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\documentclass{gqtekspec}

\project{Quad SPI Flash Controller}

\title{Specification}

\author{Dan Gisselquist, Ph.D.}

\email{dgisselq\at opencores.org}

\revision{Rev.~0.1}

\begin{document}

\pagestyle{gqtekspecplain}

\titlepage

\begin{license}

Copyright (C) \theyear\today, Gisselquist Technology, LLC

This project is free software (firmware): you can redistribute it and/or

modify it under the terms of  the GNU General Public License as published

by the Free Software Foundation, either version 3 of the License, or (at

your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT

ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

for more details.

You should have received a copy of the GNU General Public License along

with this program.  If not, see \hbox{<http://www.gnu.org/licenses/>} for a copy.

\end{license}

\begin{revisionhistory}

0.1 & 5/13/2015 & Gisselquist & First Draft \\\hline

\end{revisionhistory}

% Revision History

% Table of Contents, named Contents

\tableofcontents

\listoffigures

\listoftables

\begin{preface}

The genesis of this project was a desire to communicate with and program an

FPGA board without the need for any proprietary tools.  This includes Xilinx

JTAG cables, or other proprietary loading capabilities such as Digilent's

Adept program.  As a result, all interactions with the board need to take

place using open source tools, and the board must be able to reprogram itself.

\end{preface}

\chapter{Introduction}

\pagenumbering{arabic}

\setcounter{page}{1}

The Quad SPI Flash controller handles all necessary queries and accesses to

and from a SPI Flash device that has been augmented with an additional

two data lines and enabled with a mode allowing all four data lines to

work together in the same direction at the same time.  Since the interface

was derived from a SPI interface, most of the interaction takes place using

normal SPI protocols and only some commands work at the higher four bits

at a time speed.

This particular controller attempts to mask the underlying operation of the

SPI device behind a wishbone interface, to make it so that reads and writes

are as simple as using the wishbone interface.  However, the difference

between erasing (turning bits from '0' to '1') and programming (turning bits

from '1' to '0') breaks this model somewhat.  Therefore, reads from the

device act like normal wishbone reads, writes program the device and

sort of work with the wishbone, while erase commands require another register

to control.  Please read the Operations chapter for a detailed description

of how to perform these relevant operations.

This controller implements the interface for the Quad SPI flash found on the

Basys-3 board built by Digilent, Inc.  Some portions of the interface may

be specific to the Spansion S25FL032P chip used on this board, and the

100~MHz system clock found on the board, although there is no reason the

controller needs to be limited to this architecture.  It just happens to be

the one I have been designing to and for.

For a description of how the internals of this core work, feel free to browse

through the Architecture chapter.

The registers that control this core are discussed in the Registers chapter.

As required, you can find a wishbone datasheet in Chapt.~\ref{chap:wishbone}.

The final pertinent information for implementing this core is found in the

I/O Ports chapter, Chapt.~\ref{chap:ioports}.

As always, write me if you have any questions or problems.

\chapter{Architecture}\label{chap:arch}

As built, the core consists of only two components: the wishbone quad SPI

flash controller, {\tt wbqspiflash}, and the lower level quad SPI driver,

{\tt llqspi}.  The controller issues high level read/write commands to the

lower level driver, which actually implements the Quad SPI protocol.

Pictorally, this looks something like Fig.~\ref{fig:arch}.

\begin{figure}\begin{center}\begin{pspicture}(-2in,0)(2in,3.5in)

\rput(0,2.5in){

        \rput(-0.9in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.92in,0.5in){\tt i\_wb\_cyc}

        \rput(-0.7in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.72in,0.5in){\tt i\_wb\_data\_stb}

        \rput(-0.5in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.52in,0.5in){\tt i\_wb\_ctrl\_stb}

        \rput(-0.3in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.32in,0.5in){\tt i\_wb\_we}

        \rput(-0.1in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.12in,0.5in){\tt i\_wb\_addr}

        \rput( 0.1in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}( 0.08in,0.5in){\tt i\_wb\_data}

