SAI Interface

Driver API for Serial Audio Interface (Driver_SAI.h) More...

Content
	Status Error Codes
	Negative values indicate errors (SAI has specific codes in addition to common Status Error Codes).
	SAI Events
	The SAI driver generates call back events that are notified via the function ARM_SAI_SignalEvent.
	SAI Control Codes
	Many parameters of the SAI driver are configured using the ARM_SAI_Control function.

Data Structures
struct	ARM_DRIVER_SAI
	Access structure of the SAI Driver. More...
struct	ARM_SAI_CAPABILITIES
	SAI Driver Capabilities. More...
struct	ARM_SAI_STATUS
	SAI Status. More...

Typedefs
typedef void(*	ARM_SAI_SignalEvent_t )(uint32_t event)
	Pointer to ARM_SAI_SignalEvent : Signal SAI Event.

Functions
ARM_DRIVER_VERSION	ARM_SAI_GetVersion (void)
	Get driver version.
ARM_SAI_CAPABILITIES	ARM_SAI_GetCapabilities (void)
	Get driver capabilities.
int32_t	ARM_SAI_Initialize (ARM_SAI_SignalEvent_t cb_event)
	Initialize SAI Interface.
int32_t	ARM_SAI_Uninitialize (void)
	De-initialize SAI Interface.
int32_t	ARM_SAI_PowerControl (ARM_POWER_STATE state)
	Control SAI Interface Power.
int32_t	ARM_SAI_Send (const void *data, uint32_t num)
	Start sending data to SAI transmitter.
int32_t	ARM_SAI_Receive (void *data, uint32_t num)
	Start receiving data from SAI receiver.
uint32_t	ARM_SAI_GetTxCount (void)
	Get transmitted data count.
uint32_t	ARM_SAI_GetRxCount (void)
	Get received data count.
int32_t	ARM_SAI_Control (uint32_t control, uint32_t arg1, uint32_t arg2)
	Control SAI Interface.
ARM_SAI_STATUS	ARM_SAI_GetStatus (void)
	Get SAI status.
void	ARM_SAI_SignalEvent (uint32_t event)
	Signal SAI Events.

Description

Driver API for Serial Audio Interface (Driver_SAI.h)

The Serial Audio Interface (SAI) implements a synchronous serial bus interface for connecting digital audio devices. It is by far the most common mechanism used to transfer two channels of audio data between devices within a system. SAI can transfer digital audio using various protocols:

• I2S
• MSB Justified
• LSB Justified
• PCM
• AC'97
• User Defined Protocol

Block Diagram

 

Simplified SAI Schematic

 

SAI API

The following header files define the Application Programming Interface (API) for the SAI interface:

• Driver_SAI.h : Driver API for Serial Audio Interface

The driver implementation is a typical part of the Device Family Pack (DFP) that supports the peripherals of the microcontroller family.

Driver Functions

The driver functions are published in the access struct as explained in Common Driver Functions

• ARM_DRIVER_SAI : access struct for SAI driver functions

I2S

Integrated Interchip Sound (I2S) is a serial bus interface that connects digital audio devices together. It was introduced by Philips (now NXP) in the late 80's and last revised 1996. It uses pulse code modulation to exchange the audio data between the devices. The following timing diagram explains the operation:

I2S separates the clock (SCK) from the serial data (SD), resulting in a lower jitter. A complete audio data frame consists of two slots, one for the left channel and one for the right. The slot size equals the data size. The word select (WS) line lets the device know whether the left channel (WS is low) or the right channel (WS is high) is currently being transmitted. WS has a 50% duty-cycle signal that has the same frequency as the sample frequency. It is an early signal, meaning that the WS line changes one clock cycle before the actual data (SD) is transmitted (left or right). The data on SD is always transmitted MSB first and can have a data size of 8 up to 32 bits.

