SPI Execute-In-Place Flash Controller (SPI XIP)

The SPI XIP controller attaches a SPI NOR flash device and exposes its contents as an ordinary memory-mapped window, so instructions and data can be fetched directly with load instructions (execute-in-place). Alongside the read window, a register-driven command engine performs the operations that XIP reads cannot: programming, erasing, and device configuration. The engine issues arbitrary flash opcodes, optionally wrapping them in a write-enable (WREN) sequence and polling the status register until the device is ready again.

Features

• Memory-mapped execute-in-place (XIP) read window - direct load access to flash

• Configurable SPI transfer mode and read dummy cycles

• Generic flash-command engine: opcode, optional 24-bit address and program payload

• Optional automatic WREN wrapper and busy-polling around a command

• Software-filled TX FIFO supplying program data bytes

• Enhanced Volatile Configuration Register (EVCR) setup

• Status register exposing busy state, the device status byte, and TX FIFO space

Command Engine

A programming or erase operation is issued through the command registers:

1. Write command with the flash opcode and the hasAddress, needsWren and needsPoll flags.

2. If the opcode takes an address, write address; if it carries a payload, write the byte count to length and push the bytes to tx_data.

3. Write start. The engine optionally sends WREN, sends the opcode (+ address + payload), and, when needsPoll is set, polls the status register until the write is complete.

Poll the busy bit of status (or the device status byte) to detect completion. Device configuration - the SPI mode, dummy cycles and the EVCR - is applied by writing config and triggering configure.

Configuration

Available bus architectures:

• APB3

• TileLink

• Wishbone

By default, all buses are defined with 12 bit address and 32 bit data width.

Parameter

SpiXipControllerCtrl parameters

Name	Type	Description	Default
p	SpiControllerCtrl.Parameter	Underlying SPI controller parameter. Use Parameter.xip() for the XIP preset.
dataWidth	Int	SPI data-path width in bits.
txFifoDepth	Int	Depth of the software-filled program-data FIFO.	64

Register Mapping

IP Identification:

The register map starts with an IP Identification block to provide all information about the underlying IP core to software drivers. This allows to provide backwards compatible drivers.

IP Identification Registers

Address	Bit	Field	Default	Permission	Description
0x000	31 - 24	API	0x0	Rx	API version of the implemented IP Identification.
	23 - 16	Length	0x8	Rx	Length of the IP Identification block in Bytes.
	15 - 0	ID	0x07	Rx	IP value of this IP core.
0x004	31 - 24	Major Version	0x1	Rx	Major number if this IP core. Version schema is major.minor.patch.
	23 - 16	Minor Version	0x1	Rx	Minor number if this IP core. Version schema is major.minor.patch.
	15 - 0	Patch Version	0x0	Rx	Patch number if this IP core. Version schema is major.minor.patch.

Control Registers

Address	Bit	Field	Default	Permission	Description
0x008		configure		xW	Write any value to apply config (SPI mode, dummy cycles, EVCR) to the device.
0x00C	23 - 16	evcr	0x0	RW	Enhanced Volatile Configuration Register value written during configure.
	15 - 8	dummy_cycles	0x0	RW	Number of dummy cycles for read commands.
	7 - 0	mode	0x0	RW	SPI transfer mode selector.
0x010	10	needs_poll	0x0	RW	Poll the status register until the device is ready after the command.
	9	needs_wren	0x0	RW	Wrap the command in a write-enable (WREN) sequence.
	8	has_address	0x0	RW	The opcode is followed by the 24-bit address.
	7 - 0	opcode	0x0	RW	Flash command opcode.
0x014	23 - 0	address	0x0	RW	Flash address for address-bearing commands.
0x018	8 - 0	length	0x0	RW	Number of program-data bytes to send from the TX FIFO.
0x01C		start		xW	Write any value to launch the command described by the registers above.
0x020	7 - 0	tx_data		xW	Push one program-data byte into the TX FIFO.
0x024	31 - 16	tx_availability		Rx	Free entries in the program-data TX FIFO.
	15 - 8	status_reg	0x0	Rx	Last-read device status byte.
	0	busy	0x0	Rx	High while a command is in progress.