DMA - Direct Memory Access

Description

Direct Memory Access (DMA) Peripheral API.

DMA access functions provide basic support for the following types of DMA cycles:

  • Basic , used for transferring data between memory and peripherals.
  • Auto-request , used for transferring data between memory locations.
  • Ping-pong , used for for continuous transfer of data between memory and peripherals, automatically toggling between primary and alternate descriptors.
  • Memory scatter-gather , used for transferring a number of buffers between memory locations.
  • Peripheral scatter-gather , used for transferring a number of buffers between memory and peripherals.

A basic understanding of the DMA controller is assumed. See the reference manual for more details.

The term 'descriptor' is synonymous to the 'channel control data structure' term.

To use the DMA controller, the initialization function must have been executed once (normally during the system initialization):

* DMA_Init();
* 

Normally, a DMA channel is configured:

* DMA_CfgChannel();
* 

The channel configuration only has to be done once if reusing the channel for the same purpose later.

To set up a DMA cycle, the primary and/or alternate descriptor has to be set up as indicated below.

For basic or auto-request cycles, use once on either primary or alternate descriptor:

* DMA_CfgDescr();
* 

For ping-pong cycles, configure both primary or alternate descriptors:

* DMA_CfgDescr(); // Primary descriptor config
* DMA_CfgDescr(); // Alternate descriptor config
* 

For scatter-gather cycles, program the alternate descriptor array:

* // 'n' is the number of scattered buffers
* // 'descr' points to the start of the alternate descriptor array
*
* // Fill in 'cfg'
* DMA_CfgDescrScatterGather(descr, 0, cfg);
* // Fill in 'cfg'
* DMA_CfgDescrScatterGather(descr, 1, cfg);
* :
* // Fill in 'cfg'
* DMA_CfgDescrScatterGather(descr, n - 1, cfg);
* 

In many cases, the descriptor configuration only has to be done once if re-using the channel for the same type of DMA cycles later.

To activate the DMA cycle, use the respective DMA_Activate...() function.

For ping-pong DMA cycles, use DMA_RefreshPingPong() from the callback to prepare the completed descriptor for reuse. Notice that the refresh must be done prior to the other active descriptor completes, otherwise the ping-pong DMA cycle will halt.

Data Structures

struct DMA_CB_TypeDef
Callback structure that can be used to define DMA complete actions.
struct DMA_CfgChannel_TypeDef
Configuration structure for a channel.
struct DMA_CfgDescr_TypeDef
Configuration structure for primary or alternate descriptor (not used for scatter-gather DMA cycles).
struct DMA_CfgDescrSGAlt_TypeDef
Configuration structure for alternate scatter-gather descriptor.
struct DMA_Init_TypeDef
DMA initialization structure.