In terms of the CMSIS-Driver for SAI, the I2S protocol can be described as follows:

• Data Size: 8..32 (MSB first)
• Clock Polarity: Drive on falling edge, Capture on rising edge
• Frame Length: 2 * Data Size = 2 * Slot Size
• Frame Sync Width: Frame Length / 2
• Frame Sync Polarity: Active Low
• Frame Sync Early
• Slot Count: 2 (L R)
• Slot Size: Data Size
• Slot Offset: 0

MSB Justified

MSB Justified is much like I2S, with a few differences:

Unlike I2S, in MSB Justified the word select (WS) signals the left channel when it is active high and the right channel, when it is active low. The signal changes when the first actual SD data is available. It might happen that a frame (left or right) is not fully filled with data. In this case, all data after the LSB is forced to zero.

In terms of the CMSIS-Driver for SAI, the MSB Justified protocol can be described as follows:

• Data Size: 8..32 (MSB first)
• Clock Polarity: Drive on falling edge, Capture on rising edge
• Frame Length: 2 * Slot Size
• Frame Sync Width: Frame Length / 2
• Frame Sync Polarity: Active High
• Slot Count: 2 (L R)
• Slot Size: Data Size or higher (16/32)
• Slot Offset: 0 (Zero padding after Data: Slot Size - Data Size)

LSB Justified

LSB Justified is much like MSB Justified, with the single difference that the padding 0's are sent before the first actual data (MSB on SD):

In terms of the CMSIS-Driver for SAI, the LSB Justified protocol can be described as follows:

• Data Size: 8..32 (MSB first)
• Clock Polarity: Drive on falling edge, Capture on rising edge
• Frame Length: 2*Slot Size
• Frame Sync Width: Frame Length / 2
• Frame Sync Polarity: Active High
• Slot Count: 2
• Slot Size: Data Size or higher (16/32)
• Slot Offset: Slot Size - Data Size (Zero padding before Data: Slot Size - Data Size)

PCM

Pulse Code Modulation (PCM) differs to the previous protocols in a few ways:

• Only one channel is transferred.

• There are two types of synchronization modes available:
  • In short frame sync mode, the falling edge of Frame Sync indicates the start of the serial data SD. Frame Sync is always one clock cycle long.
  • In long frame sync mode, the rising edge of Frame Sync indicates the start of the serial data SD. Frame Sync stays active high for 13 clock cycles.

In terms of the CMSIS-Driver for SAI, the PCM protocol can be described as follows:
PCM Short Frame

• Data Size: 8..32 (MSB first)
• Clock Polarity: Drive on falling edge, Capture on rising edge
• Frame Length: Slot Size
• Frame Sync Width: 1
• Frame Sync Polarity: Active High
• Frame Sync Early
• Slot Count: 1
• Slot Size: Data Size or higher (16/32)
• Slot Offset: 0

PCM Long Frame

• Data Size: 16..32 (MSB first)
• Clock Polarity: Drive on falling edge, Capture on rising edge
• Frame Length: Slot Size
• Frame Sync Width: 13
• Frame Sync Polarity: Active High
• Slot Count: 1
• Slot Size: Data Size or higher (32)
• Slot Offset: 0

AC'97

Audio Codec '97 was developed by Intel. It is composed of five wires: the clock (12.288 MHz), a sync signal, a reset signal, and two data wires: sdata_out (contains the AC97 output) and sdata_in (contains the CODEC output). For more information, consult the standard documentation.

User Defined Protocol

Using the control structs of the CMSIS-Driver SAI, it is possible to create support for nearly all serial audio protocols that are available today.

The following properties can be configured for a user protocol:

• Data Size in bits (8..32)
• Data Bit Order: MSB first (default) or LSB first
• Clock Polarity:
  • Driver on falling edge, Capture on rising edge (default)
  • Driver on rising edge, Capture on falling edge
• Frame Length in bits
• Frame Sync Width in bits (default=1)
• Frame Sync Polarity: active high (default) or low
• Frame Sync Early: Sync signal one bit before the first bit of frame
• Slot Count: number of slots in frame (default=1)
• Slot Size: equal to data size (default) or 16 or 32-bit
• Slot Offset: offset of first data bit in slot (default=0)

For more information, refer to ARM_SAI_Control that explains the different configuration options in more detail.

