stevefielding / spi_isr

Arduino library to support SPI Interrupt Service Routine on ATSAM3X

spi_isr

Arduino library to support spi slave interrupt service routines.
Hard coded for SPI0 on ATSAM3X (ie Arduino Due).
Tested with ATSAM3X and Raspberry Pi. See spi master test code for the RPi in the python directory. You will need to do the following in order to use this library:

1. Include <spi_isr.h> and <SPI.h>
2. From setup, call spi_isr_init() with the pin number used for spi chip select.
3. Implement two functions, readRegs() and writeRegs(). These functions transfer data to and from the data buffers defined in the library.
4. link readRegs() and writeRegs() to virtual functions defined in the library.
5. Link SPI0_Handler().
6. From loop, call spi_update_regs().

Read and write requests must be formed into a series of messages.
READ_INIT and WRITE_INIT messages allow the user to initialize a read or write, specifying the data length and address.
The ISR does not actually read or write data to the users registers. This must be performed in a regularly scheduled function call, which tests for read or write requests, and copies data to or from a buffer that is local to the isr.
The user must ensure that they call the spi_update_regs function from their main loop. Then spi_update_regs will check to determine if there is data to be read or written and call readRegs or writeRegs if required.

Control message commands:

Command	Value	Description
WRITE_INIT	0x0	Request a write of x data bytes to address y
READ_INIT	0x1	Request a read of x data bytes from address y
DATA_ACCESS	0x2	Read or write the data
STATUS_READ	0x3	Check the status of the last operation

Error codes returned by STATUS_READ:

Error	Mask	Description
RX_RDY_SPI_STATUS_MASK	0x1	Receive data has been read and is ready for transfer
WR_COMP_SPI_STATUS_MASK	0x2	Write data has been written
RX_OVR_SPI_STATUS_MASK	0x4	SPI receive over run error
TX_UNDR_SPI_STATUS_MASK	0x8	SPI transmit under run error
WR_REG_ERROR_SPI_STATUS_MASK	0x10	Unspecified write error
RD_REG_ERROR_SPI_STATUS_MASK	0x20	Unspecified read error

Individual messages can be combined into read and write data sequences

Read sequence

1. READ_INIT
2. STATUS_READ
3. DATA_ACCESS

Write sequence

1. WRITE_INIT
2. DATA_ACCESS
3. STATUS_READ

Examples of each message type:

WRITE_INIT or READ_INIT:

MOSI	MISO
SYNC1_NIBBLE, READ/WRITE_INIT	0x0
SYNC2_NIBBLE, dataLen[11:8]	0x0
dataLen[7:0]	0x0
address[15:8]	0x0
address[7:0]	0x0

DATA_ACCESS:

If the previous message was a WRITE_INIT then the data is in MOSI, else if the previous message was a READ_INIT then the data is in MISO

MOSI	MISO
SYNC1_NIBBLE, DATA_ACCESS	0x0
SYNC2_NIBBLE, 0x0	0x0
data0	data0
data1	data1
.	.
.	.
.	.
dataN	dataN

STATUS_READ:

MOSI	MISO
SYNC1_NIBBLE, STATUS_READ	0x0
SYNC2_NIBBLE, 0x0	0x0
0x0	status

Constant definitions

SYNC1_NIBBLE 0x50 SYNC2_NIBBLE 0xa0

Implementing readRegs and writeRegs

You will need to over-ride the virtual functions, readMyRegs and writeMyRegs, and then create a link to your own functions.
These functions will be called when you call spi_update_regs from your main loop. It is entirely up to the user to decide how to interpret the address and how to combine bytes into 16-bit and 32-bit values.
readMyRegs and writeMyRegs take a 16-bit data length, 16-bit address, and a pointer to a byte data array.
'readMyRegs': Read 'length' bytes of user data and copy to the 'data' array. The bool return value should indicate if the read was successful.
'writeMyRegs': Write 'length' bytes of data from 'data' array to user data.

You will also need to link the class implemented SPI0_Handler to SPI0_Handler, call spi_isr_init from setup.

See example project.