Cypress Semiconductor AN6077 User manual

February 19, 2008 Document No. 001-15342 Rev. ** 1

with FX2LP

Implementing an 8-Bit Asynchronous Interface

Application Note Abstract

This application note discusses how to configure the General Programmable Interface (GPIF) and slave FIFOs of the EZ-USB

FX2LP™ to implement an 8-bit asynchronous interface. The GPIF is a programmable 8 or 16-bit parallel interface that reduces

system costs by providing a glueless interface between the EZ-USB FX2LP and different types of external peripherals. The

GPIF allows the EZ-USB FX2LP to perform local bus mastering to external peripherals implementing a wide variety of protocols.

For example, EIDE/ATAPI, printer parallel port (IEEE P1284), Utopia, and other interfaces are supported using the GPIF block

of the EZ-USB FX2LP. In this example, it masters the slave FIFO interface of another EZ-USB FX2LP.

This implementation uses the GPIF Designer (an utility Cypress provides to create GPIF waveform descriptors) to design the

application specific physical layer. The firmware is based on the Cypress EZ-USB FX2LP firmware ‘frameworks’. A hardware

setup of two back-to-back EZ-USB FX2LP boards is also used, one acting as a master and another as a slave. Familiarity with

the EZ-USB FX2LP development kit, examples and documentation on the development kit CD-ROM, and chapters 9 (EZ-USB

FX2LP Slave FIFOs) and 10 (GPIF) of the EZ-USB FX2LP Technical Reference Manual is assumed.

Introduction

The objective of this application note is to:

■Demonstrate a glueless interface to an 8-bit peripheral

data bus (the FIFO of a slave EZ-USB FX2LP).

■Use EZ-USB FX2LP to transfer data to and from the pe-

ripheral (slave EZ-USB FX2LP) and the USB host.

This application note discusses the necessary hardware con-

nections, internal register settings, and 8051 firmware imple-

mented to execute data transactions over the interface and

across the USB bus.

Figure 1. Hardware Connection Diagram

AN6077

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GPIF Master Pin Descriptions

The GPIF pin names, descriptions, and their uses are dis-

cussed in this section.

RDYn Inputs

RDY[5:0] are ‘ready’ inputs that can be sampled and allow a

transaction to wait (inserting wait states), continue, or repeat

until the signal is at the appropriate level. This implementa-

tion uses RDY0 and RDY1 to control data flow.

RDY0 is tied to FLAGC (EP2 Empty Flag) of the slave and

RDY1 is tied to FLAGB (EP6 Full Flag) of the slave.

Other RDY inputs may be used in the application for addi-

tional debug status information.

CTLx Outputs

CTL[5:0] are programmable control outputs that are used as

strobes, read/write lines, or other outputs.

CTL0, CTL1 and CTL2 are used in this application.

CTL0 is tied to SLRD of the slave.

CTL1 is tied to SLWR of the slave.

CTL2 is tied to PKTEND of the slave.

FD[0:7]

This implementation has an 8-bit data bus. PORTB[0:7]

serves as the data bus on both the master and the slave.

PORTA[6:7]

PA6 and PA7 are tied to FIFOADR0 and FIFOADR1 of the

slave. These are used to drive the address of the FIFO being

accessed by the master.

Slave FIFO Pin Descriptions

The slave FIFO pin names, descriptions, and their uses are

discussed in this section.

SLRD

SLRD is the Slave Read line for the FIFO. SLRD acts as the

read strobe for the slave. CTL0 of the master provides the

strobe.

SLWR

SLWR is the Slave Write line for the FIFO. SLWR acts as the

write strobe for the slave. CTL1 of the master provides the

strobe.

SLOE

In this implementation SLOE is tied to SLRD.

FD[0:7]

This is Port B, which is configured as the 8-bit data bus. If the

WORDWIDE bit of the IFCONFIG register is set, then port D

is configured to be FD[8:15]. This implementation has an 8-bit

interface.

FLAGA/FLAGB/FLAGC/FLAGD

FLAGC is used to indicate the state of ‘emptiness’ of the end-

point 2 FIFO of the slave. FLAGB is used to indicate the state

of ‘fullness’ of the endpoint 6 FIFO of the slave.