        %

        \rput( 0.5in,0){\psline{<-}(0,1in)(0,0in)}

                \rput[b]{90}( 0.48in,0.5in){\tt o\_wb\_ack}

        \rput( 0.7in,0){\psline{<-}(0,1in)(0,0in)}

                \rput[b]{90}( 0.68in,0.5in){\tt o\_wb\_stall}

        \rput( 0.9in,0){\psline{<-}(0,1in)(0,0in)}

                \rput[b]{90}( 0.88in,0.5in){\tt o\_wb\_data}}

\rput(0,2.0in){%

        \rput(0,0){\psframe(-1.2in,0)(1.2in,0.5in)}

        \rput(0,0.25in){\tt wbqspiflash}}

\rput(0,1.0in){

        \rput(-0.9in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.92in,0.5in){\tt spi\_wr}

        \rput(-0.7in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.72in,0.5in){\tt spi\_hold}

        \rput(-0.5in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.52in,0.5in){\tt spi\_in}

        \rput(-0.3in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.32in,0.5in){\tt spi\_len}

        \rput(-0.1in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}(-0.12in,0.5in){\tt spi\_spd}

        \rput( 0.1in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}( 0.08in,0.5in){\tt spi\_dir}

        % \rput(-0.9in,0){\psline{->}(0,1in)(0,0in)}

                % \rput[b]{90}(-0.92in,0.5in){\tt i\_wb\_cyc}

        \rput( 0.5in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}( 0.48in,0.5in){\tt spi\_out}

        \rput( 0.7in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}( 0.68in,0.5in){\tt spi\_valid}

        \rput( 0.9in,0){\psline{->}(0,1in)(0,0in)}

                \rput[b]{90}( 0.88in,0.5in){\tt spi\_busy}}

\rput(0,0.5in){

        \rput(0,0){\psframe(-1.25in,0)(1.25in,0.5in)}

        \rput(0,0.25in){\tt llqspi}}

        \rput(0,0){\psline{<->}(-0.3in,0.5in)(-0.3in,0)

                \psline{<->}(-0.1in,0.5in)(-0.1in,0)

                \psline{<->}(0.1in,0.5in)(0.1in,0)

                \psline{<->}(0.3in,0.5in)(0.3in,0)}

        \rput[l](0.4in,0.25in){Quad SPI I/O lines}

\end{pspicture}\end{center}

\caption{Architecture Diagram}\label{fig:arch}

\end{figure}

This is also what you will find if you browse through the code.

While it isn't relevant for operating the device, a quick description of these

internal wires may be educational.  The lower level device is commanded by

asserting a {\tt spi\_wr} signal when the device is not busy (i.e. {\tt

spi\_busy} is low).  The actual command given depends upon the other

signals.  {\tt spi\_len} is a two bit value indicating whether this is an

8 bit (2'b00), 16 bit (2'b01), 24 bit (2'b10), or 32 bit (2'b11) transaction.

The data to be sent out the port is placed into {\tt spi\_in}.

Further, to support Quad I/O, {\tt spi\_spd} can be set to one to use all four

bits.  In this case, {\tt spi\_dir} must also be set to either 1'b0 for

writing, or 1'b1 to read from the four bits.

When data is valid from the lower level driver, the {\tt spi\_valid} line

will go high and {\tt spi\_out} will contain the data with the most recently

read bits in the lower bits.  Further, when the device is idle, {\tt spi\_busy}

will go low, where it may then read another command.

Sadly, this simple interface as originally designed doesn't work on a

device where transactions can be longer than 32~bits.  To support these

longer transactions, the lower level driver checks the {\tt spi\_wr} line

before it finishes any transaction.  If the line is high, the lower level

driver will deassert {\tt spi\_busy} for one cycle while reading the command

from the controller on the previous cycle.  Further, the controller can also

assert the {\tt spi\_hold} line which will stop the clock to the device

and force everything to wait for further instructions.

This hold line interface was necessary to deal with a slow wishbone bus that

was writing to the device, but that didn't have it's next data line ready.

Thus, by holding the {\tt i\_wb\_cyc} line high, a write could take many

clocks and the flash would simply wait for it.  (I was commanding the device

via a serial port, so writes could take {\em many} clock cycles for each

word to come through, i.e. 1,500 clocks or so per word and that's at high

speed.)

The upper level component, the controller {\tt wbqspiflash}, is little more

than a glorified state machine that interacts with the wishbone bus.

From it's idle state, it can handle any command, whether data or control,

and issue appropriate commands to the lower level driver.  From any other

state, it will stall the bus until it comes back to idle--with a few exceptions.

Subsequent data reads, while reading data, will keep the device reading.

Subsequent data writes, while in program mode, will keep filling the devices

buffer before starting the write.  In other respects, the device will just

stall the bus until it comes back to idle.

