This version (02 Feb 2024 08:50) was approved by Ionut Podgoreanu.The Previously approved version (27 Feb 2023 12:17) is available.

High-Speed DMA Controller Peripheral

The AXI DMAC is a high-speed, high-throughput, general purpose DMA controller intended to be used to transfer data between system memory and other peripherals like high-speed converters.

Features

Supports multiple interface types
- AXI3/4 memory mapped
- AXI4 Streaming
- ADI FIFO interface
Zero-latency transfer switch-over architecture
- Allows continuous high-speed streaming
Cyclic transfers
2D transfers
Scatter-Gather transfers

Utilization

Detailed Utilization (Click to expand)

Device Family	LUTs	FFs
Intel Arria 10	TBD	TBD
Xilinx Artix 7	TBD	TBD
Xilinx Kintex 7	TBD	TBD
Xilinx Virtex 7	TBD	TBD

Files

Name	Description
axi_dmac.v	Verilog source for the peripheral.

Block Diagram

Synthesis Configuration Parameters

Name	Description	Default
`ID`	Instance identification number.	0
`DMA_DATA_WIDTH_SRC`	Data path width of the source interface in bits.	64
`DMA_DATA_WIDTH_DEST`	Data path width of the destination interface in bits.	64
`DMA_DATA_WIDTH_SG`	Data path width of the scatter-gather interface in bits.	64
`DMA_LENGTH_WIDTH`	Width of transfer length control register in bits. Limits length of the transfers to 2**`DMA_LENGTH_WIDTH`.	24
`DMA_2D_TRANSFER`	Enable support for 2D transfers.	0
`DMA_SG_TRANSFER`	Enable support for scatter-gather transfers.	0
`ASYNC_CLK_REQ_SRC`	Whether the request and source clock domains are asynchronous.	1
`ASYNC_CLK_SRC_DEST`	Whether the source and destination clock domains are asynchronous.	1
`ASYNC_CLK_DEST_REQ`	Whether the destination and request clock domains are asynchronous.	1
`ASYNC_CLK_REQ_SG`	Whether the request and scatter-gather clock domains are asynchronous.	1
`ASYNC_CLK_SRC_SG`	Whether the source and scatter-gather clock domains are asynchronous.	1
`ASYNC_CLK_DEST_SG`	Whether the destination and scatter-gather clock domains are asynchronous.	1
`AXI_SLICE_DEST`	Whether to insert an extra register slice on the source data path.	0
`AXI_SLICE_SRC`	Whether to insert an extra register slice on the destination data path.	0
`SYNC_TRANSFER_START`	Enable the transfer start synchronization feature.	0
`CYCLIC`	Enable support for Cyclic transfers.	1
`DMA_AXI_PROTOCOL_SRC`	AXI protocol version of the source interface (0 = AXI4, 1 = AXI3).	0
`DMA_AXI_PROTOCOL_DEST`	AXI protocol version of the destination interface (0 = AXI4, 1 = AXI3).	0
`DMA_AXI_PROTOCOL_SG`	AXI protocol version of the scatter-gather interface (0 = AXI4, 1 = AXI3).	0
`DMA_TYPE_SRC`	Interface type for the source interface (0 = AXI-MM, 1 = AXI-Streaming, 2 = ADI-FIFO).	2
`DMA_TYPE_DEST`	Interface type for the destination interface (0 = AXI-MM, 1 = AXI-Streaming, 2 = ADI-FIFO).	0
`DMA_AXI_ADDR_WIDTH`	Maximum address width for AXI interfaces.	32
`MAX_BYTES_PER_BURST`	Maximum size of bursts in bytes. Must be power of 2 in a range of 2 beats to 4096 bytes The size of the burst is limited by the largest burst that both source and destination supports. This depends on the selected protocol. For AXI3 the maximum beats per burst is 16, while for AXI4 is 256. For non AXI interfaces the maximum beats per burst is in theory unlimited but it is set to 1024 to provide a reasonable upper threshold. This limitation is done internally in the core.	128
`FIFO_SIZE`	Size of the store-and-forward memory in bursts. Size of a burst is defined by the `MAX_BYTES_PER_BURST` parameter. Must be power of 2 in the range of 2 to 32.	4
`DISABLE_DEBUG_REGISTERS`	Disable debug registers.	0
`ENABLE_DIAGNOSTICS_IF`	Add insight into internal operation of the core, for debug purposes only.	0

