Unit SPI

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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


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