---

Data Structure Documentation

struct ARM_DRIVER_SAI

Access structure of the SAI Driver.

The functions of the SAI driver are accessed by function pointers exposed by this structure. Refer to Common Driver Functions for overview information.

Each instance of an SAI interface provides such an access structure. The instance is identified by a postfix number in the symbol name of the access structure, for example:

• Driver_SAI0 is the name of the access struct of the first instance (no. 0).
• Driver_SAI1 is the name of the access struct of the second instance (no. 1).

A middleware configuration setting allows connecting the middleware to a specific driver instance Driver_SAIn. The default is 0, which connects a middleware to the first instance of a driver.

Data Fields
ARM_DRIVER_VERSION(*	GetVersion )(void)
	Pointer to ARM_SAI_GetVersion : Get driver version.
ARM_SAI_CAPABILITIES(*	GetCapabilities )(void)
	Pointer to ARM_SAI_GetCapabilities : Get driver capabilities.
int32_t(*	Initialize )(ARM_SAI_SignalEvent_t cb_event)
	Pointer to ARM_SAI_Initialize : Initialize SAI Interface.
int32_t(*	Uninitialize )(void)
	Pointer to ARM_SAI_Uninitialize : De-initialize SAI Interface.
int32_t(*	PowerControl )(ARM_POWER_STATE state)
	Pointer to ARM_SAI_PowerControl : Control SAI Interface Power.
int32_t(*	Send )(const void *data, uint32_t num)
	Pointer to ARM_SAI_Send : Start sending data to SAI Interface.
int32_t(*	Receive )(void *data, uint32_t num)
	Pointer to ARM_SAI_Receive : Start receiving data from SAI Interface.
uint32_t(*	GetTxCount )(void)
	Pointer to ARM_SAI_GetTxCount : Get transmitted data count.
uint32_t(*	GetRxCount )(void)
	Pointer to ARM_SAI_GetRxCount : Get received data count.
int32_t(*	Control )(uint32_t control, uint32_t arg1, uint32_t arg2)
	Pointer to ARM_SAI_Control : Control SAI Interface.
ARM_SAI_STATUS(*	GetStatus )(void)
	Pointer to ARM_SAI_GetStatus : Get SAI status.

Field Documentation

ARM_DRIVER_VERSION(* GetVersion)(void)

Pointer to ARM_SAI_GetVersion : Get driver version.

ARM_SAI_CAPABILITIES(* GetCapabilities)(void)

Pointer to ARM_SAI_GetCapabilities : Get driver capabilities.

int32_t(* Initialize)(ARM_SAI_SignalEvent_t cb_event)

Pointer to ARM_SAI_Initialize : Initialize SAI Interface.

int32_t(* Uninitialize)(void)

Pointer to ARM_SAI_Uninitialize : De-initialize SAI Interface.

int32_t(* PowerControl)(ARM_POWER_STATE state)

Pointer to ARM_SAI_PowerControl : Control SAI Interface Power.

int32_t(* Send)(const void *data, uint32_t num)

Pointer to ARM_SAI_Send : Start sending data to SAI Interface.

int32_t(* Receive)(void *data, uint32_t num)

Pointer to ARM_SAI_Receive : Start receiving data from SAI Interface.

uint32_t(* GetTxCount)(void)

Pointer to ARM_SAI_GetTxCount : Get transmitted data count.

uint32_t(* GetRxCount)(void)

Pointer to ARM_SAI_GetRxCount : Get received data count.

int32_t(* Control)(uint32_t control, uint32_t arg1, uint32_t arg2)

Pointer to ARM_SAI_Control : Control SAI Interface.

ARM_SAI_STATUS(* GetStatus)(void)

Pointer to ARM_SAI_GetStatus : Get SAI status.

struct ARM_SAI_CAPABILITIES

SAI Driver Capabilities.

