ARINC 429 with a Host Processor on an FPGA

ARINC 429 with a Host Processor on an FPGA

2005 MAPLD International Conference

September 2005

Paper #236

Ian Land

Ryan Mohan

MAPLD 2005/236Land 2

Introduction

Trends Technological advances in semiconductor size and speed,

coupled with the demand for custom logic, has led to the use of FPGAs to implement several systems on one chip.

Electronic Bus Systems ARINC 429, MIL-STD-1553 and Ethernet-MAC are used in

systems with data link layer controller and host processor (uP) ARINC 429, a low-speed standard, requires no more than an 8-

bit host processor

An FPGA with integrated Data Link Controller and Host There are many considerations to be made when interfacing an

ARINC 429 bus Interface to a host processor, including Glue logic Application code


ARINC 429 Overview ARINC 429 Standard

ARINC 429 is a two-wire, point-to-point data bus that is application-specific for commercial and transport aircraft.

Words are 32 bits in length and are transmitted at either 12.5 or 100 kbps to other system elements monitoring the 429 bus.

ARINC 429 uses a unidirectional data bus standard - the Mark33 Digital Information Transfer System with Tx & Rx on separate ports

Actel ARINC 429 Provides a complete Transmitter (TX) and Receiver (RX) solution for up

to 16 Tx and 16 Rx channels per the ARINC 429-16 specification Each channel has selectable data rate and label memory size

Selectable system clock Programmable interrupt and FIFO generation Internal wrap-around testing Requires external (standard) ARINC 429 line drivers and line receivers

to interface to the ARINC 429 bus. An external host CPU is necessary to set up the core’s control

registers and initialize the label memory. Consists of three main blocks: Transmit, Receive, and CPU Interface.


ARINC 429 IP CoreBus Interface – a 32-Bit Data Word

32nd Bit is the parity bit SSM is the Sign/Status Matrix ARINC Data formats are commonly encoded as Binary Data

(BNR) and Binary Coded Decimal (BCD) SDI, the Source Destination Identifier,

specifies the intended receiver The lower 8 Bits specify label word

Varies depending on the particular equipment and systems that require interconnection


ARINC 429 IP Core CPU Interface - direct CPU access to memory

The Internal Registers can be read/written via a 9-Bit CPU address

Channel Number can range from 0 to 15 Tx/Rx Bit specifies whether a Tx or Rx register is being addressed Register Index specifies which Core429 internal register is being

addressed:RX Registers: 0 – Data Register TX Registers: 0 – Data Register

1 – Control Register 1 – Control Register

2 – Status Register 2 – Status Register

3 – Label Memory 3 – Unused

Byte Index is used to control CPU read/writes depending on the CPU datapath width (4 operations for 8-bit CPU, 2 for a 16-bit CPU, 1 for a 32-Bit CPU)

Easily interfaced to the Actel 8-bit 8051 uP


8051 8-Bit Processor IP Core

Overview High performance, single-chip, 8-bit

microcontroller.

Features Some of the key features are:

32-Bit I/O Ports Serial Port Two 16-Bit Timer/Counters Interrupt Controller – Four Priority

Levels with 13 Interrupt Sources Internal Data Memory Interface External Memory Interface Optional On-Chip Instrumentation

Debug Logic Optional Power-Saving Modes


8051 Processor IP Core Internal Special Function Registers (SFRs) hold data and

control the timer, interrupts and serial ports

Four separate memory regions accessible to the CPU DATA

256 bytes of memory used for dynamic storage of program data such as register, stack, and variable data. Typically, only the lower 128 bytes are directly addressable for program data. Addressing the upper 128 bytes points to the SFR memory region.

CODE 64 KB of memory used for program storage and interrupt vectors.

XDATA 64 KB of memory used for storage of large data sets, custom-

designed peripherals, and extended stack space if necessary.