While they aren't used in this design, the wishbone error and retry signals

would've made a lot of sense here.  Specifically, it should be an error to

read from the device while it is in the middle of an erase or program command.

Instead, this core stalls the bus--trying to do good for everyone.  Perhaps

a later, updated, implementation will make better use of these signals instead

of stalling.  For now, this core just stalls the bus.

Perhaps the best takeaway from this architecture section is that the varying

pieces of complexity have each been separated from each other.  There's a

lower level driver that handles actually toggling the lines to the port,

while the higher level driver maintains the state machine controlling which

commands need to be issued and when.

\chapter{Operation}\label{chap:ops}

This implementation attempts to encapsulate (hide) the details of the chip

from the user, so that the user does not need to know about the various

subcommands going to and from the chip.  The original goal was to make the

chip act like any other read/write memory, however the difference between

erasing and programming the chip made this impossible.  Therefore a separate

register is given to erase any given sector, while reads and writes may proceed

(almost) as normal.

The wishbone bus that this controller works with, however, is a 32--bit

bus.  Address one on the bus addresses a completely different 32--bit word

from address zero or address two.  Bus select lines are not implemented,

all operations are 32--bit.  Further, the device is little--endian, meaning

that the low order byte is the first byte that will be or is stored on the

flash.

\section{High Level}

From a high level perspective, this core provides read/write access to the

device either via the wishbone (read and program), or through a control

register found on the wishbone (the EREG).  Programming the device consists of

first erasing the region of interest.  This will set all the bits to '1' in

that region.  After erasing the region, the region can then be programmed,

setting some of the '1' bits to '0's.  When neither erase nor program

operation is going on, the device may be read.  The section will describe

each of those operations in detail.

To erase a sector of the device, two writes are required to the EREG register.

The first write turns off the write protect bit, whereas the second write

commands the erase itself.  The first write should equal \hbox{0x1000\_0000},

the second should be any address within the sector to be erased together

with setting the high bit of the register or \hbox{0x8000\_0000} plus the

address.  After this second write, the controller will issue a write--enable

command to the device, followed by a sector erase command.  In summary,

\begin{enumerate}

\item Disable write protect by writing \hbox{\tt 0x1000\_0000} to the EREG

        register

\item Command the erase by writing \hbox{\tt 0x8000\_0000} plus the device

        address to the EREG register.  (Remember, this is the {\em word

        address} of interest, not the {\em byte address}.)

\end{enumerate}

While the device is erasing, the controller will idle while checking the

status register over and over again.  Should you wish to read from the EREG

during this time, the high order bit of the EREG register will be set.

Once the erase is complete, this bit will clear, the interrupt line will

be strobed high, and other operations may take then place on the part.  Any

attempt to perform another operation on the part prior to that time will stall

the bus until the erase is complete.

Once an area has been erased, it may then be programmed.  To program the device,

first disable the write protect by writing a {\tt 0x1000\_0000} to the EREG

register.  After that, you may then write to the area in question whatever

values you wish to program.  One 256~byte (64~bus word) page may be programmed

at a time.  Pages start on even boundaries, such as addresses {\tt 0x040},

{\tt 0x080}, {\tt 0x0100}, etc.  To program a whole page at a time, write the

64~words of the page to the controller without dropping the {\tt i\_wb\_cyc}

line.  Attempts to write more than 64~words will stall the bus, as will

attempts to write more than one page.  Writes of less than a page work as well.

In summary,

\begin{enumerate}

\item Disable the write protect by writing a {\tt 0x1000\_0000} to the EREG

        register.

\item Write the page of interest to the data memory of the device.

        The first address should start at the beginning of a page (bottom six

        bits zero), and end at the end of the page (bottom six bits one, top

        bits identical).  Writes of less than a page are okay.  Writes crossing

        page boundaries will stall the device.

\end{enumerate}

While the device is programming a page, the controller will idle while

checking the status register as it did during an erase.  During this idle,

both the EREG register and the device status register may be queried.  Once

the status register drops the write in progress line, the top level bit of

the EREG register will be cleared and the interrupt line strobed.  Prior to this

time, any other bus operation will stall the bus until the write completes.

Reads are simple, you just read from the device and the device does everything

you expect.  Reads may be pipelined.  Further, if the device is ever commanded

to read the configuration register, revealing that the quad SPI mode is

enabled, then reads will take place four bits at a time from the bus.