An SAI driver can be implemented with different capabilities (for example protocol support). The data fields of this structure encode the capabilities implemented by this driver. If a certain hardware peripheral is not able to handle one of the protocols directly (not advertised using ARM_SAI_CAPABILITIES), then it might be possible to implement it using the User Defined Protocol (if supported).

Returned by:

• ARM_SAI_GetCapabilities

Data Fields
uint32_t	asynchronous: 1	supports asynchronous Transmit/Receive
uint32_t	synchronous: 1	supports synchronous Transmit/Receive
uint32_t	protocol_user: 1	supports user defined Protocol
uint32_t	protocol_i2s: 1	supports I2S Protocol
uint32_t	protocol_justified: 1	supports MSB/LSB justified Protocol
uint32_t	protocol_pcm: 1	supports PCM short/long frame Protocol
uint32_t	protocol_ac97: 1	supports AC'97 Protocol
uint32_t	mono_mode: 1	supports Mono mode
uint32_t	companding: 1	supports Companding
uint32_t	mclk_pin: 1	supports MCLK (Master Clock) pin
uint32_t	event_frame_error: 1	supports Frame error event: ARM_SAI_EVENT_FRAME_ERROR

struct ARM_SAI_STATUS

SAI Status.

Structure with information about the status of the SAI. The data fields encode busy flags and error flags.

Returned by:

• ARM_SAI_GetStatus

Data Fields
uint32_t	tx_busy: 1	Transmitter busy flag.
uint32_t	rx_busy: 1	Receiver busy flag.
uint32_t	tx_underflow: 1	Transmit data underflow detected (cleared on start of next send operation)
uint32_t	rx_overflow: 1	Receive data overflow detected (cleared on start of next receive operation)
uint32_t	frame_error: 1	Sync Frame error detected (cleared on start of next send/receive operation)

Typedef Documentation

ARM_SAI_SignalEvent_t

Pointer to ARM_SAI_SignalEvent : Signal SAI Event.

Provides the typedef for the callback function ARM_SAI_SignalEvent.

Parameter for:

• ARM_SAI_Initialize

Function Documentation

ARM_DRIVER_VERSION ARM_SAI_GetVersion

(

void

)

Get driver version.

Returns

ARM_DRIVER_VERSION

The function ARM_SAI_GetVersion returns version information of the driver implementation in ARM_DRIVER_VERSION

• API version is the version of the CMSIS-Driver specification used to implement this driver.
• Driver version is source code version of the actual driver implementation.

Example:

extern ARM_DRIVER_SAI Driver_SAI0;
ARM_DRIVER_SAI *drv_info;
 
void setup_sai (void)  {
  ARM_DRIVER_VERSION  version;
 
  drv_info = &Driver_SAI0;  
  version = drv_info->GetVersion ();
  if (version.api < 0x10A)  {      // requires at minimum API version 1.10 or higher
    // error handling
    return;
  }
}

ARM_SAI_CAPABILITIES ARM_SAI_GetCapabilities

(

void

)

Get driver capabilities.

Returns

ARM_SAI_CAPABILITIES

The function ARM_SAI_GetCapabilities retrieves information about the capabilities in this driver implementation. The data fields of the struct ARM_SAI_CAPABILITIES encode various capabilities, for example supported protocols, or if a hardware is capable to create signal events using the ARM_SAI_SignalEvent callback function.

Example:

extern ARM_DRIVER_SAI Driver_SAI0;
ARM_DRIVER_SAI *drv_info;
  
void read_capabilities (void)  {
  ARM_SAI_CAPABILITIES drv_capabilities;
 
  drv_info = &Driver_SAI0;  
  drv_capabilities = drv_info->GetCapabilities ();
  // interrogate capabilities
 
}

int32_t ARM_SAI_Initialize

(

ARM_SAI_SignalEvent_t

cb_event

)

Initialize SAI Interface.

Parameters

[in]

cb_event

Pointer to ARM_SAI_SignalEvent

Returns

Status Error Codes

The function ARM_SAI_Initialize initializes the SAI interface. It is called when the middleware component starts operation.