FLAGA and FLAGD are not used in this implementation.

FIFOADR[0:1]

The master selects one of the four slave FIFOs using the

FIFOADR pins, and then drives the 8-bit FIFO data using the

SLRD (Slave Read) and SLWR (Slave Write) signals.

PKTEND

PKTEND is used to dispatch a short (less than the maximum

packet size) IN packet to the USB. In this implementation, it is

tied to CTL2 of the master EZ-USB FX2LP.

Creating GPIF Waveforms

This section describes the parameters to create a waveform

and includes figures for graphical clarity. Example code is

also included.

FIFORD

When creating the FIFORD waveform the following timing

parameters must be met.

tRDpwl - SLRD Pulse Width LOW = 50 ns (minimum)

tRDpwh - SLRD Pulse Width HIGH = 50 ns (minimum)

tXFLG - SLRD to FLAGS Output Propagation Delay =

70 ns (maximum)

tXFD - SLRD to FIFO Data Output Propagation Delay =

15 ns (maximum)

tOEon - SLOE Turn on to FIFO Data Valid = 10.5 ns (maxi-

mum)

tOEoff - SLOE Turn off to FIFO Data Hold = 10.5 ns (maxi-

mum)

This results in the following sequence:

s0 Sample the empty flag of the peripheral. If the periph-

eral is ‘not empty’, proceed to s1 else go to s6 where

an interrupt is triggered and the waveform is aborted.

s1 Assert the SLRD strobe and wait for three cycles to

meet the tRDpwl parameter.

s2 Sample the data bus.

s3 Branch to IDLE.

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February 19, 2008 Document No. 001-15342 Rev. ** 3

AN6077

Figure 2 shows the GPIF Designer view of the FIFO Read

waveform.

FIFOWR

When creating the FIFOWR waveform the following timing

parameters must be met.

tWRpwl - SLWR Pulse Width LOW = 50 ns (minimum)

tWRpwh - SLWR Pulse Width HIGH = 50 ns (minimum)

tSFD - SLWR to FIFO DATA Setup Time= 10 ns (mini-

mum)

tFDH - FIFO DATA to SLWR Hold Time = 10 ns (minimum)

tXFD - SLWR to FLAGS Output Propagation Delay =

70 ns (maximum)

This results in the following sequence:

Figure 3 shows the GPIF Designer view of the FIFO Write

waveform. Figure 4 and Figure 5 show the view of the GPIF

waveforms in the gpif.c file. This is the same as is seen in the

GPIF Tool utility.

Figure 2. FIFO Read Waveform in GPIF Designer

Figure 3. FIFO Write Waveform in GPIF Designer

s0 Sample the full flag of the peripheral. If the peripheral

is ‘not full’, proceed to s1, otherwise proceed to s6 to

trigger an interrupt and abort the GPIF waveform.

s1 Assert the SLWR strobe and drive the data bus and

wait for three cycles to meet the tWRpwl parameter.

s2 Deassert the SLWR and increment the FIFO pointer.

s3 Branch to IDLE.

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February 19, 2008 Document No. 001-15342 Rev. ** 4

AN6077

Figure 4. FIFO Read Waveform in gpif.c

Figure 5. FIFO Write Waveform in gpif.c

8051 Firmware Programming (Master)

This section describes how to configure the 8051 to support

the interface on the master side (register settings and others)

and discusses the firmware implemented to perform data

transactions over the local bus and the USB. The complete

code listing is provided at the end of this document.

Firmware Architecture

The firmware is designed to handle USB INs and OUTs arbi-

trarily (for example, the direction of transfer is not favored).

It is also fairly deterministic in its approach and is ‘event-

driven’ by the following key conditions:

OUTs (FIFO Writes)

■Endpoint 2 OUT Has Data

■Peripheral Interface Not Busy (GPIF IDLE)

■Slave Interface FIFO Not Full

INs (FIFO Reads)

■Peripheral Interface Not Busy (GPIF IDLE)

■Slave Interface FIFO Not Empty

■Endpoint 6IN Available Not Full

Since the GPIF is a shared resource between FIFO Reads

and Writes, the peripheral interface status is always checked

before committing the GPIF to launch any form of physical

bus transactions. The firmware is optimized for 512-byte

FIFO Reads and Writes with other mechanisms in place to

handle short packets (1–511 bytes).