In general, it will take 72 device clocks (at 50~MHz) to read the first word

from memory, and 32 for every pipelined word read thereafter provided that

the reads are in memory order.  Likewise, in quad SPI mode, it will

instead take 28 device clocks to read the first word, and 8 device clocks

to read every word thereafter again provided that the subsequent pipelined

reads are in memory order.

The Quad SPI device provides for a special mode following a read, where the

next read may start immediately in Quad I/O mode following a 12~clock

setup.  This controller leaves the device in this mode following any initial

read.  Therefore, back to back reads as part of separate bus cycles will only

take 20~clocks to read the first word, and 8~clocks per word thereafter.

Other commands, however, such as erasing, writing, reading from the status,

configuration, or ID registers, will take require a 32~device clock operation

before entering.

\section{Low Level}

At a lower level, this core implements the following Quad SPI commands:

\begin{enumerate}

\item FAST\_READ, when a read is requested and Quad mode has not been enabled.

\item QIOR, or quad I/O high performance read mode.  This is the default read

        command when Quad mode has been enabled, and it leaves the device

        in the Quad I/O High Performance Read mode, ready for a faster second

        read command.

\item RDID, or Read identification

\item WREN, or Write Enable, is issued prior to any erase, program, or

                write register (i.e. configuration or status) command.

        This detail is hidden from the user.

\item RDSR, or read status register, is issued any time the user attempts

        to read from the status register.  Further, following an erase or a

        write command, the device is left reading this register over and over

        again until the write completes.

\item RCR, or read configuration, is issued any time a request is made to

        read from the configuration register.  Following such a read, the

        quad I/O may be enabled for the device, if it is enabled in this

        register.

\item WRR, or write registers, is issued upon any write to the status or

        configuration registers.  To separate the two, the last value read

        from the status register is written to the status register when

        writing the configuration register.

\item PP, or page program, is issued to program the device in serial mode

        whenever programming is desired and the quad I/O has not been enabled.

\item QPP, or quad page program, is used to program the device whenever

        a write is requested and quad I/O mode has been enabled.

\item SE, or sector erase, is the only type of erase this core supports.

\item CLSR, or Clear Status Register, is issued any time the last status

        register had the bits {\tt P\_ERR} or {\tt E\_ERR} set and the

        write to the status register attempts to clear one of these.  This

        command is then issued following the WRR command.

\end{enumerate}

\chapter{Registers}\label{chap:regs}

This implementation supports four control registers.  These are the EREG

register, the configuration register, the status register, and the device ID,

as shown and listed in Table.~\ref{tbl:reglist}.

\begin{table}[htbp]

\begin{center}

\begin{reglist}

EREG & 0 & 32 & R/W & An overall control register, providing instant status

        from the device and controlling erase commands.\\\hline

Config & 1 & 8 & R/W & The devices configuration register.\\\hline

Status & 2 & 8 & R/W & The devices status register.\\\hline

ID & 3 & 16 & R & Reads the 16-bit ID from the device.\\\hline

\end{reglist}

\caption{List of Registers}\label{tbl:reglist}

\end{center}\end{table}

\section{EREG Register}

The EREG register was designed to be a replacement for all of the device

registers, leaving all the other registers a part of a lower level access

used only in debugging the device.  This would've been the case, save that

one may need to set bit one of the configuration register to enter high

speed mode.

The bits associated with this register are listed in Tbl.~\ref{tbl:eregbits}.

\begin{table}[htbp]

\begin{center}

\begin{bitlist}

31 & R/W & Write in Progress/Erase.  On a read, this bit will be high if any

        write or erase operation is in progress, zero otherwise.  To erase

        a sector, set this bit to a one.  Otherwise, writes should keep this

        register at zero.\\\hline

30 & R & Dirty bit.  The sector referenced has been written to since it

        was erased.  This bit is meaningless between startup and the first

        erase, but valid afterwards.\\\hline

29 & R & Busy bit.  This bit returns a one any time the lower level Quad

        SPI core is active.  However, to read this register, the lower level

        core must be inactive, so this register should always read zero.

        \\\hline

28 & R/W & Disable write protect.  Set this to a one to disable the write

        protect mode, or to a zero to re--enable write protect on this chip.

        Note that this register is not self--clearing.  Therefore, write

        protection may still be disabled following an erase or a write.

