SPI

Modules
	SPI_Registers

Data Structures
struct	mxc_spi_req_t

Typedefs
typedef void(*	spi_complete_cb_t) (void *req, int result)

Enumerations
enum	mxc_spi_width_t
enum	mxc_spi_mode_t

Functions
int	MXC_SPI_Init (mxc_spi_regs_t *spi, int masterMode, int quadModeUsed, int numSlaves, unsigned ssPolarity, unsigned int hz)
int	MXC_SPI_Shutdown (mxc_spi_regs_t *spi)
int	MXC_SPI_ReadyForSleep (mxc_spi_regs_t *spi)
int	MXC_SPI_GetPeripheralClock (mxc_spi_regs_t *spi)
int	MXC_SPI_SetFrequency (mxc_spi_regs_t *spi, unsigned int hz)
unsigned int	MXC_SPI_GetFrequency (mxc_spi_regs_t *spi)
int	MXC_SPI_SetDataSize (mxc_spi_regs_t *spi, int dataSize)
int	MXC_SPI_GetDataSize (mxc_spi_regs_t *spi)
int	MXC_SPI_SetSlave (mxc_spi_regs_t *spi, int ssIdx)
int	MXC_SPI_GetSlave (mxc_spi_regs_t *spi)
int	MXC_SPI_SetWidth (mxc_spi_regs_t *spi, mxc_spi_width_t spiWidth)
mxc_spi_width_t	MXC_SPI_GetWidth (mxc_spi_regs_t *spi)
int	MXC_SPI_SetMode (mxc_spi_regs_t *spi, mxc_spi_mode_t spiMode)
mxc_spi_mode_t	MXC_SPI_GetMode (mxc_spi_regs_t *spi)
int	MXC_SPI_StartTransmission (mxc_spi_regs_t *spi)
int	MXC_SPI_GetActive (mxc_spi_regs_t *spi)
int	MXC_SPI_AbortTransmission (mxc_spi_regs_t *spi)
unsigned int	MXC_SPI_ReadRXFIFO (mxc_spi_regs_t *spi, unsigned char *bytes, unsigned int len)
unsigned int	MXC_SPI_GetRXFIFOAvailable (mxc_spi_regs_t *spi)
unsigned int	MXC_SPI_WriteTXFIFO (mxc_spi_regs_t *spi, unsigned char *bytes, unsigned int len)
unsigned int	MXC_SPI_GetTXFIFOAvailable (mxc_spi_regs_t *spi)
void	MXC_SPI_ClearRXFIFO (mxc_spi_regs_t *spi)
void	MXC_SPI_ClearTXFIFO (mxc_spi_regs_t *spi)
int	MXC_SPI_SetRXThreshold (mxc_spi_regs_t *spi, unsigned int numBytes)
unsigned int	MXC_SPI_GetRXThreshold (mxc_spi_regs_t *spi)
int	MXC_SPI_SetTXThreshold (mxc_spi_regs_t *spi, unsigned int numBytes)
unsigned int	MXC_SPI_GetTXThreshold (mxc_spi_regs_t *spi)
unsigned int	MXC_SPI_GetFlags (mxc_spi_regs_t *spi)
void	MXC_SPI_ClearFlags (mxc_spi_regs_t *spi)
void	MXC_SPI_EnableInt (mxc_spi_regs_t *spi, unsigned int mask)
void	MXC_SPI_DisableInt (mxc_spi_regs_t *spi, unsigned int mask)
int	MXC_SPI_MasterTransaction (mxc_spi_req_t *req)
int	MXC_SPI_MasterTransactionAsync (mxc_spi_req_t *req)
int	MXC_SPI_MasterTransactionDMA (mxc_spi_req_t *req)
int	MXC_SPI_SlaveTransaction (mxc_spi_req_t *req)
int	MXC_SPI_SlaveTransactionAsync (mxc_spi_req_t *req)
int	MXC_SPI_SlaveTransactionDMA (mxc_spi_req_t *req)
int	MXC_SPI_SetDefaultTXData (mxc_spi_regs_t *spi, unsigned int defaultTXData)
void	MXC_SPI_AbortAsync (mxc_spi_regs_t *spi)
void	MXC_SPI_AsyncHandler (mxc_spi_regs_t *spi)
void	MXC_SPI_HWSSControl (mxc_spi_regs_t *spi, int state)

Detailed Description

---

Data Structure Documentation

_mxc_spi_req_t

struct _mxc_spi_req_t

The information required to perform a complete SPI transaction.