Signal and Interface Pins

Name	Type	Description
`s_axi_aclk`	Clock	All `s_axi` signals and `irq` are synchronous to this clock.
`s_axi_aresetn`	Synchronous active low reset	Resets the internal state of the peripheral.
`s_axi`	AXI4-Lite bus slave	Memory mapped AXI-lite bus that provides access to modules register map.
`irq`	Level-High Interrupt	Interrupt output of the module. Is asserted when at least one of the modules interrupt is pending and enabled.
`m_src_axi_aclk`	Clock	The `m_src_axi` interface is synchronous to this clock. Only present when `DMA_TYPE_SRC` parameter is set to AXI-MM (0).
`m_src_axi_aresetn`	Synchronous active low reset	Reset for the `m_src_axi` interface. Only present when `DMA_TYPE_SRC` parameter is set to AXI-MM (0).
`m_src_axi`	AXI3/AXI4 bus master	Only present when `DMA_TYPE_SRC` parameter is set to AXI-MM (0).
`m_dest_axi_aclk`	Clock	The `m_src_axi` interface is synchronous to this clock. Only present when `DMA_TYPE_DEST` parameter is set to AXI-MM (0).
`m_dest_axi_aresetn`	Synchronous active low reset	Reset for the `m_dest_axi` interface. Only present when `DMA_TYPE_DEST` parameter is set to AXI-MM (0).
`m_dest_axi`	AXI3/AXI4 bus master	Only present when `DMA_TYPE_DEST` parameter is set to AXI-MM (0).
`m_sg_axi_aclk`	Clock	The `m_sg_axi` interface is synchronous to this clock. Only present when `DMA_SG_TRANSFER` parameter is set.
`m_sg_axi_aresetn`	Synchronous active low reset	Reset for the `m_sg_axi` interface. Only present when `DMA_SG_TRANSFER` parameter is set.
`m_sg_axi`	AXI3/AXI4 bus master	Only present when `DMA_SG_TRANSFER` parameter is set.
`s_axis_aclk`	Clock	The `s_axis` interface is synchronous to this clock. Only present when `DMA_TYPE_SRC` parameter is set to AXI-Streaming (1).
`s_axis`	AXI-streaming bus slave	Only present when `DMA_TYPE_SRC` parameter is set to AXI-Streaming (1).
`m_axis_aclk`	Clock	The `m_axis` interface is synchronous to this clock. Only present when `DMA_TYPE_DEST` parameter is set to AXI-Streaming (1).
`m_axis`	AXI-streaming bus master	Only present when `DMA_TYPE_DEST` parameter is set to AXI-Streaming (1).
`fifo_wr_clk`	Clock	The `fifo_wr` interface is synchronous to this clock. Only present when `DMA_TYPE_SRC` parameter is set to FIFO (2).
`fifo_wr`	FIFO write interface	Only present when `DMA_TYPE_SRC` parameter is set to FIFO (2).
`fifo_rd_clk`	Clock	The `fifo_rd` interface is synchronous to this clock. Only present when `DMA_TYPE_DEST` parameter is set to FIFO (2).
`fifo_rd`	FIFO read interface	Only present when `DMA_TYPE_DEST` parameter is set to FIFO (2).
`dest_diag_level_bursts`	Diagnostics interface	Only present when `ENABLE_DIAGNOSTICS_IF` parameter is set .

Register Map

DMA Controller (axi_dmac)