The function performs the following operations:

• Initializes the required resources of the SAI interface.
• Registers the ARM_SAI_SignalEvent callback function.

The parameter cb_event is a pointer to the ARM_SAI_SignalEvent callback function; use a NULL pointer when no callback signals are required.

int32_t ARM_SAI_Uninitialize

(

void

)

De-initialize SAI Interface.

Returns

Status Error Codes

The function ARM_SAI_Uninitialize de-initializes the resources of SAI interface.

It is called when the middleware component stops operation and releases the software resources used by the interface.

int32_t ARM_SAI_PowerControl

(

ARM_POWER_STATE

state

)

Control SAI Interface Power.

Parameters

[in]

state

Power state

Returns

Status Error Codes

The function ARM_SAI_PowerControl allows you to control the power modes of the SAI interface.

The parameter state sets the operation and can have the following values:

• ARM_POWER_FULL : set-up peripheral for data transfers, enable interrupts (NVIC) and optionally DMA. Can be called multiple times. If the peripheral is already in this mode the function performs no operation and returns with ARM_DRIVER_OK.
• ARM_POWER_LOW : may use power saving. Returns ARM_DRIVER_ERROR_UNSUPPORTED when not implemented.
• ARM_POWER_OFF : terminates any pending data transfers, disables peripheral, disables related interrupts and DMA.

Refer to Function Call Sequence for more information.

int32_t ARM_SAI_Send	(	const void *	data,
		uint32_t	num
	)

Start sending data to SAI transmitter.

Parameters

[in]	data	Pointer to buffer with data to send to SAI transmitter
[in]	num	Number of data items to send

Returns

Status Error Codes

The function ARM_SAI_Send sends data to the SAI transmitter.

The function parameters specify the buffer with data and the number num of items to send. The item size is defined by the data type which depends on the configured number of data bits.

Data type is:

• uint8_t when configured for 8 data bits
• uint16_t when configured for 9..16 data bits
• uint32_t when configured for 17..32 data bits

Transmitter is enabled by calling ARM_SAI_Control with ARM_SAI_CONTROL_TX as the control parameter and 1 as an argument. This starts the transmit engine which, generates a clock and frame sync signal in master mode and transmits the data. In slave mode, clock and frame sync are generated by the external master. When mute is active, data is discarded and zero values are transmitted.

Calling the function ARM_SAI_Send only starts the send operation. The function is non-blocking and returns as soon as the driver has started the operation (the driver typically configures DMA or the interrupt system for continuous transfer). During the operation it is not allowed to call this function again. Also, the data buffer must stay allocated and the contents of unsent data must not be modified. When the send operation is completed (requested number of items have been sent), the event ARM_SAI_EVENT_SEND_COMPLETE is generated. Progress of the send operation can be monitored by reading the number of already sent items by calling the function ARM_SAI_GetTxCount.

The status of the transmitter can also be monitored by calling the function ARM_SAI_GetStatus and checking the tx_busy flag, which indicates if a transmission is still in progress.

If the transmitter is enabled and data is to be sent but the send operation has not been started yet, then the event ARM_SAI_EVENT_TX_UNDERFLOW is generated.

If an invalid synchronization frame is detected in slave mode, then the event ARM_SAI_EVENT_FRAME_ERROR is generated (if supported and reported by event_frame_error in ARM_SAI_CAPABILITIES).

The send operation can be aborted by calling the function ARM_SAI_Control with the control parameter ARM_SAI_ABORT_SEND.

int32_t ARM_SAI_Receive	(	void *	data,
		uint32_t	num
	)

Start receiving data from SAI receiver.

Parameters

[out]	data	Pointer to buffer for data to receive from SAI receiver
[in]	num	Number of data items to receive

Returns

Status Error Codes

The function ARM_SAI_Receive is used to receive data from the SAI receiver. The function parameters specify the buffer for data and the number num of items to receive. The item size is defined by the data type, which depends on the configured number of data bits.