This structure is used by blocking, async, and DMA based transactions.

Note

"completeCB" only needs to be initialized for interrupt driven (Async) and DMA transactions.

Data Fields
mxc_spi_regs_t *	spi
int	ssIdx
int	ssDeassert
uint8_t *	txData
uint8_t *	rxData
uint32_t	txLen
uint32_t	rxLen
uint32_t	txCnt
uint32_t	rxCnt
spi_complete_cb_t	completeCB

Field Documentation

rxData

uint8_t* rxData

Buffer to store received data For character sizes < 8 bits, pad the MSB of each byte with zeros. For character sizes > 8 bits, use two bytes per character and pad the MSB of the upper byte with zeros

txData

uint8_t* txData

Buffer containing transmit data. For character sizes < 8 bits, pad the MSB of each byte with zeros. For character sizes > 8 bits, use two bytes per character and pad the MSB of the upper byte with zeros

Typedef Documentation

spi_complete_cb_t

typedef void(* spi_complete_cb_t) (void *req, int result)

The callback routine used to indicate the transaction has terminated.

Parameters

req	The details of the transaction.
result	See Error Codes for the list of error codes.

Enumeration Type Documentation

mxc_spi_mode_t

enum mxc_spi_mode_t

The list of SPI modes.

SPI supports four combinations of clock and phase polarity

Clock polarity is controlled using the bit SPIn_CTRL2.cpol and determines if the clock is active high or active low

Clock phase determines when the data must be stable for sampling

Enumerator
SPI_MODE_0	clock phase = 0, clock polarity = 0
SPI_MODE_1	clock phase = 0, clock polarity = 1
SPI_MODE_2	clock phase = 1, clock polarity = 0
SPI_MODE_3	clock phase = 1, clock polarity = 1

mxc_spi_width_t

enum mxc_spi_width_t

The list of SPI Widths supported.

The SPI Width can be set on a per-transaction basis. An example use case of SPI_WIDTH_STANDARD_HALFDUPLEX is given.

Using a MAX31865 RTD-to-SPI IC, read back the temperature The IC requires a SPI Read to be executed as

1. Assert SS
2. Write an 8bit register address
3. Read back the 8 bit register
4. Deassert SS This can be accomplished with the STANDARD_HALFDUPLEX width

1. set txData to the address, txLen=1
2. set rxData to a buffer of 1 byte, rxLen=1
3. The driver will transmit the txData, and after completion of txData begin to recieve data, padding MOSI with DefaultTXData

Enumerator
SPI_WIDTH_3WIRE	1 Data line, half duplex
SPI_WIDTH_STANDARD	MISO/MOSI, full duplex.
SPI_WIDTH_DUAL	2 Data lines, half duplex
SPI_WIDTH_QUAD	4 Data lines, half duplex

Function Documentation

MXC_SPI_AbortAsync()

void MXC_SPI_AbortAsync

(

mxc_spi_regs_t *

spi

)

Abort any asynchronous requests in progress.

Abort any asynchronous requests in progress. Any callbacks associated with the active transaction will be executed to indicate when the transaction has been terminated.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

MXC_SPI_AbortTransmission()

int MXC_SPI_AbortTransmission

(

mxc_spi_regs_t *

spi

)

Aborts an ongoing SPI Transmission.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_AsyncHandler()

void MXC_SPI_AsyncHandler

(

mxc_spi_regs_t *

spi

)

The processing function for asynchronous transactions.

When using the asynchronous functions, the application must call this function periodically. This can be done from within the SPI interrupt handler or periodically by the application if SPI interrupts are disabled.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

MXC_SPI_ClearFlags()

void MXC_SPI_ClearFlags

(

mxc_spi_regs_t *

spi

)

Clears the interrupt flags that are currently set.

These functions should not be used while using non-blocking Transaction Level functions (Async or DMA)

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

MXC_SPI_ClearRXFIFO()

void MXC_SPI_ClearRXFIFO

(

mxc_spi_regs_t *

spi

)

Removes and discards all bytes currently in the receive FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

MXC_SPI_ClearTXFIFO()

void MXC_SPI_ClearTXFIFO

(

mxc_spi_regs_t *

spi

)

Removes and discards all bytes currently in the transmit FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

MXC_SPI_DisableInt()

void MXC_SPI_DisableInt	(	mxc_spi_regs_t *	spi,
		unsigned int	mask
	)

Disables specific interrupts.