Functions

void DMA_ActivateAuto (unsigned int channel, bool primary, void *dst, const void *src, unsigned int nMinus1)
Activate the DMA auto-request cycle (used for memory-memory transfers).
void DMA_ActivateBasic (unsigned int channel, bool primary, bool useBurst, void *dst, const void *src, unsigned int nMinus1)
Activate the DMA basic cycle (used for memory-peripheral transfers).
void DMA_ActivatePingPong (unsigned int channel, bool useBurst, void *primDst, const void *primSrc, unsigned int primNMinus1, void *altDst, const void *altSrc, unsigned int altNMinus1)
Activate a DMA ping-pong cycle (used for memory-peripheral transfers).
void DMA_ActivateScatterGather (unsigned int channel, bool useBurst, DMA_DESCRIPTOR_TypeDef *altDescr, unsigned int count)
Activate the DMA scatter-gather cycle (used for either memory-peripheral or memory-memory transfers).
void DMA_CfgChannel (unsigned int channel, DMA_CfgChannel_TypeDef *cfg)
Configure a DMA channel.
void DMA_CfgDescr (unsigned int channel, bool primary, DMA_CfgDescr_TypeDef *cfg)
Configure the DMA descriptor for auto-request, basic, or ping-pong DMA cycles.
void DMA_CfgDescrScatterGather (DMA_DESCRIPTOR_TypeDef *descr, unsigned int indx, DMA_CfgDescrSGAlt_TypeDef *cfg)
Configure an alternate DMA descriptor for use with scatter-gather DMA cycles.
void DMA_ChannelEnable (unsigned int channel, bool enable)
Enable or disable a DMA channel.
bool DMA_ChannelEnabled (unsigned int channel)
Check if the DMA channel is enabled.
void DMA_ChannelRequestEnable (unsigned int channel, bool enable)
Enable or disable a DMA channel request.
void DMA_Init ( DMA_Init_TypeDef *init)
Initialize the DMA controller.
void DMA_IRQHandler (void)
Interrupt handler for the DMA cycle completion handling.
void DMA_RefreshPingPong (unsigned int channel, bool primary, bool useBurst, void *dst, const void *src, unsigned int nMinus1, bool stop)
Refresh a descriptor used in a DMA ping-pong cycle.
void DMA_Reset (void)
Reset the DMA controller.
void DMA_IntClear (uint32_t flags)
Clear one or more pending DMA interrupts.
void DMA_IntDisable (uint32_t flags)
Disable one or more DMA interrupts.
void DMA_IntEnable (uint32_t flags)
Enable one or more DMA interrupts.
uint32_t DMA_IntGet (void)
Get pending DMA interrupt flags.
uint32_t DMA_IntGetEnabled (void)
Get enabled and pending DMA interrupt flags.
void DMA_IntSet (uint32_t flags)
Set one or more pending DMA interrupts.

Typedefs

typedef void(* DMA_FuncPtr_TypeDef ) (unsigned int channel, bool primary, void *user)
DMA interrupt callback function pointer.

Enumerations

enum DMA_DataInc_TypeDef {
dmaDataInc1 = _DMA_CTRL_SRC_INC_BYTE,
dmaDataInc2 = _DMA_CTRL_SRC_INC_HALFWORD,
dmaDataInc4 = _DMA_CTRL_SRC_INC_WORD,
dmaDataIncNone = _DMA_CTRL_SRC_INC_NONE
}
Amount source/destination address should be incremented for each data transfer.
enum DMA_DataSize_TypeDef {
dmaDataSize1 = _DMA_CTRL_SRC_SIZE_BYTE,
dmaDataSize2 = _DMA_CTRL_SRC_SIZE_HALFWORD,
dmaDataSize4 = _DMA_CTRL_SRC_SIZE_WORD
}
Data sizes (in number of bytes) to be read/written by DMA transfer.
enum DMA_CycleCtrl_TypeDef {
dmaCycleCtrlBasic = _DMA_CTRL_CYCLE_CTRL_BASIC,
dmaCycleCtrlAuto = _DMA_CTRL_CYCLE_CTRL_AUTO,
dmaCycleCtrlPingPong = _DMA_CTRL_CYCLE_CTRL_PINGPONG,
dmaCycleCtrlMemScatterGather = _DMA_CTRL_CYCLE_CTRL_MEM_SCATTER_GATHER,
dmaCycleCtrlPerScatterGather = _DMA_CTRL_CYCLE_CTRL_PER_SCATTER_GATHER
}
Types of DMA transfer.
enum DMA_ArbiterConfig_TypeDef {
dmaArbitrate1 = _DMA_CTRL_R_POWER_1,
dmaArbitrate2 = _DMA_CTRL_R_POWER_2,
dmaArbitrate4 = _DMA_CTRL_R_POWER_4,
dmaArbitrate8 = _DMA_CTRL_R_POWER_8,
dmaArbitrate16 = _DMA_CTRL_R_POWER_16,
dmaArbitrate32 = _DMA_CTRL_R_POWER_32,
dmaArbitrate64 = _DMA_CTRL_R_POWER_64,
dmaArbitrate128 = _DMA_CTRL_R_POWER_128,
dmaArbitrate256 = _DMA_CTRL_R_POWER_256,
dmaArbitrate512 = _DMA_CTRL_R_POWER_512,
dmaArbitrate1024 = _DMA_CTRL_R_POWER_1024
}
Number of transfers before controller does new arbitration.

