Slide 1

worstell@copper.net

Robust Low-Power MSP430 Networking with aBuffer Insertion Ring

Glen Worstell

Sugle Consulting

worstell@copper.net

More info:

www.worstell.com

Slide 2

worstell@copper.netAgenda

• Application areas for small networks

• Common small network solutions

• The “Buffer Insertion Ring” network Protocol MSP430 Hardware MSP430 Software

• Comparison of BIR with other solutions

• Description of BIR demonstration code

• Q&A

Slide 3

worstell@copper.netSmall network applications

• Auto and other vehicle data & control LIN commonly used

• Industrial process control

• Lab data collection

• Home automation

• Medical data collection

• HVAC

Slide 4

worstell@copper.netCommon Micro Networks

• CAN Multi-Master 1Mbps 8 Byte Messages

• LIN Master-Slave (sort of) 20K bps 8 Byte Messages

• BIR Multi-Master 50K bps 8 Byte Messages

• Home-grown RS-485

Slide 5

worstell@copper.netWhy BIR?

Extremely low idle power Isolated (with isolated power supply) Lowest cost, esp. in small quantities Uses available hardware (UART) Low EMI generation Low EMI susceptibility Multi-master Can use with other micros (but not low power)

Slide 6

worstell@copper.netWhy not BIR?

• Can’t disable interrupts for very long But could use 2nd MSP430

• Requires Xtal But could use LIN-like scheme

• 1 Byte latency per node About 1 Msec per node at 10K baud

Slide 7

worstell@copper.netBIR Concept

• Unique node numbers

• Node sends message (to all other nodes) whenever necessary

• Asynchronous serial node transceivers Built-in UART Bit-Bang (F1121)

• 4-Wire Cable (RJ-11?) Power, Ground Balanced pair BIR data 2 to 32 nodes

• Optical Isolators

Slide 8

worstell@copper.netBIR message format

Slide 9

worstell@copper.netTransceiver Hardware

Slide 10

worstell@copper.net9-bits/byte Message Format

• Address Byte Node Number of Sender (5 bits) Number of Data Bytes (2 bits) Parity (1 bit)

• Data Byte (8 bits)

• Extra Data Bytes (8 bits each)

• Checksum (8 bits, like LIN or CRC-8)

Slide 11

worstell@copper.netNumber of Data Bytes Coding

• 0: One Data Byte

• 1: Two Data Bytes

• 2: Four Data Bytes

• 3: Eight Data Bytes

Slide 12

worstell@copper.netInsertion Buffer Idea

• Each node has a buffer

• Incoming data goes in buffer

• To Send: If buffer is empty, put message into buffer Otherwise, wait until it is empty

• Messages from other nodes are passed on

• Messages from this node are not passed

• A note about baud rate divisors If small n, n should be odd

Slide 13

worstell@copper.netBIR software flowchart

Slide 14

worstell@copper.netThe Three-node Demo

• Each node sends to a random other node

• Sending occurs at random intervals

• Random message:” turn on LED” or “turn off LED”

• Stop blinking for one minute if any error is detected

• Source code on web

• Uses simple RTOS and “Random” number generator

Slide 15

worstell@copper.netDemo photo

• BIR demo - 2 HW UART, 1 Timer-A UART

Slide 16

worstell@copper.netAn RTOS for limited RAM

• Single Stack

• Cooperative

• Standard C

• See “Salvo” for similar scheme

• Source code on web www.worstell.com

Slide 17

worstell@copper.netBasic RTOS idea

• Suspend only from Main()

• Nothing is on the stack

• Need to save only the return address

• See “ProtoThreads”, Adam Dunkels, www.sics.se/~adam/pt/

Slide 18

worstell@copper.net

A good PRNG without hardware multiply• Poor PRNGs are very common

Feedback shift registers arithmetic modulo a power-of-2

• “Random Number Generators - Good Ones are Hard to Find” Park ,SK & KW Miller, CACM, Oct. 1998 X(n+1) = (A*X(n)+B) mod M

• Multiplicative, Congruential Random-Number Generators with Multiplier +- 2^K1 +- 2^K2 and Modulus 2^P - 1, Pei Chi Wu, ACM Trans. On Mathematical Software, June 1977

Slide 19

worstell@copper.netQ&A

• Email: worstell@copper.net

• More info, source code: www.worstell.com