These functions should not be used while using non-blocking Transaction Level functions (Async or DMA)

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
mask	The interrupts to be disabled

MXC_SPI_EnableInt()

void MXC_SPI_EnableInt	(	mxc_spi_regs_t *	spi,
		unsigned int	mask
	)

Enables specific interrupts.

These functions should not be used while using non-blocking Transaction Level functions (Async or DMA)

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
mask	The interrupts to be enabled

MXC_SPI_GetActive()

int MXC_SPI_GetActive

(

mxc_spi_regs_t *

spi

)

Checks the SPI Peripheral for an ongoing transmission.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Active/Inactive, see Error Codes for a list of return codes.

MXC_SPI_GetDataSize()

int MXC_SPI_GetDataSize

(

mxc_spi_regs_t *

spi

)

Gets the number of bits per character.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_GetFlags()

unsigned int MXC_SPI_GetFlags

(

mxc_spi_regs_t *

spi

)

Gets the interrupt flags that are currently set.

These functions should not be used while using non-blocking Transaction Level functions (Async or DMA)

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The interrupt flags

MXC_SPI_GetFrequency()

unsigned int MXC_SPI_GetFrequency

(

mxc_spi_regs_t *

spi

)

Get the frequency of the SPI interface.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The SPI bus frequency in Hertz

MXC_SPI_GetMode()

mxc_spi_mode_t MXC_SPI_GetMode

(

mxc_spi_regs_t *

spi

)

Gets the spi mode.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

mxc_spi_mode_t mxc_spi_mode_t

MXC_SPI_GetPeripheralClock()

int MXC_SPI_GetPeripheralClock

(

mxc_spi_regs_t *

spi

)

Returns the frequency of the clock used as the bit rate generator for a given SPI instance.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Frequency of the clock used as the bit rate generator

MXC_SPI_GetRXFIFOAvailable()

unsigned int MXC_SPI_GetRXFIFOAvailable

(

mxc_spi_regs_t *

spi

)

Get the number of bytes currently available in the receive FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The number of bytes available.

MXC_SPI_GetRXThreshold()

unsigned int MXC_SPI_GetRXThreshold

(

mxc_spi_regs_t *

spi

)

Get the current receive threshold level.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The receive threshold value (in bytes).

MXC_SPI_GetSlave()

int MXC_SPI_GetSlave

(

mxc_spi_regs_t *

spi

)

Gets the slave select (SS) line used for transmissions.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

slave slect

MXC_SPI_GetTXFIFOAvailable()

unsigned int MXC_SPI_GetTXFIFOAvailable

(

mxc_spi_regs_t *

spi

)

Get the amount of free space available in the transmit FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The number of bytes available.

MXC_SPI_GetTXThreshold()

unsigned int MXC_SPI_GetTXThreshold

(

mxc_spi_regs_t *

spi

)

Get the current transmit threshold level.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

The transmit threshold value (in bytes).

MXC_SPI_GetWidth()

mxc_spi_width_t MXC_SPI_GetWidth

(

mxc_spi_regs_t *

spi

)

Gets the SPI width used for transmissions.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Spi Width mxc_spi_width_t

MXC_SPI_HWSSControl()

void MXC_SPI_HWSSControl	(	mxc_spi_regs_t *	spi,
		int	state
	)

Enable/Disable HW CS control feature.

Depending on the application, the user might need to manually drive the slave select pin. The SPI driver automatically drives the SS pin and this function enables/disables this feature.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
state	Non-zero values: enable HW SS mode. Zero: disable HW SS mode.

MXC_SPI_Init()

int MXC_SPI_Init	(	mxc_spi_regs_t *	spi,
		int	masterMode,
		int	quadModeUsed,
		int	numSlaves,
		unsigned	ssPolarity,
		unsigned int	hz
	)

Initialize and enable SPI peripheral.

This function initializes everything necessary to call a SPI transaction function. Some parameters are set to defaults as follows: SPI Mode - 0 SPI Width - SPI_WIDTH_STANDARD (even if quadModeUsed is set)

Note

On default this function enables SPI peripheral clock and spi gpio pins. if you wish to manage clock and gpio related things in upper level instead of here. Define MSDK_NO_GPIO_CLK_INIT flag in project.mk file. By this flag this function will remove clock and gpio related codes from file.

