Unit SPI

Return to Unit Reference

Description

---

SPI (Serial Peripheral Interface) is a synchronous serial bus for communication with peripheral components.

The SPI protocol is not defined by any actual standard but some psuedo standards exist with all of the available devices. SPI is a master-slave protocol where the master asserts the chip selectline (CS) to select the slave device before sending data one byte at a time. For every byte written to the bus by the master the selected slave returns a byte as well so for every write there is an equivalent read. SPI can also operate in either 4 wire (standard) or 3 wire(bidirectional) modes.

Due to the lack of formal standards and the range of devices that exist various options are provided to allow setting clock phase and polarity as well chip select polarity.

For the purpose of this interface a device is the SPI controller attached to the local system and may be either a master or a slave. Since the protocol does not include any form of enumeration or identification the interface does not attempt to represent the devices connected to the bus, any driver written to communicate with a connected SPI device should know (or allow configuration of) the chip select for the for the device and the specific message format required for that device.

Constants

---

To be documented

Type definitions

---

To be documented

Public variables

---

To be documented

Function declarations

---

Initialization functions

procedure SPIInit;

Description: Initialize the SPI unit and SPI device table

Note	Called only during system startup

SPI functions

function SPIDeviceStart(SPI:PSPIDevice; Mode,ClockRate,ClockPhase,ClockPolarity:LongWord):LongWord;

Description: Start the specified SPI device ready for writing and reading

SPI	The SPI device to start
Mode	The device mode to set (eg SPI_MODE_4WIRE)
ClockRate	The clock rate to set for the device
ClockPhase	The clock phase to set (eg SPI_CLOCK_PHASE_LOW)
ClockPolarity	The clock polarity to set (eg SPI_CLOCK_POLARITY_LOW)
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceStop(SPI:PSPIDevice):LongWord;

Description: Stop the specified SPI device and terminate writing and reading

SPI	The SPI device to stop
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceWrite(SPI:PSPIDevice; ChipSelect:Word; Source:Pointer; Size,Flags:LongWord; var Count:LongWord):LongWord;

Description: Write data to the specified SPI device

SPI	The SPI device to write to
ChipSelect	The chip select for the slave to write to (eg SPI_CS_0)
Source	Pointer to a buffer of data to transmit
Size	The size of the buffer
Flags	The flags for this transfer (eg SPI_TRANSFER_DMA)
Count	The number of bytes written on return
Return	ERROR_SUCCESS if completed or another error code on failure
Note	Because SPI writes and then reads for each byte, received data will be discarded for each by written

function SPIDeviceSetMode(SPI:PSPIDevice; Mode:LongWord):LongWord;

Description: Set the device mode for the specified SPI device

SPI	The SPI device to set device mode for
Mode	The device mode to set (eg SPI_MODE_4WIRE)
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceSetClockRate(SPI:PSPIDevice; ClockRate:LongWord):LongWord;

Description: Set the clock rate for the specified SPI device

SPI	The SPI device to set clock rate for
ClockRate	The clock rate to set in Hz
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceSetClockPhase(SPI:PSPIDevice; ClockPhase:LongWord):LongWord;

Description: Set the clock phase for the specified SPI device

SPI	The SPI device to set clock phase for
ClockPhase	The clock phase to set (eg SPI_CLOCK_PHASE_LOW)
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceSetClockPolarity(SPI:PSPIDevice; ClockPolarity:LongWord):LongWord;

Description: Set the clock polarity for the specified SPI device

SPI	The SPI device to set clock polarity for
ClockPolarity	The clock polarity to set (eg SPI_CLOCK_POLARITY_LOW)
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceSetSelectPolarity(SPI:PSPIDevice; ChipSelect:Word; SelectPolarity:LongWord):LongWord;

Description: Set the chip select polarity for the specified SPI device

SPI	The SPI device to set chip select polarity for
ChipSelect	The chip select number to set polarity for (SPI_CS_NONE for default)
SelectPolarity	The chip select polarity to set (eg SPI_CS_POLARITY_LOW)
Return	ERROR_SUCCESS if completed or another error code on failure

function SPIDeviceCreate:PSPIDevice;

Description: Create a new SPI entry

Return	Pointer to new SPI entry or nil if SPI could not be created

function SPIDeviceCreateEx(Size:LongWord):PSPIDevice;

Description: Create a new SPI entry

Size	Size in bytes to allocate for new SPI (Including the SPI entry)
Return	Pointer to new SPI entry or nil if SPI could not be created

function SPIDeviceDestroy(SPI:PSPIDevice):LongWord;

Description: Destroy an existing SPI entry

Note	To be documented

function SPIDeviceRegister(SPI:PSPIDevice):LongWord;

Description: Register a new SPI in the SPI table

Note	To be documented

function SPIDeviceFind(SPIId:LongWord):PSPIDevice;

Description: To be documented

Note	To be documented

function SPIDeviceFindByName(const Name:String):PSPIDevice; inline;

Description: To be documented

Note	To be documented

function SPIDeviceFindByDescription(const Description:String):PSPIDevice; inline;

Description: To be documented

Note	To be documented

Return to Unit Reference