Function Documentation

DMA_ActivateAuto()

void DMA_ActivateAuto ( unsigned int channel,
bool primary,
void * dst,
const void * src,
unsigned int nMinus1
)

Activate the DMA auto-request cycle (used for memory-memory transfers).

Prior to activating the DMA cycle, the channel and descriptor to be used must have been properly configured.

Note
If using this function on a channel already activated and in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to activate the DMA cycle for.
[in] primary
  • true - activate using the primary descriptor
  • false - activate using an alternate descriptor
[in] dst An ddress to a start location to transfer data to. If NULL, leave setting in descriptor as is from a previous activation.
[in] src An address to a start location to transfer data from. If NULL, leave setting in descriptor as is from a previous activation.
[in] nMinus1 A number of DMA transfer elements (minus 1) to transfer (<= 1023). The size of the DMA transfer element (1, 2 or 4 bytes) is configured with DMA_CfgDescr() .

DMA_ActivateBasic()

void DMA_ActivateBasic ( unsigned int channel,
bool primary,
bool useBurst,
void * dst,
const void * src,
unsigned int nMinus1
)

Activate the DMA basic cycle (used for memory-peripheral transfers).

Prior to activating the DMA cycle, the channel and descriptor to be used must have been properly configured.

Note
If using this function on a channel already activated and in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to activate the DMA cycle for.
[in] primary
  • true - activate using the primary descriptor
  • false - activate using an alternate descriptor
[in] useBurst The burst feature is only used on peripherals supporting DMA bursts. Bursts must not be used if the total length (as given by nMinus1) is less than the arbitration rate configured for the descriptor. See the reference manual for more details on burst usage.
[in] dst An address to a start location to transfer data to. If NULL, leave setting in descriptor as is from a previous activation.
[in] src An address to a start location to transfer data from. If NULL, leave setting in descriptor as is from a previous activation.
[in] nMinus1 A number of DMA transfer elements (minus 1) to transfer (<= 1023). The size of the DMA transfer element (1, 2 or 4 bytes) is configured with DMA_CfgDescr() .

DMA_ActivatePingPong()

void DMA_ActivatePingPong ( unsigned int channel,
bool useBurst,
void * primDst,
const void * primSrc,
unsigned int primNMinus1,
void * altDst,
const void * altSrc,
unsigned int altNMinus1
)

Activate a DMA ping-pong cycle (used for memory-peripheral transfers).

Prior to activating the DMA cycle, the channel and both descriptors must have been properly configured. The primary descriptor is always the first descriptor to be used by the DMA controller.

Note
If using this function on a channel already activated and in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to activate DMA cycle for.
[in] useBurst The burst feature is only used on peripherals supporting DMA bursts. Bursts must not be used if the total length (as given by nMinus1) is less than the arbitration rate configured for the descriptors. See the reference manual for more details on burst usage. Notice that this setting is used for both the primary and alternate descriptors.
[in] primDst An address to a start location to transfer data to, for the primary descriptor. If NULL, leave setting in descriptor as is from a previous activation.
[in] primSrc An address to a start location to transfer data from, for the primary descriptor. If NULL, leave setting in the descriptor as is from a previous activation.
[in] primNMinus1 A number of DMA transfer elements (minus 1) to transfer (<= 1023), for primary descriptor. The size of the DMA transfer element (1, 2 or 4 bytes) is configured with DMA_CfgDescr() .
[in] altDst An address to a start location to transfer data to, for an alternate descriptor. If NULL, leave setting in descriptor as is from a previous activation.
[in] altSrc An address to a start location to transfer data from, for an alternate descriptor. If NULL, leave setting in descriptor as is from a previous activation.
[in] altNMinus1 A number of DMA transfer elements (minus 1) to transfer (<= 1023), for an alternate descriptor. The size of the DMA transfer element (1, 2 or 4 bytes) is configured with DMA_CfgDescr() .