These parameters can be modified after initialization using low level functions

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
masterMode	Whether to put the device in master or slave mode. Use non-zero for master mode, and zero for slave mode.
quadModeUsed	Whether to obtain control of the SDIO2/3 pins. Use non-zero if the pins are needed (if Quad Mode will be used), and zero if they are not needed (quad mode will never be used).
numSlaves	The number of slaves used, if in master mode. This is used to obtain control of the necessary SS pins. In slave mode this is ignored and SS1 is used.
ssPolarity	This field sets the SS active polarity for each slave, each bit position corresponds to each SS line.
hz	The requested clock frequency. The actual clock frequency will be returned by the function if successful. Used in master mode only.

Returns

If successful, the actual clock frequency is returned. Otherwise, see Error Codes for a list of return codes.

MXC_SPI_MasterTransaction()

int MXC_SPI_MasterTransaction

(

mxc_spi_req_t *

req

)

Performs a blocking SPI transaction.

Performs a blocking SPI transaction. These actions will be performed in Master Mode:

1. Assert the specified SS
2. In Full Duplex Modes, send TX data while receiving RX Data if rxLen > txLen, pad txData with DefaultTXData if txLen > rxLen, discard rxData where rxCnt > rxLen
3. In Half Duplex Modes, send TX Data, then receive RX Data
4. Deassert the specified SS

These actions will be performed in Slave Mode:

1. Fill FIFO with txData
2. Wait for SS Assert
3. If needed, pad txData with DefaultTXData
4. Unload RX FIFO as needed
5. On SS Deassert, return

Parameters

req	Pointer to details of the transaction

Returns

See Error Codes for the list of error return codes.

MXC_SPI_MasterTransactionAsync()

int MXC_SPI_MasterTransactionAsync

(

mxc_spi_req_t *

req

)

Setup an interrupt-driven SPI transaction.

The TX FIFO will be filled with txData, padded with DefaultTXData if necessary Relevant interrupts will be enabled, and relevant registers set (SS, Width, etc)

Parameters

req	Pointer to details of the transaction

Returns

See Error Codes for the list of error return codes.

MXC_SPI_MasterTransactionDMA()

int MXC_SPI_MasterTransactionDMA

(

mxc_spi_req_t *

req

)

Setup a DMA driven SPI transaction.

The TX FIFO will be filled with txData, padded with DefaultTXData if necessary Relevant interrupts will be enabled, and relevant registers set (SS, Width, etc)

The lowest-indexed unused DMA channel will be acquired (using the DMA API) and set up to load/unload the FIFOs with as few interrupt-based events as possible. The channel will be reset and returned to the system at the end of the transaction.

Parameters

req	Pointer to details of the transaction

Returns

See Error Codes for the list of error return codes.

MXC_SPI_ReadRXFIFO()

unsigned int MXC_SPI_ReadRXFIFO	(	mxc_spi_regs_t *	spi,
		unsigned char *	bytes,
		unsigned int	len
	)

Unloads bytes from the receive FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
bytes	The buffer to read the data into.
len	The number of bytes to read.

Returns

The number of bytes actually read.

MXC_SPI_ReadyForSleep()

int MXC_SPI_ReadyForSleep

(

mxc_spi_regs_t *

spi

)

Checks if the given SPI bus can be placed in sleep mode.

This functions checks to see if there are any on-going SPI transactions in progress. If there are transactions in progress, the application should wait until the SPI bus is free before entering a low-power state.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

E_NO_ERROR if ready, and non-zero if busy or error. See Error Codes for the list of error return codes.

MXC_SPI_SetDataSize()

int MXC_SPI_SetDataSize	(	mxc_spi_regs_t *	spi,
		int	dataSize
	)

Sets the number of bits per character.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
dataSize	The number of bits per character

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetDefaultTXData()

int MXC_SPI_SetDefaultTXData	(	mxc_spi_regs_t *	spi,
		unsigned int	defaultTXData
	)

Sets the TX data to transmit as a 'dummy' byte.

In single wire master mode, this data is transmitted on MOSI when performing an RX (MISO) only transaction. This defaults to 0.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
defaultTXData	Data to shift out in RX-only transactions

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetFrequency()

int MXC_SPI_SetFrequency	(	mxc_spi_regs_t *	spi,
		unsigned int	hz
	)

Set the frequency of the SPI interface.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
hz	The desired frequency in Hertz.

Returns

Negative if error, otherwise actual speed set. See Error Codes for the list of error return codes.