Data type is:

• uint8_t when configured for 8 data bits
• uint16_t when configured for 9..16 data bits
• uint32_t when configured for 17..32 data bits

The receiver is enabled by calling the function ARM_SAI_Control with the control parameter ARM_SAI_CONTROL_RX and the value 1 for the parameter arg1. This starts the receive engine, which generates a clock and frame sync signal in master mode and receives data. In slave mode, clock and frame sync are generated by the external master.

Calling the function ARM_SAI_Receive only starts the receive operation. The function is non-blocking and returns as soon as the driver has started the operation (the driver typically configures DMA or the interrupt system for continuous transfer). During the operation, it is not allowed to call this function again. The data buffer must also stay allocated. When receive operation is completed (the requested number of items have been received), the ARM_SAI_EVENT_RECEIVE_COMPLETE event is generated. Progress of the receive operation can also be monitored by reading the number of items already received by calling the function ARM_SAI_GetRxCount.

The status of the receiver can also be monitored by calling the function ARM_SAI_GetStatus and checking the rx_busy flag, which indicates whether a reception is still in progress.

When the receiver is enabled and data is received but the receive operation has not been started yet, then the event ARM_SAI_EVENT_RX_OVERFLOW is generated.

If an invalid synchronization frame is detected in slave mode, then the event ARM_SAI_EVENT_FRAME_ERROR is generated (if supported and reported by event_frame_error in ARM_SAI_CAPABILITIES).

The receive operation can be aborted by calling the function ARM_SAI_Control with the control parameter ARM_SAI_ABORT_RECEIVE.

uint32_t ARM_SAI_GetTxCount

(

void

)

Get transmitted data count.

Returns

number of data items transmitted

The function ARM_SAI_GetTxCount returns the number of the currently transmitted data items during an ARM_SAI_Send operation.

uint32_t ARM_SAI_GetRxCount

(

void

)

Get received data count.

Returns

number of data items received

The function ARM_SAI_GetRxCount returns the number of the currently received data items during an ARM_SAI_Receive operation.

int32_t ARM_SAI_Control	(	uint32_t	control,
		uint32_t	arg1,
		uint32_t	arg2
	)

Control SAI Interface.

Parameters

[in]	control	Operation
[in]	arg1	Argument 1 of operation (optional)
[in]	arg2	Argument 2 of operation (optional)

Returns

common Status Error Codes and driver specific Status Error Codes

The function ARM_SAI_Control controls the SAI interface and executes various operations.

The parameter control specifies the operation. Values are listed in the table Parameter control.
The parameter arg1 provides, depending on the operation, additional information or sets values. Refer to table Parameter arg1.
The parameter arg2 provides, depending on the operation and/or arg1, additional information or sets values.

The driver provides a receiver/transmitter pair of signals. In asynchronous operation mode, they operate completely independent from each other. In synchronous operation mode, the synchronous channel uses the Clock (SCK) and Frame Sync (WS) signal from the asynchronous one (control category Synchronization).

The clock polarity can be set for every protocol, regardless whether it is already predefined for I2S, MSB/LSB Jusitified (control category Clock Polarity).

A master clock provides a faster clock from which the frame can be derived (usually 256 x faster than the normal frame clock). You can use a master clock only in master mode. A slave will always have only one clock (control category Master Clock pin (MCLK)).

The table lists the operation values for control. Values from different categories can be ORed.