Click to expand regmap

0x000	0x0000	VERSION				Version of the peripheral. Follows semantic versioning. Current version 4.05.61.
Address		Bits	Name	Type	Default	Description
DWORD	BYTE	Bits	Name	Type	Default	Description
		[31:16]	VERSION_MAJOR	RO	0x04
		[15:8]	VERSION_MINOR	RO	0x05
		[7:0]	VERSION_PATCH	RO	0x61
0x001	0x0004	PERIPHERAL_ID
		[31:0]	PERIPHERAL_ID	RO	`ID`	Value of the ID configuration parameter.
0x002	0x0008	SCRATCH
		[31:0]	SCRATCH	RW	0x00000000	Scratch register useful for debug.
0x003	0x000c	IDENTIFICATION
		[31:0]	IDENTIFICATION	RO	0x444D4143	Peripheral identification ('D', 'M', 'A', 'C').
0x004	0x0010	INTERFACE_DESCRIPTION
		[3:0]	BYTES_PER_BEAT_DEST_LOG2	R	log2(`DMA_DATA_WIDTH_DEST`/8)	Width of data bus on destination interface. Log2 of interface data widths in bytes.
		[5:4]	DMA_TYPE_DEST	R	`DMA_TYPE_DEST`	Value of `DMA_TYPE_DEST` parameter.(0 - AXI MemoryMap, 1 - AXI Stream, 2 - FIFO
		[11:8]	BYTES_PER_BEAT_SRC_LOG2	R	log2(`DMA_DATA_WIDTH_SRC`/8)	Width of data bus on source interface. Log2 of interface data widths in bytes.
		[13:12]	DMA_TYPE_SRC	R	`DMA_TYPE_SRC`	Value of `DMA_TYPE_SRC` parameter.(0 - AXI MemoryMap, 1 - AXI Stream, 2 - FIFO
		[19:16]	BYTES_PER_BURST_WIDTH	R	`BYTES_PER_BURST_WIDTH`	Value of `BYTES_PER_BURST_WIDTH` interface parameter. Log2 of the real `MAX_BYTES_PER_BURST`. The starting address of the transfer must be aligned with `MAX_BYTES_PER_BURST` to avoid crossing the 4kB address boundary.
0x020	0x0080	IRQ_MASK
		[1]	TRANSFER_COMPLETED	RW	0x1	Masks the TRANSFER_COMPLETED IRQ.
		[0]	TRANSFER_QUEUED	RW	0x1	Masks the TRANSFER_QUEUED IRQ.
0x021	0x0084	IRQ_PENDING
		[1]	TRANSFER_COMPLETED	RW1C	0x0	This bit will be asserted if a transfer has been completed and the TRANSFER_COMPLETED bit in the IRQ_MASK register is not set. Either if all bytes have been transferred or an error occurred during the transfer.
		[0]	TRANSFER_QUEUED	RW1C	0x0	This bit will be asserted if a transfer has been queued and it is possible to queue the next transfer. It can be masked out by setting the TRANSFER_QUEUED bit in the IRQ_MASK register.
0x022	0x0088	IRQ_SOURCE
		[1]	TRANSFER_COMPLETED	RO	0x0	This bit will be asserted if a transfer has been completed. Either if all bytes have been transferred or an error occurred during the transfer. Cleared together with the corresponding IRQ_PENDING bit.
		[0]	TRANSFER_QUEUED	RO	0x0	This bit will be asserted if a transfer has been queued and it is possible to queue the next transfer. Cleared together with the corresponding IRQ_PENDING bit.
0x100	0x0400	CONTROL
		[2]	HWDESC	RW	0x0	When set to 1 the scatter-gather transfers are enabled. Note, this field is only valid if the DMA channel has been configured with SG transfer support.
		[1]	PAUSE	RW	0x0	When set to 1 the currently active transfer is paused. It will be resumed once the bit is cleared again.
		[0]	ENABLE	RW	0x0	When set to 1 the DMA channel is enabled.
0x101	0x0404	TRANSFER_ID
		[1:0]	TRANSFER_ID	RO	0x00	This register contains the ID of the next transfer. The ID is generated by the DMAC and after the transfer has been started can be used to check if the transfer has finished by checking the corresponding bit in the TRANSFER_DONE register. The contents of this register is only valid if TRANSFER_SUBMIT is 0.
0x102	0x0408	TRANSFER_SUBMIT
		[0]	TRANSFER_SUBMIT	RW	0x0	Writing a 1 to this register queues a new transfer. The bit transitions back to 0 once the transfer has been queued or the DMA channel is disabled. Writing a 0 to this register has no effect.
0x103	0x040c	FLAGS
		[0]	CYCLIC	RW	`CYCLIC`	Setting this field to 1 puts the DMA transfer into cyclic mode. In cyclic mode the controller will re-start a transfer again once it has finished. In cyclic mode no end-of-transfer interrupts will be generated.
		[1]	TLAST	RW	0x1	When setting this bit for a MM to AXIS transfer the TLAST signal will be asserted during the last beat of the transfer. For AXIS to MM transfers the TLAST signal from the AXIS interface is monitored. After its occurrence all descriptors are ignored until this bit is set.
		[2]	PARTIAL_REPORTING_EN	RW	0x0	When setting this bit the length of partial transfers caused eventually by TLAST will be recorded.
0x104	0x0410	DEST_ADDRESS
		[31:0]	DEST_ADDRESS	RW	0x00000000	This register contains the destination address of the transfer. The address needs to be aligned to the bus width. This register is only valid if the DMA channel has been configured for write to memory support.
0x105	0x0414	SRC_ADDRESS
		[31:0]	SRC_ADDRESS	RW	0x00000000	This register contains the source address of the transfer. The address needs to be aligned to the bus width. This register is only valid if the DMA channel has been configured for read from memory support.
0x106	0x0418	X_LENGTH
		[23:0]	X_LENGTH	RW	{log2(max( `DMA_DATA_WIDTH_SRC`, `DMA_DATA_WIDTH_DEST` )/8){1'b1}}	Number of bytes to transfer - 1.
0x107	0x041c	Y_LENGTH
		[23:0]	Y_LENGTH	RW	0x000000	Number of rows to transfer - 1. Note, this field is only valid if the DMA channel has been configured with 2D transfer support.
0x108	0x0420	DEST_STRIDE
		[23:0]	DEST_STRIDE	RW	0x000000	The number of bytes between the start of one row and the next row for the destination address. Needs to be aligned to the bus width. Note, this field is only valid if the DMA channel has been configured with 2D transfer support and write to memory support.
0x109	0x0424	SRC_STRIDE
		[23:0]	SRC_STRIDE	RW	0x000000	The number of bytes between the start of one row and the next row for the source address. Needs to be aligned to the bus width. Note, this field is only valid if the DMA channel has been configured with 2D transfer and read from memory support.
0x10a	0x0428	TRANSFER_DONE				If bit x is set in this register the transfer with ID x has been completed. The bit will automatically be cleared when a new transfer with this ID is queued and will be set when the transfer has been completed.
		[0]	TRANSFER_0_DONE	RO	0x0	If this bit is set the transfer with ID 0 has been completed.
		[1]	TRANSFER_1_DONE	RO	0x0	If this bit is set the transfer with ID 1 has been completed.
		[2]	TRANSFER_2_DONE	RO	0x0	If this bit is set the transfer with ID 2 has been completed.
		[3]	TRANSFER_3_DONE	RO	0x0	If this bit is set the transfer with ID 3 has been completed.
		[31]	PARTIAL_TRANSFER_DONE	RO	0x0	If this bit is set at least one partial transfer was transferred. This field will reset when the ENABLE control bit is reset or when all information on partial transfers was read through PARTIAL_TRANSFER_LENGTH and PARTIAL_TRANSFER_ID registers.
0x10b	0x042c	ACTIVE_TRANSFER_ID
		[4:0]	ACTIVE_TRANSFER_ID	RO	0x00	ID of the currently active transfer. When no transfer is active this register will be equal to the TRANSFER_ID register.
0x10c	0x0430	STATUS
		[31:0]	RESERVED	RO	0x00000000	This register is reserved for future usage. Reading it will always return 0.
0x10d	0x0434	CURRENT_DEST_ADDRESS
		[31:0]	CURRENT_DEST_ADDRESS	RO	0x00000000	Address to which the next data sample is written to. This register is only valid if the DMA channel has been configured for write to memory support.
0x10e	0x0438	CURRENT_SRC_ADDRESS
		[31:0]	CURRENT_SRC_ADDRESS	RO	0x00000000	Address form which the next data sample is read. This register is only valid if the DMA channel has been configured for read from memory support.
0x112	0x0448	TRANSFER_PROGRESS
		[23:0]	TRANSFER_PROGRESS	RO	0x000000	This field presents the number of bytes transferred to the destination for the current transfer. This register will be cleared once the transfer completes. This should be used for debugging purposes only.
0x113	0x044c	PARTIAL_TRANSFER_LENGTH
		[31:0]	PARTIAL_LENGTH	RO	0x00000000	Length of the partial transfer in bytes. Represents the number of bytes received until the moment of TLAST assertion. This will be smaller than the programmed length from the X_LENGTH and Y_LENGTH registers.
0x114	0x0450	PARTIAL_TRANSFER_ID				Must be read after the PARTIAL_TRANSFER_LENGTH registers.
		[1:0]	PARTIAL_TRANSFER_ID	RO	0x0	ID of the transfer that was partial.
0x115	0x0454	DESCRIPTOR_ID
		[31:0]	DESCRIPTOR_ID	RO	0x00000000	ID of the descriptor that points to the current memory segment being transferred. If HWDESC is set to 0, then this register returns 0.
0x11f	0x047c	SG_ADDRESS
		[31:0]	SG_ADDRESS	RW	0x00000000	This register contains the starting address of the scatter-gather transfer. The address needs to be aligned to the bus width. This register is only valid if the DMA channel has been configured with SG transfer support.
0x124	0x0490	DEST_ADDRESS_HIGH
		[31:0]	DEST_ADDRESS_HIGH	RW	0x00000000	This register contains the HIGH segment of the destination address of the transfer. This register is only valid if the DMA_AXI_ADDR_WIDTH is bigger than 32 and if DMA channel has been configured for write to memory support.
0x125	0x0494	SRC_ADDRESS_HIGH
		[31:0]	SRC_ADDRESS_HIGH	RW	0x00000000	This register contains the HIGH segment of the source address of the transfer. This register is only valid if the DMA_AXI_ADDR_WIDTH is bigger than 32 and if the DMA channel has been configured for read from memory support.
0x126	0x0498	CURRENT_DEST_ADDRESS_HIGH
		[31:0]	CURRENT_DEST_ADDRESS_HIGH	RO	0x00000000	HIGH segment of the address to which the next data sample is written to. This register is only valid if the DMA_AXI_ADDR_WIDTH is bigger than 32 and if the DMA channel has been configured for write to memory support.
0x127	0x049c	CURRENT_SRC_ADDRESS_HIGH
		[31:0]	CURRENT_SRC_ADDRESS_HIGH	RO	0x00000000	HIGH segment of the address from which the next data sample is read. This register is only valid if the DMA_AXI_ADDR_WIDTH is bigger than 32 and if the DMA channel has been configured for read from memory support.
0x12f	0x04bc	SG_ADDRESS_HIGH
		[31:0]	SG_ADDRESS_HIGH	RW	0x00000000	HIGH segment of the starting address of the scatter-gather transfer. This register is only valid if the DMA_AXI_ADDR_WIDTH is bigger than 32 and if the DMA channel has been configured with SG transfer support.
Thu Feb 1 12:18:03 2024