MXC_SPI_SetMode()

int MXC_SPI_SetMode	(	mxc_spi_regs_t *	spi,
		mxc_spi_mode_t	spiMode
	)

Sets the spi mode using clock polarity and clock phase.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
spiMode	mxc_spi_mode_t

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetRXThreshold()

int MXC_SPI_SetRXThreshold	(	mxc_spi_regs_t *	spi,
		unsigned int	numBytes
	)

Set the receive threshold level.

RX FIFO Receive threshold. Smaller values will cause interrupts to occur more often, but reduce the possibility of losing data because of a FIFO overflow. Larger values will reduce the time required by the ISR, but increase the possibility of data loss. Passing an invalid value will cause the driver to use the value already set in the appropriate register.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
numBytes	The threshold level to set. This value must be between 0 and 30 inclusive.

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetSlave()

int MXC_SPI_SetSlave	(	mxc_spi_regs_t *	spi,
		int	ssIdx
	)

Sets the slave select (SS) line used for transmissions.

This function is applicable in Master mode only

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
ssIdx	Slave select index

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetTXThreshold()

int MXC_SPI_SetTXThreshold	(	mxc_spi_regs_t *	spi,
		unsigned int	numBytes
	)

Set the transmit threshold level.

TX FIFO threshold. Smaller values will cause interrupts to occur more often, but reduce the possibility of terminating a transaction early in master mode, or transmitting invalid data in slave mode. Larger values will reduce the time required by the ISR, but increase the possibility errors occurring. Passing an invalid value will cause the driver to use the value already set in the appropriate register.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
numBytes	The threshold level to set. This value must be between 0 and 30 inclusive.

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SetWidth()

int MXC_SPI_SetWidth	(	mxc_spi_regs_t *	spi,
		mxc_spi_width_t	spiWidth
	)

Sets the SPI width used for transmissions.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
spiWidth	SPI Width (3-Wire, Standard, Dual SPI, Quad SPI)

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_Shutdown()

int MXC_SPI_Shutdown

(

mxc_spi_regs_t *

spi

)

Disable and shutdown SPI peripheral.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_SlaveTransaction()

int MXC_SPI_SlaveTransaction

(

mxc_spi_req_t *

req

)

Performs a blocking SPI transaction.

Performs a blocking SPI transaction. These actions will be performed in Slave Mode:

1. Fill FIFO with txData
2. Wait for SS Assert
3. If needed, pad txData with DefaultTXData
4. Unload RX FIFO as needed
5. On SS Deassert, return

Parameters

req	Pointer to details of the transaction

Returns

See Error Codes for the list of error return codes.

MXC_SPI_SlaveTransactionAsync()

int MXC_SPI_SlaveTransactionAsync

(

mxc_spi_req_t *

req

)

Setup an interrupt-driven SPI transaction.

The TX FIFO will be filled with txData, padded with DefaultTXData if necessary Relevant interrupts will be enabled, and relevant registers set (SS, Width, etc)

Parameters

req	Pointer to details of the transactionz

Returns

See Error Codes for the list of error return codes.

MXC_SPI_SlaveTransactionDMA()

int MXC_SPI_SlaveTransactionDMA

(

mxc_spi_req_t *

req

)

Setup a DMA driven SPI transaction.

The TX FIFO will be filled with txData, padded with DefaultTXData if necessary Relevant interrupts will be enabled, and relevant registers set (SS, Width, etc)

The lowest-indexed unused DMA channel will be acquired (using the DMA API) and set up to load/unload the FIFOs with as few interrupt-based events as possible. The channel will be reset and returned to the system at the end of the transaction.

Parameters

req	Pointer to details of the transaction

Returns

See Error Codes for the list of error return codes.

MXC_SPI_StartTransmission()

int MXC_SPI_StartTransmission

(

mxc_spi_regs_t *

spi

)

Starts a SPI Transmission.

This function is applicable in Master mode only

The user must ensure that there are no ongoing transmissions before calling this function

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)

Returns

Success/Fail, see Error Codes for a list of return codes.

MXC_SPI_WriteTXFIFO()

unsigned int MXC_SPI_WriteTXFIFO	(	mxc_spi_regs_t *	spi,
		unsigned char *	bytes,
		unsigned int	len
	)

Loads bytes into the transmit FIFO.

Parameters

spi	Pointer to SPI registers (selects the SPI block used.)
bytes	The buffer containing the bytes to write
len	The number of bytes to write.

Returns

The number of bytes actually written.