        Clear this manually when you wish to re--enable write protection.

        \\\hline

27 & R & Returns a one if the device is in high speed (4-bit I/O) mode.

        To set the device into high speed mode, set bit~1 of the configuration

        register.\\\hline

20--26 & R & Always return zero.\\\hline

14--19 & R/W & The sector address bits of the last sector erased.  If the

        erase line bit is set while writing this register, these bits

        will be set as well with the sector being erased.\\\hline

0--13 & R & Always return zero.\\\hline

\end{bitlist}

\caption{EREG bit definitions}\label{tbl:eregbits}

\end{center}\end{table}

In general, only three bits and an address are of interest here.

The first bit of interest is bit 27, which will tell you if you are in Quad--I/O

mode.  The device will automatically start up in SPI serial mode.  Upon

reading the configuration register, it will transition to Quad--I/O mode if

the QUAD bit is set.  Likewise, if the bit is written to the configuration

register it will transition to Quad--I/O mode.

While this may seem kind of strange, I have found this setup useful.  It allows

me to debug commands that might work in serial mode but not quad I/O mode,

and it allows me to explicitly switch to Quad I/O mode.  Further, writes to the

configuration register are non--volatile and in some cases permanent.

Therefore, it doesn't make sense that a controller should perform such a write

without first being told to do so.  Therefore, this bit is set upon

noticing that the QUAD bit is set in the configuration register.

The second bit of interest is the write protect disable bit.  Write a '1'

to this bit before any erase or program operation, and a '0' to this bit

otherwise.  This allows you to make sure that accidental bus writes to the

wrong address won't reprogram your flash (which they would do otherwise).

The final bit of interest is the write in progress slash erase bit.  On read,

this bit mirrors the WIP bit in the status register.  It will be a one during

any ongoing erase or programming operation, and clear otherwise.  Further,

to erase a sector, disable the write protect and then set this bit to a one

while simultaneously writing the sector of interest to the device.

The last item of interest in this register is the sector address of interest.

This was placed in bits 14--19 so that any address within the sector

would work.  Thus, to erase a sector, write the sector address, together with

an erase bit, to this register.

\section{Config Register}

The Quad Flash device also has a non--volatile configuration register, as

shown in Tbl.~\ref{tbl:confbits}.  Writes to this register are program events,

which will stall subsequent bus operations until the write in progress bit

of either the status or EREG registers clears.  Note that some bits, once

written, cannot be cleared such as the BPNV bit.

Writes to this register are not truly independent of the status register,

as the Write Registers (WRR) command writes the status register before the

configuration register.  Therefore, the core implements this by writing the

status register with the last value that was read by the core, or zero

if the status register has yet to be read by the core.  Following the

status register write, the new value for the configuration register is

written.

\begin{table}[htbp]\begin{center}

\begin{bitlist}

8--31 & R & Always return zero.\\\hline

6--7 & R & Not used.\\\hline

5 & R/W & TBPROT. Configures the start of block protection.  See device

        documentation for more information.  (Default 0)\\\hline

4 & R/W & Do not use.  (Default 0)\\\hline

3 & R/W & BPNV, configures BP2--0 bits in the status register.  If this bit

        is set to 1, these bits are volatile, if set to '0' (default) the

        bits are non--volatile.  {\em Note that once this bit has been set,

        it cannot be cleared!}\\\hline

2 & R/W & TBPARM.  Configures the parameter sector location.  See device

        documentation for more detailed information.  (Default 0)\\\hline

1 & R/W & QUAD.  Set to '1' to place the device into Quad I/O (4--bit) mode,

        '0' to leave in dual or serial I/O mode.  (This core does not support

        dual I/O mode.)  (Most programmers will set this to '1'.)\\\hline

        otherwise.  (Default 0).\\\hline

        \\\hline

\end{bitlist}

\caption{Configuration bit definitions}\label{tbl:confbits}

\end{center}\end{table}

Further information on this register is available in the device data sheet.

\section{Status Register}

The definitions of the bits in the status register are shown in

Tbl.~\ref{tbl:statbits}.  For operating this core, only the write in progress

bit is relevant.  All other bits should be set to zero.

\begin{table}[htbp]

\begin{center}

\begin{bitlist}

8--31 & R & Always return zero.\\\hline

7 & R/W & Status register write disable.  This setting is irrelevant in the

        current core configuration, since the W\#/ACC line is always kept

        high.\\\hline

6 & R/W & P\_ERR.  The device will set this to a one if a programming error

        has occurred.  Writes with either P\_ERR or E\_ERR cleared will

        clear this bit.\\\hline

5 & R/W & E\_ERR.  The device will set this to a one if an erase error has

        occurred, zero otherwise.  Writes clearing either P\_ERR or E\_ERR

        will clear this bit.