Access Type	Name	Description
RO	Read-only	Reads will return the current register value. Writes have no effect.
RW	Read-write	Reads will return the current register value. Writes will change the current register value.
RW1C	Write-1-to-clear	Reads will return the current register value. Writing the register will clear those bits of the register which were set to 1 in the value written. Bits are set by hardware.
RW1S	Write-1-to-set	Reads will return the current register value. Writing the register will set those bits of the register which were set to 1 in the value written. Bits are cleared by hardware.
V	Volatile	The V suffix indicates that the register is volatile and its content might change without software interaction. The value of registers without the volatile designation will not change without an explicit write done by software.

Theory of Operation

HDL Synthesis Settings

Sizing of the internal store-and-forward data buffer

An internal buffer is used to store data from the source interface before it is forwarded to the destination once that can accept it. The purpose of the buffer is to even out the rate mismatches between the source and destination. e.g if the destination is a FIFO interface with a fixed data rate and the source is a MM interface, the intent is to keep the buffer as full as possible so in case of the MM interface is not ready data can be still provided to the destination without risking an underflow. Similarly in case the destination is a MM interface and the source a FIFO interface with a fixed data rate, the intent is to keep the buffer as empty as possible so in case the MM interface is not ready data can be still accepted from the source without risking an overflow.