Parameter control	Bit	Category	Description
ARM_SAI_CONFIGURE_TX	0..7	Operation	Configure transmitter. arg1 (see Parameter arg1) and arg2 provide additional configuration.
ARM_SAI_CONFIGURE_TX			Configure transmitter. arg1 (see Parameter arg1) and arg2 provide additional configuration.
ARM_SAI_CONFIGURE_RX			Configure transmitter. arg1 and arg2 provide additional configuration.
ARM_SAI_CONTROL_TX			Enable or disable transmitter and control mute; arg1.0 : 0=disable (default); 1=enable; arg1.1 : mute (see ARM_SAI_Send)
ARM_SAI_CONTROL_RX			Enable or disable receiver; arg1.0 : 0=disable (default); 1=enable (see ARM_SAI_Receive)
ARM_SAI_MASK_SLOTS_TX			Mask transmitter slots; arg1 = mask (bit: 0=active, 1=inactive); all configured slots are active by default.
ARM_SAI_MASK_SLOTS_RX			Mask receiver slots; arg1 = mask (bit: 0=active, 1=inactive); all configured slots are active by default.
ARM_SAI_ABORT_SEND			Abort send operation (see ARM_SAI_Send).
ARM_SAI_ABORT_RECEIVE			Abort receive operation (see ARM_SAI_Receive).
ARM_SAI_MODE_MASTER	8	Mode	Master mode. arg2 specifies the audio frequency in [Hz]. You can also set the Master Clock pin.
ARM_SAI_MODE_SLAVE (default)			Slave mode.
ARM_SAI_ASYNCHRONOUS (default)	9	Synchronization	Asynchronous operation using own clock and sync signal.
ARM_SAI_SYNCHRONOUS			Synchronous operation using clock and sync signal from other transmitter/receiver.
ARM_SAI_PROTOCOL_USER (default)	10..12	Protocol	User defined
ARM_SAI_PROTOCOL_I2S			I2C
ARM_SAI_PROTOCOL_MSB_JUSTIFIED			MSB (left) justified
ARM_SAI_PROTOCOL_LSB_JUSTIFIED			LSB (right) justified
ARM_SAI_PROTOCOL_PCM_SHORT			PCM with short frame
ARM_SAI_PROTOCOL_PCM_LONG			PCM with long frame
ARM_SAI_PROTOCOL_AC97			AC'97
ARM_SAI_DATA_SIZE(n)	13..17	Data Size	Data size in bits; the range for n is 8..32. See also: Frame Slot Size.
ARM_SAI_MSB_FIRST	18	Bit Order	Data is transferred with MSB first.
ARM_SAI_LSB_FIRST			Data is transferred with LSB first (User protocol only, ignored otherwise).
ARM_SAI_MONO_MODE	19	Mono Mode	Only for I2S, MSB/LSB justified. When using I2S in mono mode, only data for a single channel is sent to and received from the driver. Hardware will duplicate the data for the second channel on transmit and ignore the second channel on receive.
ARM_SAI_COMPANDING_NONE (default)	20..22	Companding	No companding
ARM_SAI_COMPANDING_A_LAW			A-Law companding (8-bit data)
ARM_SAI_COMPANDING_U_LAW			u-Law companding (8-bit data)
ARM_SAI_CLOCK_POLARITY_0 (default) >	23	Clock Polarity	Drive on falling edge, capture on rising edge.
ARM_SAI_CLOCK_POLARITY_1			Drive on rising edge, capture on falling edge.
ARM_SAI_MCLK_PIN_INACTIVE (default)	24..26	Master Clock pin (MCLK)	MCLK not used.
ARM_SAI_MCLK_PIN_OUTPUT			MCLK is output (Master mode only).
ARM_SAI_MCLK_PIN_INPUT			MCLK is input (Master mode only).

The parameter arg1 provides frame-specific values depending on the control operation. Values from different categories can be ORed.

Parameter arg1	Bit	Category	Description
ARM_SAI_FRAME_LENGTH(n)	0..9	Frame Length	Frame length in bits; the possible range for n is 8..1024; default depends on protocol and data.
ARM_SAI_FRAME_SYNC_WIDTH(n)	10..17	Frame Sync Width	Frame Sync width in bits; the possible range for n is 1..256; default=1; User protocol only, ignored otherwise.
ARM_SAI_FRAME_SYNC_POLARITY_HIGH	18	Frame Sync Polarity	Frame Sync is active high (default).
ARM_SAI_FRAME_SYNC_POLARITY_LOW			Frame Sync is active low (User protocol only, ignored otherwise).
ARM_SAI_FRAME_SYNC_EARLY	19	Frame Sync Early	Frame Sync one bit before the first bit of the frame (User protocol only, ignored otherwise).
ARM_SAI_SLOT_COUNT(n)	20..24	Frame Sync Count	Number of slots in frame; the possible range for n is 1..32; default=1; User protocol only, ignored otherwise.
ARM_SAI_SLOT_SIZE_DEFAULT	25..26	Frame Slot Size	Slot size is equal to data size (default).
ARM_SAI_SLOT_SIZE_16			Slot size is 16 bits (User protocol only, ignored otherwise).
ARM_SAI_SLOT_SIZE_32			Slot size is 32 bits (User protocol only, ignored otherwise).
ARM_SAI_SLOT_OFFSET(n)	27..31	Frame Slot Offset	Offset of first data bit in slot; The range for n is 0..31; default=0; User protocol only, ignored otherwise.