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February 19, 2008 Document No. 001-15342 Rev. ** 5

AN6077

The firmware uses the AUTO mode for both IN and OUT

transfers. This means that the maximum size (512 bytes)

packets are committed automatically from the peripheral

domain to the USB domain for OUT transfers. For IN trans-

fers, they are committed from USB to the peripheral domain.

The 8051 is not involved in committing packets. Short pack-

ets are handled by the master strobing the PKTEND of the

slave. In this implementation, the PKTEND of the slave is tied

to CTL2 of the master. So the GPIFIDLECTL register is writ-

ten to strobe PKTEND.

Psuedocode for Master OUT

if GPIF is IDLE

if there is a packet in EP2 OUT

if the peripheral is not FULL

trigger the GPIF Write Transaction

// handle short packet

if the transaction count < 512

if GPIF is IDLE

strobe PKTEND

else

// do nothing; wait for GPIF to be done

else

// do nothing; packet is not short packet

else

// do nothing; peripheral is FULL

else

// do nothing; no data is available to transfer

else

// do nothing; GPIF is not IDLE

Psuedocode for Master IN

if the GPIF is IDLE

if the peripheral is not empty

if EP6 IN is not full

trigger the GPIF Read transaction

if packet is short packet

commit the packet by writing INPKTEND

else

//do nothing; packet is not short

else

//do nothing; EP6 IN is full

else

//do nothing; the peripheral does not have data to transfer

else

//do nothing; GPIF is busy

Expanded Master OUT Code

if( GPIFTRIG & 0x80 )

{

// DONE=1, when GPIF is "idle"

// check if there is a packet in the peripheral domain (EP2OUT)

if( EP24FIFOFLGS & 0x02 )

{

// EF=1 when buffer "empty", for example, no more data to transfer

}

else

{

// EF=0, when slave fifo is "not empty"

// the cpu passed the packet to the peripheral domain (AUTO OUT)

// check if peripheral "not full"

if( GPIFREADYSTAT & 0x02 )

{

// RDY1=1, when peripheral is "not" FULL (tied to peripheral "full" flag)

// drive FIFOADDR lines

OEA = 0xC0;

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February 19, 2008 Document No. 001-15342 Rev. ** 6

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IOA = 0x80;

xFIFOTC_OUT = ( ( EP2FIFOBCH << 8 ) + EP2FIFOBCL );

// setup GPIF transaction count

SYNCDELAY;

EP2GPIFTCH = EP2FIFOBCH;

SYNCDELAY;

EP2GPIFTCL = EP2FIFOBCL;

// trigger FIFO write transaction(s)

SYNCDELAY;

GPIFTRIG = GPIFTRIGWR | GPIF_EP2;

// once master (GPIF) drains OUT packet, it (re)arms to usb domain

// this path is always auto, meaning core handles it

if( xFIFOTC_OUT < enum_pkt_size )

{

// handle short packet to peripheral

// wait for the transaction to terminate naturally

while( !( GPIFTRIG & 0x80 ) )

{

; // poll GPIFTRIG.7, DONE bit

}

// signal short packet to peripheral here

// in this implementation CTL2 is tied to PKTEND of slave strobe PKTEND of slave

GPIFIDLECTL |= 0x04;

GPIFIDLECTL &= 0xFB;

GPIFIDLECTL |= 0x04;

}

else

{

// was max packet size

// let transaction terminate naturally

}

else

{

// RDY1=0, when peripheral is FULL

}

else

{

// DONE=0 when GPIF is "not" IDLE

}

Expanded Master IN Code

// is the GPIF idle

if( GPIFTRIG & 0x80 )

{

// check if peripheral is "not empty"

if( GPIFREADYSTAT & 0x01 )

{

// RDY0=1, when peripheral is "not empty"

// drive FIFOADDR lines

OEA = 0xC0;

IOA = 0x00;

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February 19, 2008 Document No. 001-15342 Rev. ** 7

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if( EP68FIFOFLGS & 0x01 )

{

// EP6FF=1, when fifo "full"