The size of the buffer in bytes is determined by the synthesis parameters of the module and it is equal to FIFO_SIZE * MAX_BYTES_PER_BURST

Buffer dimensions

The width of the buffer is sized to be the largest width from the source and destination interfaces.

BUFFER_WIDTH_IN_BYTES = MAX(DMA_DATA_WIDTH_SRC,DMA_DATA_WIDTH_DEST)/8
BUFFER_DEPTH = FIFO_SIZE*MAX_BYTES_PER_BURST / BUFFER_WIDTH_IN_BYTES

Interfaces and Signals

Register Map Configuration Interface

The register map configuration interface can be accessed through the AXI4-Lite S_AXI interface. The interface is synchronous to the s_axi_aclk. The s_axi_aresetn signal is used to reset the peripheral and should be asserted during system startup until the s_axi_aclk is active and stable. De-assertion of the reset signal should by synchronous to s_axi_aclk.

Data Interfaces

AXI-Streaming slave

The interface back-pressures through the s_axis_ready signal. If the core is in the idle state the s_axis_ready signal will stay low until a descriptor is submitted. The s_axis_ready will go low once the internal buffer of the core is full. It will go high only after enough space is available to store at least a burst (MAX_BYTES_PER_BURST bytes); Once the current transfer is finished and a new descriptor was not submitted the s_axis_ready will go low. The s_axis_ready will go low also when the TLAST is used that asserts unexpectedly. Unexpectedly means that the transfer length defined by TLAST is shorter than the transfer length programmed in the descriptor (X_LENGTH register). If the next descriptor was already submitted the s_axis_ready will assert within few cycles, in other hand will stay low until a new descriptor is submitted.

The xfer_req is asserted once a transfer is submitted to the descriptor queue and stays high until all data from the current transfer is received/send through the AXI Stream/FIFO interface. If during the current transfer another descriptor is queued (submitted) it will stay high and so on.

Configuration Interface

The peripheral features a register map configuration interface that can be accessed through the AXI4-Lite S_AXI port. The register map can be used to configure the peripherals operational parameters, query the current status of the device and query the features supported by the device.

Peripheral Identification

The peripheral contains multiple registers that allow the identification of the peripheral as well as discovery of features that were configured at HDL synthesis time. Apart from the SCRATCH register all registers in this section are read only and writes to them will be ignored.

The VERSION (0x000) register contains the version of the peripheral. The version determines the register map layout and general features supported by the peripheral. The version number follows semantic versioning. Increments in the major number indicate backwards incompatible changes, increments in the minor number indicate backwards compatible changes, patch letter increments indicate fixed incorrect behavior.

The PERIPHERAL_ID (0x004) register contains the value of the ID HDL configuration parameter that was set during synthesis. Its primary function is to allow to distinguish between multiple instances of the peripheral in the same design.

The SCRATCH (0x008) register is a general purpose 32-bit register that can be set to an arbitrary values. Reading the register will yield the value previously written (The value will be cleared when the peripheral is reset). It's content does not affect the operation of the peripheral. It can be used by software to test whether the register map is accessible or store custom peripheral associated data.

The IDENTIFICATION (0x00c) register contains the value of “DMAC”. This value is unique to this type of peripheral and can be used to ensure that the peripheral exists at the expected location in the memory mapped IO register space.

Interrupt Handling

Interrupt processing is handled by three closely related registers. All three registers follow the same layout, each bit in the register corresponds to one particular interrupt.

When an interrupt event occurs it is recorded in the IRQ_SOURCE (0x088) register. For a recorded interrupt event the corresponding bit is set to 1. If an interrupt event occurs while the bit is already set to 1 it will stay set to 1.

The IRQ_MASK (0x080) register controls how recorded interrupt events propagate. An interrupt is considered to be enabled if the corresponding bit in the IRQ_MASK register is set to 0, it is considered to be disabled if the bit is set to 1.

Disabling an interrupt will not prevent it from being recorded, but only its propagation. This means if an interrupt event was previously recorded while the interrupt was disabled and the interrupt is being enabled the interrupt event will then propagate.

An interrupt event that has been recorded and is enabled propagates to the IRQ_PENDING (0x084) register. The corresponding bit for such an interrupt will read as 1. Disabled or interrupts for which no events have been recorded will read as 0. Also if at least one interrupt has been recorded and is enabled the external irq signal will be asserted to signal the IRQ event to the upstream IRQ controller.

A recorded interrupt event can be cleared (or acknowledged) by writing a 1 to the corresponding bit to either the IRQ_SOURCE or IRQ_PENDING register. It is possible to clear multiple interrupt events at the same time by setting multiple bits in a single write operation.

For more details regarding interrupt operation see the interrupts section of this document.

Transfer Configuration

The DEST_ADDRESS (0x410) register contains the destination address of the transfer. The address must be aligned to the destination bus width. Non-aligned addresses will be automatically aligned internally by setting the LSBs to 0. This register is only valid if the DMA channel has been configured for write to memory support.