        \\\hline

2--4 & R/W & Block protect bits.  This core assumes these bits are zero.

        See device documentation for other possible settings.\\\hline

1 & R & Write Enable Latch.  This bit is handled internally by the core,

        being set before any program or erase operation and cleared by

        the operation itself.  Therefore, reads should always read this

        line as low.\\\hline

        program operation is in progress.  It will be cleared upon completion.

        \\\hline

\end{bitlist}

\caption{Status bit definitions}\label{tbl:statbits}

\end{center}\end{table}

\section{Device ID}

Reading from the Device ID register causes the core controller to issue

a RDID {\tt 0x9f} command.  The bytes returned are first the manufacture

ID of the part ({\tt 0x01} for this part), followed by the device ID

({\tt 0x0215} for this part), followed by the number of extended bytes that

may be read ({\tt 0x4D} for this part).  This controller provides no means

of reading these extended bytes.  (See Tab.~\ref{tbl:idbits})

\begin{table}[htbp]\begin{center}

\begin{bitlist}

0--31 & R & Always reads {\tt 0x0102154d}.\\\hline

\end{bitlist}

\caption{Read ID bit definitions}\label{tbl:idbits}

\end{center}\end{table}

\chapter{Wishbone Datasheet}\label{chap:wishbone}

Tbl.~\ref{tbl:wishbone} is required by the wishbone specification, and so

it is included here.

\begin{table}[htbp]

\begin{center}

\begin{wishboneds}

Revision level of wishbone & WB B4 spec \\\hline

Type of interface & Slave, (Block) Read/Write \\\hline

Port size & 32--bit \\\hline

Port granulity & 32--bit \\\hline

Maximum Operand Size & 32--bit \\\hline

Data transfer ordering & Little Endian \\\hline

Clock constraints & Must be 100~MHz or slower \\\hline

Signal Names & \begin{tabular}{ll}

                Signal Name & Wishbone Equivalent \\\hline

                {\tt i\_clk\_100mhz} & {\tt CLK\_I} \\

                {\tt i\_wb\_cyc} & {\tt CYC\_I} \\

                {\tt i\_wb\_ctrl\_stb} & {\tt STB\_I} \\

                {\tt i\_wb\_data\_stb} & {\tt STB\_I} \\

                {\tt i\_wb\_we} & {\tt WE\_I} \\

                {\tt i\_wb\_data} & {\tt DAT\_I} \\

                {\tt o\_wb\_ack} & {\tt ACK\_O} \\

                {\tt o\_wb\_stall} & {\tt STALL\_O} \\

                {\tt o\_wb\_data} & {\tt DAT\_O}

                \end{tabular}\\\hline

\end{wishboneds}

\caption{Wishbone Datasheet for the Quad SPI Flash controller}\label{tbl:wishbone}

\end{center}\end{table}

\chapter{Clocks}\label{chap:clocks}

This core is based upon the Basys--3 design.  The Basys--3 development board

contains one external 100~MHz clock.  This clock is divided by two to create

the 50~MHz clock used to drive the device.   According to the data sheet,

it should be possible to run this core at up to 160~MHz, however I have not

tested it at such speeds.  See Table.~\ref{tbl:clocks}.

\begin{table}[htbp]

\begin{center}

\begin{clocklist}

i\_clk\_100mhz & External & 160 & & System clock.\\\hline

\end{clocklist}

\caption{List of Clocks}\label{tbl:clocks}

\end{center}\end{table}

\chapter{I/O Ports}\label{chap:ioports}

There are two interfaces that this device supports: a wishbone interface, and

the interface to the Quad--SPI flash itself.  Both of these have their own

section in the I/O port list.  For the purpose of this table, the wishbone

interface is listed in Tbl.~\ref{tbl:iowishbone}, and the Quad SPI flash

interface is listed in Tbl.~\ref{tbl:ioqspi}.  The two lines that don't really

fit this classification are found in Tbl.~\ref{tbl:ioother}.

