 resets the entire AXI DMA engine. After completion of a soft reset, all registers and bits are in the Reset State.

  • 0 = Normal operation.
  • 1 = Reset in progress.
3 Keyhole 0 R/W Keyhole Read. Setting this bit to 1 causes AXI DMA to initiate MM2S reads (AXI4 read) in non-incrementing address mode (Fixed Address Burst transfer on AXI4). This bit can be updated when AXI DMA is in idle. When using keyhole operation the Max Burst Length should not exceed 16. This bit should not be set when DRE is enabled.

This bit is non functional when the multichannel feature is enabled or in Direct Register mode.

4 Cyclic BD Enable 0 R/W When set to 1, the DMA operates in Cyclic Buffer Descriptor (BD) mode without any user intervention. In this mode, the Scatter Gather module ignores the 'Completed' bit of the BD. With this bit set, you can use the same BDs in cyclic manner without worrying about any stale descriptor errors.

This bit should be set/unset only when the DMA is idle or when not running. Updating this bit while the DMA is running can result in unexpected behavior.

This bit is non functional when DMA operates in multichannel mode.

11 to 5 Reserved 0 RO Writing to these bits has no effect, and they are always read as zeros.
1 IOC_IrqEn 0 R/W Interrupt on Complete (IOC) Interrupt Enable. When set to 1, allows DMASR.IOC_Irq to generate an interrupt out for descriptors with the IOC bit set.
  • 0 = IOC Interrupt disabled
  • 1 = IOC Interrupt enabled
13 Dly_IrqEn 0 R/W Interrupt on Delay Timer Interrupt Enable. When set to 1, allows DMASR.Dly_Irq to generate an interrupt out.
  • 0 = Delay Interrupt disabled
  • 1 = Delay Interrupt enabled
Note: This bit is ignored when AXI DMA is configured for Direct Register Mode.
14 Err_IrqEn 0 R/W Interrupt on Error Interrupt Enable.
  • 0 = Error Interrupt disabled
  • 1 = Error Interrupt enabled
15 Reserved 0 RO Writing to this bit has no effect and it is always read as zeros.
23 to 16 IRQ Threshold 01h R/W Interrupt Threshold. This value is used for setting the interrupt threshold. When IOC interrupt events occur, an internal counter counts down from the Interrupt Threshold setting. When the count reaches zero, an interrupt out is generated by the DMA engine.
Note: The minimum setting for the threshold is 0x01. A write of 0x00 to this register has no effect.
Note: This field is ignored when AXI DMA is configured for Direct Register Mode.
31 to 24 IRQ Delay 00h R/W Interrupt Delay Time Out. This value is used for setting the interrupt timeout value. The interrupt timeout mechanism causes the DMA engine to generate an interrupt after the delay time period has expired. Timer begins counting at the end of a packet and resets with receipt of a new packet or a timeout event occurs.

1 Timeout Interval = 125´ (clock period of SG clock)

Setting a value of 3 here results in a delay timeout of 125 x 3 x (clock period of SG clock).

Note: Setting this value to zero disables the delay timer interrupt.
Note: This field is ignored when AXI DMA is configured for Direct Register Mode.