Depending on the control operation, the parameter arg2 specifies the Master Clock (MCLK) prescaler and calculates the audio frequency automatically.

Parameter arg2	MCLK Prescaler
ARM_SAI_MCLK_PRESCALER(n)	MCLK prescaler; Audio frequency = MCLK/n; the range for n is 1..4096; default=1.

Example

extern ARM_DRIVER_SAI Driver_SAI0;
 
// configure Transmitter to Asynchronous Master: I2S Protocol, 16-bit data, 16kHz Audio frequency
status = Driver_SAI0.Control(ARM_SAI_CONFIGURE_TX | 
                             ARM_SAI_MODE_MASTER  | 
                             ARM_SAI_ASYNCHRONOUS | 
                             ARM_SAI_PROTOCOL_I2S | 
                             ARM_SAI_DATA_SIZE(16), 0, 16000);
 
// configure Receiver to Asynchronous Master: I2S Protocol, 16-bit data, 16kHz Audio frequency
status = Driver_SAI0.Control(ARM_SAI_CONFIGURE_RX | 
                             ARM_SAI_MODE_MASTER  | 
                             ARM_SAI_ASYNCHRONOUS | 
                             ARM_SAI_PROTOCOL_I2S | 
                             ARM_SAI_DATA_SIZE(16), 0, 16000);
 
// enable Transmitter
status = Driver_SAI0.Control(ARM_SAI_CONTROL_TX, 1, 0);
 
// enable Receiver
status = Driver_SAI0.Control(ARM_SAI_CONTROL_RX, 1, 0);

ARM_SAI_STATUS ARM_SAI_GetStatus

(

void

)

Get SAI status.

Returns

SAI status ARM_SAI_STATUS

The function ARM_SAI_GetStatus retrieves the current SAI interface status.

void ARM_SAI_SignalEvent

(

uint32_t

event

)

Signal SAI Events.

Parameters

[in]

event

SAI Events notification mask

Returns

none

The function ARM_SAI_SignalEvent is a callback function registered by the function ARM_SAI_Initialize.

The parameter event indicates one or more events that occurred during driver operation. Each event is encoded in a separate bit and therefore it is possible to signal multiple events within the same call.

The following events can be generated:

Parameter event	Bit	Description
ARM_SAI_EVENT_SEND_COMPLETE	0	Occurs after call to ARM_SAI_Send to indicate that all the data has been sent (or queued in transmit buffers). The driver is ready for the next call to ARM_SAI_Send.
ARM_SAI_EVENT_RECEIVE_COMPLETE	1	Occurs after call to ARM_SAI_Receive to indicate that all the data has been received. The driver is ready for the next call to ARM_SAI_Receive.
ARM_SAI_EVENT_TX_UNDERFLOW	2	Occurs when data is to be sent but send operation has not been started. Data field tx_underflow = 1 of ARM_SAI_STATUS.
ARM_SAI_EVENT_RX_OVERFLOW	3	Occurs when data is received but receive operation has not been started. Data field rx_underflow = 1 of ARM_SAI_STATUS.
ARM_SAI_EVENT_FRAME_ERROR	4	Occurs in slave mode when invalid synchronization frame is detected. Data field event_frame_error = 1 of ARM_SAI_STATUS.