SFR Upper 128 bytes of DATA space is a combination of internal core

memory and external memory used for internal and external SFRs.


ARINC 429 IP Interfaced to 8051 uP

System overview 8051 IP is host CPU for ARINC 429 Bus Interface IP

Implemented on one FPGA and integrated alongside other Intellectual Property to create a single chip solution.

Depends on the existence of easy to use interface logic The 8051 SFR Interface The 429 CPU Interface


429 Interfaced to a 8051 uP

Interface Logic – 8051 SFR Interface Can service up to 101 External SFRs External SFRs can be used to interface with an off-core

peripheral, such as an ARINC 429 Bus Interface Core. Such a peripheral can use all addresses from the SFR address

space range 0x80 to 0xFF except those already implemented within Core8051 as Internal SFRs. Although the SFR address space contains 8-bit addresses, the

external SFRs are addressed by a 7-bit address which corresponds to the 8-bit internal address with the MSB removed.

External Special Function Register Interface



Interface Logic – 8051 SFR Interface Due to the restricted memory map, an indirect addressing

capability was created Use memory-mapped registers (external SFRs) to hold the Core429 9-

Bit CPU address and the corresponding data.

This 429-to-8051 system implements 4 external SFRs The 9-Bit CPU address requires two of the 8-Bit SFRs

Leaves one SFR with 7 unused bits, providing a convenient means for control/handshaking functions.

One SFR is used for data written to the 429 Bus Interface IP from the 8051 Host and one SFR for data read by the Host 8051



Interface Logic - ARINC 429 IP CPU Interface Allows the system CPU (8051 IP) to:

Read/Write ARINC data to the ARINC 429 IP internal FIFO Access the 429 control and status registers Write to the 429 internal label memory

This system requires that the 429 IP be configured with a CPU_DATA_WIDTH of 8 Bits to interface to the 8-Bit 8051 CPU



Interface Logic – Glue Logic Advantage: Only a small amount of glue logic is needed to integrate

the IP Cores if the 8051 and the ARINC 429 cores are in the same clock domain This system (with 4 TX and 4 RX channels) is physically implemented

on an Actel Development Board where both cores operate off a common 16 MHz clock.

CPU I/F



Interface Logic – Glue Logic Physically connects 429 IP to 8051 IP Host Enforces a communication protocol between the two cores

In this Core429-Core8051 System, the 4 SFRs used (0x40, 0x41, 0x42, 0x43) are mapped to WRITE_ADDRESS0, WRITE_ADDRESS1, WRITE_DATA, READ_DATA respectively


429 Interfaced to a 8051 uP Interface Logic – Glue Logic

Implementation Decodes the sfraddr input from the 8051 Host by comparing against

the predefined memory-map Controls the handshaking between the 8051 Host and 429 IP Accumulates the 9-Bit CPU address from the 2 address SFRs and

sends it to Core429 Passes data between Core8051 and Core429 according to the

protocol discussed The verilog implementation of this logic is available for viewing

8051 Application Code The system is able to execute user programs written in C and

cross-compiled into 8051 assembly code Application code that uses ARINC 429 functions must follow the

communication protocol discussed Sample application code is available for viewing


Verification Verified cores individually

Against datasheet and ARINC standard 100% Code Coverage target

Simulated the system Verify the interface between the cores HW/SW co-verification could help verification of ARINC data transfers

Takes a substantial effort and long simulation run times

Tested the hardware Efficient method was to program the FPGA and run the software Found no handshake between 8051 and ARINC 429 bus interface

Reviewed the design after unsuccessful handshake Reviewed logic analyzer data, focused on 8051 SFR interface Changed communication protocol, re-designed glue-logic and changed

application code Handshake occurred


Verification (p2)

Application software tests Core429 to host CPU Early SW – write & read ARINC 429 data to individual registers Interface through RS-232 and hyper terminal on a PC More sophisticated software after handshake

Loopback test and communication with 4 TX / 4 RX channels

Once the handshake worked1. Internal FPGA loop back test

2. Verify off-chip, but within the development platform Send signal from daughter card’s transmit to receive connections

3. Connect to ARINC 429 tester to debug, verify and validate With FPGA, we checked different ARINC 429 configurations

(loopback, etc.)