The SRC_ADDRESS (0x414) register contains the source address of the transfer. The address must be aligned to the source bus width. Non-aligned addresses will be automatically aligned internally by setting the LSBs to 0. This register is only valid if the DMA channel has been configured for write from memory support.

The X_LENGTH (0x418) register contains the number of bytes to transfer per row. The number of bytes is equal to the value of the register + 1 (E.g. a value of 0x3ff means 0x400 bytes).

The Y_LENGTH (0x41C) register contains the number of rows to transfer. The number of rows is equal to the value of the register + 1 (E.g. a value of 1079 means 1080 rows). This register is only valid if the DMA channel has been configured with 2D transfer support. If 2D transfer support is disabled the number of rows is always 1 per transfer.

The SRC_STRIDE (0x424) and DEST_STRIDE (0x420) registers contain the number of bytes between the start of one row and the next row. Needs to be aligned to the bus width. This field is only valid if the DMA channel has been configured with 2D transfer support.

The total number of bytes transferred is equal to (X_LENGTH + 1) * (Y_LENGTH + 1).

The FLAGS (0x40C) register controls the behavior of the transfer.

If the CYCLIC ([0]) bit is set the transfer will run in cyclic mode.
If the TLAST ([1]) bit is set the TLAST signal will be asserted during the last beat of the AXI Stream transfer.

Transfer Submission

Writing a 1 to the TRANSFER_SUBMIT (0x408) register queues a new transfer. If the internal transfer queue is full the TRANSFER_SUBMIT bit will stay asserted until room becomes available, the bit transitions back to 0 once the transfer has been queued. Writing a 0 to this register has no effect. Writing a 1 to the register while it is already 1 will also have no effect. When submitting a new transfer software should always check that the TRANSFER_SUBMIT [0] bit is 0 before setting it, otherwise the transfer will not be queued.

If the DMA channel is disabled (ENABLE control bit is set to 0) while a queuing operation is in progress it will be aborted and the TRANSFER_SUBMIT bit will de-assert.

The TRANSFER_ID (0x404) register contains the ID of the next transfer. The ID is generated by the DMA controller and can be used to check if a transfer has been completed by checking the corresponding bit in the TRANSFER_DONE (0x428) register. The contents of this register is only valid if TRANSFER_SUBMIT is 0. Software should read this register before asserting the TRANSFER_SUBMIT bit.

Transfer Status

The TRANSFER_DONE (0x428) register indicates whether a submitted transfer has been completed. Each bit in the register corresponds to transfer ID. When a new transfer is submitted the corresponding bit in the register is cleared, once the the transfer has been completed the corresponding bit will be set.

The ACTIVE_TRANSFER_ID (0x42C) register holds the ID of the currently active transfer. When no transfer is active the value of register will be equal to the value of the TRANSFER_ID (0x404) register.

Transfer length reporting

When using MM or FIFO source interfaces the amount of data which the core will transfer is defined by X_LENGTH and Y_LENGTH registers in the moment of the transfer submission. Once the corresponding bit from the TRANSFER_DONE is set the programmed amount of data is transferred.

When using streaming interface (AXIS) as source, the length of transfers will be defined by the assertion of TLAST signal which is unknown at the moment of transfer submission. In this case X_LENGTH and Y_LENGTH specified during the transfer submission will act as upper limits for the transfer. Transfers where the TLAST occurs ahead of programmed length will be noted as partial transfers. If PARTIAL_REPORTING_EN bit from the FLAGS register is set, the length of partial transfers will be recorded and exposed through the PARTIAL_TRANSFER_LENGTH and PARTIAL_TRANSFER_ID registers. The availability of information regarding partial transfers is done through the PARTIAL_TRANSFER_DONE field of TRANSFER_DONE register.

During operation the TRANSFER_PROGRESS register can be consulted to check the progress of the current transfer. The register presents the number of bytes the destination accepted during the in progress transfer. This register will be cleared once the transfer completes. This register should be used for debugging purposes only.

Transfer Tear-down

Non-cyclic transfers stop once the programmed amount of data is transferred to the destination. Cyclic transfers needs to be stopped with software intervention by setting the ENABLE control bit to 0. In case if required, non cyclic transfers can be interrupted in the same way. The transfer tear down is done gracefully and is done at a burst resolution on MM interfaces and beat resolution on non-MM interfaces. DMAC shuts down gracefully as fast as possible while completing all in-progress MM transactions.

Source side: For MM interface once the ENABLE bit de-asserts the DMAC won't issue new requests towards the source interface but will wait until all pending requests are fulfilled by the source. For non-MM interfaces, once the ENABLE bit de-asserts the DMAC will stop to accept new data. This will lead to partial bursts in the internal buffer but this data will be cleared/lost once the destination side completes all pending bursts.

Destination side: For MM interface the DMAC will complete all pending requests that have been started by issuing the address. For non-MM interfaces once the ENABLE bit de-asserts the DMAC will stop to drive new data. All the data from the internal buffer will be cleared/lost. In case of AXIS the DMAC will wait for data to be accepted if valid is high since it can't just de-assert valid without breaking the interface semantics

Interrupts

The DMA controller supports interrupts to allow asynchronous notification of certain events to the CPU. This can be used as an alternative to busy-polling the status registers. Two types of interrupt events are implemented by the DMA controller.