DMA_ActivateScatterGather()

void DMA_ActivateScatterGather ( unsigned int channel,
bool useBurst,
DMA_DESCRIPTOR_TypeDef * altDescr,
unsigned int count
)

Activate the DMA scatter-gather cycle (used for either memory-peripheral or memory-memory transfers).

Prior to activating the DMA cycle, the array with alternate descriptors must have been properly configured. This function can be reused without reconfiguring the alternate descriptors, as long as count is the same.

Note
If using this function on a channel already activated and in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to activate DMA cycle for.
[in] useBurst The burst feature is only used on peripherals supporting DMA bursts (this parameter is ignored for memory scatter-gather cycles). This parameter determines if bursts should be enabled during DMA transfers using the alternate descriptors. Bursts must not be used if the total length (as given by nMinus1 for the alternate descriptor) is less than the arbitration rate configured for the descriptor. See the reference manual for more details on burst usage.
[in,out] altDescr A pointer to a start of an array with prepared alternate descriptors. The last descriptor will have its cycle control type reprogrammed to a basic type.
[in] count A number of alternate descriptors in altDescr array. The maximum number of alternate descriptors is 256.

DMA_CfgChannel()

void DMA_CfgChannel ( unsigned int channel,
DMA_CfgChannel_TypeDef * cfg
)

Configure a DMA channel.

Configure miscellaneous issues for a DMA channel. This function is typically used once to set up a channel for a certain type of use.

Note
If using this function on a channel already in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to configure.
[in] cfg The configuration to use.

DMA_CfgDescr()

void DMA_CfgDescr ( unsigned int channel,
bool primary,
DMA_CfgDescr_TypeDef * cfg
)

Configure the DMA descriptor for auto-request, basic, or ping-pong DMA cycles.

This function is used to configure a descriptor for the following DMA cycle types:

  • auto-request - used for a memory/memory transfer
  • basic - used for a peripheral/memory transfer
  • ping-pong - used for a ping-pong-based peripheral/memory transfer style providing time to refresh one descriptor while the other is in use.

The DMA cycle is not activated. See DMA_ActivateAuto() , DMA_ActivateBasic() , or DMA_ActivatePingPong() to activate the DMA cycle. In many cases, the configuration only has to be done once, and all subsequent cycles may be activated with the activate function.

For ping-pong DMA cycles, this function must be used both on the primary and the alternate descriptor prior to activating the DMA cycle.

Notice that the DMA channel must also be configured. See DMA_CfgChannel() .

Note
If using this function on a descriptor already activated and in use by the DMA controller, the behavior is undefined.
Parameters
[in] channel The DMA channel to configure for.
[in] primary
  • true - configure the primary descriptor
  • false - configure an alternate descriptor
[in] cfg The configuration to use.

DMA_CfgDescrScatterGather()

void DMA_CfgDescrScatterGather ( DMA_DESCRIPTOR_TypeDef * descr,
unsigned int indx,
DMA_CfgDescrSGAlt_TypeDef * cfg
)

Configure an alternate DMA descriptor for use with scatter-gather DMA cycles.

In scatter-gather mode, the alternate descriptors are located in one contiguous memory area. Each of the alternate descriptors must be fully configured prior to starting the scatter-gather DMA cycle.

The DMA cycle is not activated by this function. See DMA_ActivateScatterGather() to activate the DMA cycle. In some cases, the alternate configuration only has to be done once and all subsequent transfers may be activated with the activate function.

Notice that the DMA channel must also be configured, see DMA_CfgChannel() .

Parameters
[in] descr Points to the start of a memory area holding the alternate descriptors.
[in] indx An alternate descriptor index number to configure (numbered from 0).
[in] cfg The configuration to use.

DMA_ChannelEnable()

void DMA_ChannelEnable ( unsigned int channel,
bool enable
)

Enable or disable a DMA channel.

Use this function to explicitly enable or disable a DMA channel. A DMA channel is automatically disabled when the DMA controller has finished a transaction.

Parameters
[in] channel The DMA channel to enable or disable.
[in] enable If 'true', the channel will be enabled. If 'false', the channel will be disabled.