\begin{table}[htbp]

\begin{center}

\begin{portlist}

i\_wb\_cyc & 1 & Input & Wishbone bus cycle wire.\\\hline

i\_wb\_data\_stb & 1 & Input & Wishbone strobe, when the access is to the data

                memory.\\\hline

i\_wb\_ctrl\_stb & 1 & Input & Wishbone strobe, for when the access is to

        one of control registers.\\\hline

i\_wb\_we & 1 & Input & Wishbone write enable, indicating a write interaction

                to the bus.\\\hline

i\_wb\_addr & 19 & Input & Wishbone address.  When accessing control registers,

                only the bottom two bits are relevant all other bits are

                ignored.\\\hline

i\_wb\_data & 32 & Input & Wishbone bus data register.\\\hline

o\_wb\_ack & 1 & Output & Return value acknowledging a wishbone write, or

                signifying valid data in the case of a wishbone read request.

                \\\hline

o\_wb\_stall & 1 & Output & Indicates the device is not yet ready for another

                wishbone access, effectively stalling the bus.\\\hline

o\_wb\_data & 32 & Output & Wishbone data bus, returning data values read

                from the interface.\\\hline

\end{portlist}

\caption{Wishbone I/O Ports}\label{tbl:iowishbone}

\end{center}\end{table}

While this core is wishbone compatible, there was one necessary change to

the wishbone interface to make this possible.  That was the split of the

strobe line into two separate lines.  The first strobe line, the data strobe,

is used when the access is to data memory--such as a read or write (program)

access.  The second strobe line, the control strobe, is for reads and writes

to one of the four control registers.  By splitting these strobe lines,

the wishbone interconnect designer may place the control registers in a

separate location of wishbone address space from the flash memory.  It is

an error for both strobe lines to be on at the same time.

With respect to the Quad SPI interface itself, one piece of glue logic

is necessary to tie the Quad SPI flash I/O to the in/out port at the top

level of the device.  Specifically, these two lines must be added somewhere:

\begin{tabbing}

assign {\tt io\_qspi\_dat} = \= (\~{\tt qspi\_mod[1]})?(\{2'b11,1'bz,{\tt qspi\_dat[0]}\}) \hbox{\em // Serial mode} \\

        \> :(({\tt qspi\_bmod[0]})?(4'bzzzz):({\tt qspi\_dat[3:0]}));

                \hbox{\em // Quad mode}

\end{tabbing}

These provide the transition between the input and output ports used by this

core, and the bi--directional inout ports used by the actual part.  Further,

because the two additional lines are defined to be ones during serial I/O

mode, the hold and write protect lines are effectively eliminated in this

design in favor of faster speed I/O (i.e., Quad I/O).

\begin{table}[htbp]

\begin{center}

\begin{portlist}

o\_qspi\_sck & 1 & Output & Serial clock output to the device.  This pin

                will be either inactive, or it will toggle at 50~MHz.\\\hline

o\_qpsi\_cs\_n & 1 & Output & Chip enable, active low.  This will be

                set low at the beginning of any interaction with the chip,

                and will be held low throughout the interaction.\\\hline

o\_qspi\_mod & 2 & Output & Two mode lines for the top level to control

        how the output data lines interact with the device.  See the text

        for how to use these lines.\\\hline

o\_qspi\_dat & 4 & Output & Four output lines, the least of which is the

        old SPI MOSI line.  When selected by the o\_qspi\_mod, this output

        becomes the command for all 4 QSPI I/O lines.\\\hline

i\_qspi\_dat & 4 & Input & The four input lines from the device, of which

        line one, {\tt i\_qspi\_dat[1]}, is the old MISO line.\\\hline

\end{portlist}

\caption{List of Quad--SPI Flash I/O ports}\label{tbl:ioqspi}

\end{center}\end{table}

Finally, the clock line is not specific to the wishbone bus, and the interrupt

line is not specific to any of the above.  These have been separated out here.

\begin{table}[htbp]

\begin{center}

\begin{portlist}

i\_clk\_100mhz & 1 & Input & The 100~MHz clock driving all interactions.\\\hline

o\_interrupt & 1 & Output & An strobed interrupt line indicating the end of

        any erase or write transaction.  This line will be high for exactly

        one clock cycle, indicating that the core is again available for

        commanding.\\\hline

\end{portlist}

\caption{Other I/O Ports}\label{tbl:ioother}

\end{center}\end{table}

% Appendices

% Index

\end{document}