Verification (p3)

Test against standard System vs. ARINC 429 data monitor

TX- SW terminal interface via RS-232 to host CPU, which instructed Core429 to send data to the tester via transmit channels

RX – Tester sent ARINC data word to the bus which was received by FPGA where we monitored RX FIFO with terminal


429 IP Core Interfaced to a M68K System Overview

A small amount of glue logic is needed to connect the 429 CPU Interface to the M68K address and data buses


429 IP Core Interfaced to a M68K Several considerations for interfacing

Match Clocks - ie. 20 MHz Match CPU_DATA_WIDTH on Core429 to 16-bit M68K data bus width Consider how the 429 Internal Registers and Memory are addressed

and accessed Directly mapping the 429 9-bit address to the relatively large M68K address

bus is an effective solution Requires that a 9-Bit address space in the M68K memory map be reserved

for communication with the 429 Bus Interface IP For example, 0x00000000-0x000001FF, could be reserved unless this address

space is pre-reserved by the M68K or another device Note that there can be up to 8 TX and 8 RX ARINC 429 channels implemented

while the MSB of the 9-Bit 429 CPU address will remain zero

CPU Interface The 429 CPU Interface would perform the same function as in the 429-

8051 system Based on the variation of M68K used, the width of the cpu_dout and cpu_din

signals will be have to be adjusted accordingly


429 IP Core Interfaced to a M68K Interface Logic – Glue Logic Block Diagram

The glue logic block interfaces the 429 CPU Interface to the M68K address and data bus. This block is required to follow a communication protocol that adheres

to the M68K bus communication protocol


429 IP Core Interfaced to a M68K Interface Logic – Glue Logic

One possible communication protocol is shown below

Note: The above description is for a 16-Bit read/write. 32-Bit ARINC 429 data operations require two read/write operations with the appropriate CPU address and data. During 8-Bit operations (on the 429 control/status registers, and label memory) only one of either UDS or LDS will be asserted at a time.


429 IP Core Interfaced to a M68K

Interface Logic – Glue Logic/Application Code Another important consideration for an ARINC 429-to-Host

CPU system is its application Many applications are better implemented by using interrupts

to indicate to the CPU that an ARINC 429 event has occurred The 429-8051 system is part of a terminal interface that

continually waits for user commands, via a keyboard Thus the register polling approach is acceptable

Most applications favor the use of interrupts over the register polling approach used in the 429-8051 system Interrupts will free up the host CPU to perform other operations

and functions

To completely specify the glue logic between the 429-to-M68K system, the interrupt lines IPL0, IPL1, and IPL2 need to be interfaced with the 429 Bus Interface IP Core

If interrupts are used, the M68K assembly code used for 429 operations would reside in an Interrupt Subroutine (ISR)


Lessons Learned Integrating cores is not a simple connect

Multiple Clock Domains Single clock domain is the simplest, fastest and safest

Address and Data Bus Widths How much address space does the core require relative to that available ? Does the core have the same data bus width as the processor ?

What about performance At what rate does the processor need to access the core

Does it require direct access Is slow polled access possible

Application code must match the system and protocol

System simulation is required You should always run system-based simulations

It is quicker and better than trying to debug the FPGA in hardware Can try more configurations than on board (loopback, 4/4, 16/16)

Customers and local FAEs also verified 4/5, 4/8 and many other variations

A design is not ‘integrated’ until it is hardware tested Core429/Core8051 would not communicate in HW

Additional debugging of IP and application SW code for handshake Core429/68K is likely to need debugging, too.

ARINC 429 with a Host Processor on an FPGA

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