DMA_ChannelEnabled()

bool DMA_ChannelEnabled ( unsigned int channel )

Check if the DMA channel is enabled.

The DMA channel is disabled when the DMA controller has finished a DMA cycle.

Parameters
[in] channel The DMA channel to check.
Returns
True if the channel is enabled, false if not.

DMA_ChannelRequestEnable()

void DMA_ChannelRequestEnable ( unsigned int channel,
bool enable
)

Enable or disable a DMA channel request.

Use this function to enable or disable a DMA channel request. This will prevent the DMA from proceeding after its current transaction if disabled.

Parameters
[in] channel The DMA channel to enable or disable the request on.
[in] enable If 'true', the request will be enabled. If 'false', the request will be disabled.

DMA_Init()

void DMA_Init ( DMA_Init_TypeDef * init )

Initialize the DMA controller.

This function resets and prepares the DMA controller for use. Although it may be used several times, it is normally only used during system initialization. If reused during a normal operation, any ongoing DMA transfers will be aborted. When complete, the DMA controller is in an enabled state.

Note
Must be invoked before using the DMA controller.
Parameters
[in] init A pointer to a structure containing the DMA initialization information.

DMA_IRQHandler()

void DMA_IRQHandler ( void )

Interrupt handler for the DMA cycle completion handling.

Clears any pending flags and calls registered callback (if any).

If using the default interrupt vector table setup provided, this function is automatically placed in the IRQ table due to weak linking. If taking control over the interrupt vector table in some other way, this interrupt handler must be installed to support callback actions.

For the user to implement a custom IRQ handler or run without a DMA IRQ handler, define EXCLUDE_DEFAULT_DMA_IRQ_HANDLER with a #define statement or with the compiler option -D.

DMA_RefreshPingPong()

void DMA_RefreshPingPong ( unsigned int channel,
bool primary,
bool useBurst,
void * dst,
const void * src,
unsigned int nMinus1,
bool stop
)

Refresh a descriptor used in a DMA ping-pong cycle.

During a ping-pong DMA cycle, the DMA controller automatically alternates between the primary and alternate descriptors, when completing use of a descriptor. While the other descriptor is in use by the DMA controller, the software should refresh the completed descriptor. This is typically done from the callback defined for the ping-pong cycle.

Parameters
[in] channel The DMA channel to refresh the ping-pong descriptor for.
[in] primary
  • true - refresh the primary descriptor
  • false - refresh an alternate descriptor
[in] useBurst The burst feature is only used on peripherals supporting DMA bursts. Bursts must not be used if the total length (as given by nMinus1) is less than the arbitration rate configured for the descriptor. See the reference manual for more details on burst usage.
[in] dst An address to a start location to transfer data to. If NULL, leave setting in descriptor as is.
[in] src An address to a start location to transfer data from. If NULL, leave setting in descriptor as is.
[in] nMinus1 A number of DMA transfer elements (minus 1) to transfer (<= 1023). The size of the DMA transfer element (1, 2 or 4 bytes) is configured with DMA_CfgDescr() .
[in] stop Indicate that the DMA ping-pong cycle stops when done using this descriptor.

DMA_Reset()

void DMA_Reset ( void )

Reset the DMA controller.

This functions will disable the DMA controller and set it to a reset state.

Note
Note that any ongoing transfers will be aborted.

DMA_IntClear()

void DMA_IntClear ( uint32_t flags )
inline

Clear one or more pending DMA interrupts.

Parameters
[in] flags Pending DMA interrupt sources to clear. Use one or more valid interrupt flags for the DMA module (DMA_IFC_nnn).

DMA_IntDisable()

void DMA_IntDisable ( uint32_t flags )
inline

Disable one or more DMA interrupts.

Parameters
[in] flags DMA interrupt sources to disable. Use one or more valid interrupt flags for the DMA module (DMA_IEN_nnn).

DMA_IntEnable()

void DMA_IntEnable ( uint32_t flags )
inline

Enable one or more DMA interrupts.