}

else

{

// EP6FF=0, when fifo "not full", for example, buffer available

// setup GPIF transaction count

SYNCDELAY;

EP6GPIFTCH = 0x02;

SYNCDELAY;

EP6GPIFTCL = 0x00;

// trigger FIFO read transaction(s), using SFR

SYNCDELAY;

GPIFTRIG = GPIFTRIGRD | GPIF_EP6;

// wait for transaction to terminate naturally

SYNCDELAY;

while( !( GPIFTRIG & 0x80 ) )

{

; // poll GPIFTRIG.7, DONE bit

}

// AUTOOUT=1, core handles transfers

// cpu is not in the data path however, cpu is responsible for committing "short packets"

xFIFOTC_IN = ( ( EP6FIFOBCH << 8 ) + EP6FIFOBCL );

if( xFIFOTC_IN < enum_pkt_size )

{

// handle short packet from peripheral

SYNCDELAY;

INPKTEND = 0x06;

// w/skip=0;commit however many bytes in packet.

SYNCDELAY;

}

else

{

// core commits packet via EPxAUTOINLENH/L

}

else

{

// master has all the data the peripheral sent

}

else

{

// peripheral interface busy

}

Firmware for the Slave

Since the slave works only in AUTO mode, there is no code

required for data transfer to and from the master, except for

the initialization of registers and specifying the

EP6AUTOINLEN registers.

Summary

This application note describes how to set up the GPIF to

transfer data over an 8-bit asynchronous interface (to the

slave FIFO of another EZ-USB FX2LP). It includes hardware

setup, creating GPIF waveforms, and writing the 8051 code

that arbitrarily handles both USB INs and OUTs.

This application note is centered around a specific back-to-

back board setup with two EZ-USB FX2LP boards. However,

many concepts and insights conveyed in this document can

be applied to and used as a basic framework for mainstream

applications.

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February 19, 2008 Document No. 001-15342 Rev. ** 8

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Code Listing for Master Side

#pragma NOIV // Do not generate interrupt vectors

#include "fx2.h"

#include "fx2regs.h"

#include "fx2sdly.h" // SYNCDELAY macro

extern BOOL GotSUD; // Received setup data flag

extern BOOL Sleep;

extern BOOL Rwuen;

extern BOOL Selfpwr;

BYTE Configuration; // Current configuration

BYTE AlternateSetting; // Alternate settings

// proto's from "gpif.c"

void GpifInit( void );

// 512 for high speed, 64 for full speed

static WORD enum_pkt_size = 0x0000;

// when set firmware running in TD_Poll( ); handles data transfers

BOOL td_poll_handles_transfers = 1;

// when set cpu is out of the data path

BOOL endp_auto_mode_enabled = 1;

//-----------------------------------------------------------------------------

// Task Dispatcher hooks

// The following hooks are called by the task dispatcher.

//-----------------------------------------------------------------------------

void TD_Init( void )

{ // Called once at startup

CPUCS = 0x10; // CLKSPD[1:0]=10, for 48 MHz operation

// CLKOE=0, don't drive CLKOUT

GpifInit( ); // init GPIF engine via GPIFTool output file

// Registers which require a synchronization delay, see section 15.14

// FIFORESET FIFOPINPOLAR

// INPKTEND OUTPKTEND

// EPxBCH:L REVCTL

// GPIFTCB3 GPIFTCB2

// GPIFTCB1 GPIFTCB0

// EPxFIFOPFH:L EPxAUTOINLENH:L

// EPxFIFOCFG EPxGPIFFLGSEL

// PINFLAGSxx EPxFIFOIRQ

// EPxFIFOIE GPIFIRQ

// GPIFIE GPIFADRH:L

// UDMACRCH:L EPxGPIFTRIG

// GPIFTRIG

SYNCDELAY; // see TRM section 15.14

REVCTL = 0x02; // REVCTL.1=1;

SYNCDELAY;

EP2CFG = 0xA0; // BUF[1:0]=00 for 4x buffering

// EP6 512 BULK IN 4x

SYNCDELAY;

EP6CFG = 0xE0; // BUF[1:0]=00 for 4x buffering

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// EP4 and EP8 are not used in this implementation