The TRANSFER_QUEUED interrupt is asserted when a transfer is moved from the register map to the internal transfer queue. This is equivalent to the TRANSFER_SUBMIT register transitioning from 1 to 0. Software can use this interrupt as an indication that the next transfer can be submitted.

Note that a transfer being queued does not mean that it has been started yet. If other transfers are already queued those will be processed first.

The TRANSFER_COMPLETED interrupt is asserted when a previously submitted transfer has been completed. To find out which transfer has been completed the TRANSFER_DONE register should be checked.

Note that depending on the transfer size and interrupt latency it is possible for multiple transfers to complete before the interrupt handler runs. In that case the interrupt handler will only run once. Software should always check all submitted transfers for completion.

2D Transfers

If the DMA_2D_TRANSFER HDL synthesis configuration parameter is set the DMA controller has support for 2D transfers.

A 2D transfer is composed of a number of rows with each row containing a certain number of bytes. Between each row there might be a certain amount of padding bytes that are skipped by the DMA.

For 2D transfers the X_LENGTH register configures the number of bytes per row and the Y_LENGTH register configures the number of rows. The SRC_STRIDE and DEST_STRIDE registers configure the number of bytes in between start of two rows.

E.g. the first row will start at the configured source or destination address, the second row will start at the configured source or destination address plus the stride and so on.

ROW_SRC_ADDRESS = SRC_ADDRESS + SRC_STRIDE * N
ROW_DEST_ADDRESS = DEST_ADDRESS + DEST_STRIDE * N

If support for 2D transfers is disabled only the X_LENGTH register is considered and the number of rows per transfer is fixed to 1.

Cyclic Transfers

If the CYCLIC HDL synthesis configuration parameter is set the DMA controller has support for cyclic transfers.

A cyclic transfer once completed will restart automatically with the same configuration. The behavior of cyclic transfer is equivalent to submitting the same transfer over and over again, but generates less software management overhead.

A transfer is cyclic if the CYCLIC ([0]) bit of the FLAGS (0x40C) is set to 1 during transfer submission.

For cyclic transfers no end-of-transfer interrupts will be generated. To stop a cyclic transfer the DMA channel must be disabled.

Any additional transfers that are submitted after the submission of a cyclic transfer (and before stopping the cyclic transfer) will never be executed.

Scatter-Gather Transfers

If the DMA_SG_TRANSFER HDL synthesis configuration parameter is set the DMA controller has support for scatter-gather transfers.

The scatter-gather optional feature allows the DMA to access noncontiguous areas of memory within a single transfer.

The DMA can read from or write to different memory addresses in one transaction by using a list of vectors called descriptors. Each descriptor provides the starting address and the length of the current memory block to be accessed, as well as the next address of the following descriptor to be processed. By chaining these descriptors, the DMA can gather the data into a contiguous transfer from the scattered memory data from multiple addresses.

The scatter-gather has its own dedicated AXI3/4 memory mapped interface m_sg_axi through which it receives the descriptor data.

Descriptor Structure

The scatter-gather interface fetches the descriptor information from memory in the following order:

Size	Name	Description
32-bit	flags	This field includes 2 control bits: * bit0: if set, the transfer will complete after this last descriptor is processed, and the DMA core will go back to idle state; if cleared, the next DMA descriptor pointed to by `next_sg_addr` will be loaded. * bit1: if set, an end-of-transfer interrupt will be raised after the memory segment pointed to by this descriptor has been transferred.
32-bit	id	This field corresponds to an identifier of the descriptor.
64-bit	dest_addr	This field contains the destination address of the transfer.
64-bit	src_addr	This field contains the source address of the transfer.
64-bit	next_sg_addr	This field contains the address of the next descriptor.
32-bit	y_len	This field contains the number of rows to transfer, minus one.
32-bit	x_len	This field contains the number of bytes to transfer, minus one.
32-bit	src_stride	This field contains the number of bytes between the start of one row and the next row for the source address.
32-bit	dst_stride	This field contains the number of bytes between the start of one row and the next row for the destination address.

The y_len, src_stride and dst_stride fields are only useful for 2D transfers and should be set to 0 if 2D transfers are not required.

Transfer Configuration

The scatter-gather transfers are enabled through the HWDESC bit from the CONTROL (0x400) register. Once this bit is set, cyclic transfers are disabled.

To start a scatter-gather transfer, the address of the first DMA descriptor must be written to the register pair [SG_ADDRESS_HIGH(0x4BC), SG_ADDRESS(0x47C)].

To end a scatter-gather transfer, the last descriptor of the transfer must have the flags[0] bit set.

The scatter-gather transfer is queued in a similar way to the simple transfers, through the TRANSFER_SUBMIT. Software should always poll this bit to be 0 before setting it, otherwise the scatter-gather transfer will not be queued.

The scatter-gather transfers support the generation of the same two types of interrupt events as the simple transfers. However, the scatter-gather transfers have the distinct advantage of generating fewer interrupts by treating the chained descriptor transfers as a single transfer, thus improving the performance of the application.