Note
Depending on the use, a pending interrupt may already be set prior to enabling the interrupt. To ignore a pending interrupt, consider using DMA_IntClear() prior to enabling the interrupt.
Parameters
[in] flags DMA interrupt sources to enable. Use one or more valid interrupt flags for the DMA module (DMA_IEN_nnn).

DMA_IntGet()

uint32_t DMA_IntGet ( void )
inline

Get pending DMA interrupt flags.

Note
Event bits are not cleared by the use of this function.
Returns
DMA interrupt sources pending. Returns one or more valid interrupt flags for the DMA module (DMA_IF_nnn).

DMA_IntGetEnabled()

uint32_t DMA_IntGetEnabled ( void )
inline

Get enabled and pending DMA interrupt flags.

Useful for handling more interrupt sources in the same interrupt handler.

Note
Interrupt flags are not cleared by the use of this function.
Returns
Pending and enabled DMA interrupt sources Return value is the bitwise AND of
  • the enabled interrupt sources in DMA_IEN and
  • the pending interrupt flags DMA_IF.

DMA_IntSet()

void DMA_IntSet ( uint32_t flags )
inline

Set one or more pending DMA interrupts.

Parameters
[in] flags DMA interrupt sources to set to pending. Use one or more valid interrupt flags for the DMA module (DMA_IFS_nnn).

Typedef Documentation

DMA_FuncPtr_TypeDef

typedef void(* DMA_FuncPtr_TypeDef) (unsigned int channel, bool primary, void *user)

DMA interrupt callback function pointer.

Parameters:

  • channel - DMA channel the callback function is invoked for.
  • primary - Indicates if callback is invoked for completion of primary (true) or alternate (false) descriptor. Mainly useful for ping-pong DMA cycles, to know which descriptor to refresh.
  • user - User definable reference that may be used to pass information to be used by the callback handler. If used, referenced data must be valid at the point when the interrupt handler invokes callback. If callback changes any data in the provided user structure, remember that those changes are done in interrupt context and proper protection of data may be required.

Enumeration Type Documentation

DMA_DataInc_TypeDef

Amount source/destination address should be incremented for each data transfer.

Enumerator
dmaDataInc1

Increment address 1 byte.

dmaDataInc2

Increment address 2 bytes.

dmaDataInc4

Increment address 4 bytes.

dmaDataIncNone

Do not increment address.

DMA_DataSize_TypeDef

Data sizes (in number of bytes) to be read/written by DMA transfer.

Enumerator
dmaDataSize1

1 byte DMA transfer size.

dmaDataSize2

2 byte DMA transfer size.

dmaDataSize4

4 byte DMA transfer size.

DMA_CycleCtrl_TypeDef

Types of DMA transfer.

Enumerator
dmaCycleCtrlBasic

Basic DMA cycle.

dmaCycleCtrlAuto

Auto-request DMA cycle.

dmaCycleCtrlPingPong

Ping-pong DMA cycle.

dmaCycleCtrlMemScatterGather

Memory scatter-gather DMA cycle.

dmaCycleCtrlPerScatterGather

Peripheral scatter-gather DMA cycle.

DMA_ArbiterConfig_TypeDef

Number of transfers before controller does new arbitration.

Enumerator
dmaArbitrate1

Arbitrate after 1 DMA transfer.

dmaArbitrate2

Arbitrate after 2 DMA transfers.

dmaArbitrate4

Arbitrate after 4 DMA transfers.

dmaArbitrate8

Arbitrate after 8 DMA transfers.

dmaArbitrate16

Arbitrate after 16 DMA transfers.

dmaArbitrate32

Arbitrate after 32 DMA transfers.

dmaArbitrate64

Arbitrate after 64 DMA transfers.

dmaArbitrate128

Arbitrate after 128 DMA transfers.

dmaArbitrate256

Arbitrate after 256 DMA transfers.

dmaArbitrate512

Arbitrate after 512 DMA transfers.

dmaArbitrate1024

Arbitrate after 1024 DMA transfers.