SYNCDELAY; //

EP4CFG = 0x20; // clear valid bit

SYNCDELAY; //

EP8CFG = 0x60; // clear valid bit

SYNCDELAY; //

FIFORESET = 0x80; // activate NAK-ALL to avoid race conditions

SYNCDELAY; //

FIFORESET = 0x82; // reset, FIFO 2

SYNCDELAY; //

FIFORESET = 0x84; // reset, FIFO 4

SYNCDELAY; //

FIFORESET = 0x86; // reset, FIFO 6

SYNCDELAY; //

FIFORESET = 0x88; // reset, FIFO 8

SYNCDELAY; //

FIFORESET = 0x00; // deactivate NAK-ALL

// 8-bit bus (WORDWIDE=0)

SYNCDELAY;

EP2FIFOCFG = 0x00;

SYNCDELAY;

EP6FIFOCFG = 0x0C;

SYNCDELAY;

EP2BCL = 0x00; // arm first buffer

SYNCDELAY; //

EP2BCL = 0x00; // arm second buffer

SYNCDELAY; //

EP2BCL = 0x00; // arm third buffer

SYNCDELAY; //

EP2BCL = 0x00; // arm fourth buffer

SYNCDELAY;

OUTPKTEND = 0x02;

SYNCDELAY;

OUTPKTEND = 0x02;

SYNCDELAY;

OUTPKTEND = 0x02;

SYNCDELAY;

OUTPKTEND = 0x02;

SYNCDELAY;

SYNCDELAY; //

EP2FIFOCFG = 0x10;

SYNCDELAY;

// IN endp's come up in the cpu/peripheral domain

// setup INT4 as internal source for GPIF interrupts

// using INT4CLR (SFR), automatically enabled

INTSETUP |= 0x03; // Enable INT4 FIFO/GPIF Autovectoring

SYNCDELAY; // used here as "delay"

EXIF &= ~0x40; // just in case one was pending.

SYNCDELAY; // used here as "delay"

GPIFIRQ = 0x02;

SYNCDELAY; //

GPIFIE = 0x02; // Enable GPIFWF interrupt

SYNCDELAY; //

EIE |= 0x04; // Enable INT4 ISR, EIE.2(EIEX4=1)

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}

#define GPIFTRIGWR 0

#define GPIFTRIGRD 4

#define GPIF_EP2 0

#define GPIF_EP4 1

#define GPIF_EP6 2

#define GPIF_EP8 3

void TD_Poll( void )

{ // Called repeatedly while the device is idle

static WORD xFIFOTC_OUT = 0x0000;

static WORD xFIFOTC_IN = 0x0000;

// Registers which require a synchronization delay, see section 15.14

// FIFORESET FIFOPINPOLAR

// INPKTEND OUTPKTEND

// EPxBCH:L REVCTL

// GPIFTCB3 GPIFTCB2

// GPIFTCB1 GPIFTCB0

// EPxFIFOPFH:L EPxAUTOINLENH:L

// EPxFIFOCFG EPxGPIFFLGSEL

// PINFLAGSxx EPxFIFOIRQ

// EPxFIFOIE GPIFIRQ

// GPIFIE GPIFADRH:L

// UDMACRCH:L EPxGPIFTRIG

// GPIFTRIG

OEA = 0xC0;

IOA = 0x80;

if( td_poll_handles_transfers )

{

// Handle OUT data

// is the peripheral interface idle

if( GPIFTRIG & 0x80 )

{

// DONE=1, when GPIF is "idle"

// check if there is a packet in the peripheral domain (EP2OUT)

if( EP24FIFOFLGS & 0x02 )

{

// EF=1 when buffer "empty", for example, no more data to transfer

}

else

{

// EF=0, when slave fifo is "not empty"

// the cpu passed the packet to the peripheral domain (AUTO OUT)

// check if peripheral "not full"

if( GPIFREADYSTAT & 0x02 )

{

// RDY1=1, when peripheral is "not" FULL (tied to peripheral "full" flag)

// drive FIFOADDR lines

OEA = 0xC0;

IOA = 0x80;

xFIFOTC_OUT = ( ( EP2FIFOBCH << 8 ) + EP2FIFOBCL );

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