Transfer Start Synchronization

If the transfer start synchronization feature of the DMA controller is enabled the start of a transfer is synchronized to a flag in the data stream. This is primarily useful if the data stream does not have any back-pressure and one unit of data spans multiple beats (e.g. packetized data). This ensures that the data is properly aligned to the beginning of the memory buffer.

Data that is received before the synchronization flag is asserted will be ignored by the DMA controller.

For the FIFO write interface the fifo_wr_sync signal is the synchronization flag signal. For the AXI-Streaming interface the synchronization flag is carried in s_axis_user[0]. In both cases the synchronization flag is qualified by the same control signal as the data.

Diagnostics interface

For debug purposes a diagnostics interface is added to the core.
The dest_diag_level_bursts signal adds insight into the fullness of the internal memory buffer during operation. The information is exposed in number of bursts where the size of a burst is defined by the MAX_BYTES_PER_BURST parameter. The value of dest_diag_level_bursts increments for each burst accumulated in the DMACs internal buffer. It decrements once the burst leaves the DMAC on its destination port. The signal is synchronous to the destination clock domain (m_dest_axi_aclk or m_axis_aclk depending on DMA_TYPE_DEST).

Limitations

AXI 4kByte Address Boundary

Software must program the SRC_ADDRESS and DEST_ADDRESS registers in such way that AXI burst won't cross the 4kB address boundary. The following condition must hold:

MAX_BYTES_PER_BURST ≤ 4096;
MAX_BYTES_PER_BURST is power of 2;
SRC/DEST_ADDRESS mod MAX_BYTES_PER_BURST == 0
SRC/DEST_ADDRESS[11:0] + MIN(X_LENGTH+1,MAX_BYTES_PER_BURST) ≤ 4096

Address Alignment

Software must program the SRC_ADDRESS and DEST_ADDRESSregisters to be multiple of the corresponding MM data bus. The following conditions must hold:

SRC_ADDRESS MOD (DMA_DATA_WIDTH_SRC/8) == 0
DEST_ADDRESS MOD (DMA_DATA_WIDTH_DEST/8) == 0

Transfer Length Alignment

Software must program the X_LENGTH register to be multiple of the widest data bus. The following condition must hold:

(X_LENGTH+1) MOD MAX(DMA_DATA_WIDTH_SRC, DMA_DATA_WIDTH_DEST)/8 == 0

This restriction can be relaxed for the memory mapped interfaces. This is done by partially ignoring data of a beat from/to the MM interface:

For write access the strobe bits are used to mask out bytes that do not contain valid data.
For read access a full beat is read but part of the data is discarded. This works fine as long as the read access is side effect free. I.e. this method should not be used to access data from memory mapped peripherals like a FIFO.

E.g. the length alignment requirement of a DMA configured for a 64-bit memory mapped interface and a 16-bit streaming interface is only 2 bytes instead of 8 bytes.

Note that the address alignment requirement is not affected by this. The address still needs to be aligned to the width of the MM interface that it belongs to.

Scatter-Gather Datapath Width

The scatter-gather dedicated interface m_sg_axi currently supports only 64-bit transfers. DMA_DATA_WIDTH_SG can only be set to 64.

Software Support

Analog Devices recommends to use the provided software drivers.

Analog Device AXI-DMAC DMA Controller Linux Driver

Known Issues

1. When max bytes per burst matches the data width of destination interface an erroneous extra beat is inserted after every valid beat on the destination side. Example configuration:

- axi mm → axi stream

- max bytes per burst = 128

- destination width = 1024 bits

Workaround: increase the max bytes per burst to larger than 128

Technical Support

Analog Devices will provide limited online support for anyone using the core with Analog Devices components (ADC, DAC, Video, Audio, etc) via the EngineerZone.

Glossary

Term	Description
beat	Represents the amount of data that is transferred in one clock cycle.
burst	Represents the amount of data that is transferred in a group of consecutive beats.
partial transfer	Represents a transfer which is shorter than the programmed length that is based on the X_LENGTH and Y_LENGTH registers. This can occur on AXIS source interfaces when TLAST asserts earlier than the programmed length.

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Analog Devices Wiki

Table of Contents

High-Speed DMA Controller Peripheral

Features

Utilization

Files

Block Diagram

Synthesis Configuration Parameters

Signal and Interface Pins

Register Map

DMA Controller (axi_dmac)

Theory of Operation

HDL Synthesis Settings

Sizing of the internal store-and-forward data buffer

Interfaces and Signals

Register Map Configuration Interface

Data Interfaces

AXI-Streaming slave

Configuration Interface

Peripheral Identification

Interrupt Handling

Transfer Configuration

Transfer Submission

Transfer Status

Transfer length reporting

Transfer Tear-down

Interrupts

2D Transfers

Cyclic Transfers

Scatter-Gather Transfers

Descriptor Structure

Transfer Configuration

Transfer Start Synchronization

Diagnostics interface

Limitations

AXI 4kByte Address Boundary

Address Alignment

Transfer Length Alignment

Scatter-Gather Datapath Width

Software Support

Known Issues

Technical Support

Glossary

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