cse 466 – fall 2000 - introduction - 1 commands responses master/slave software architecture...

$: CSE 466 – Fall 2000 - Introduction - 1 COMMANDS RESPONSES Master/Slave Software Architecture Master void master() _task_ MAST{ Button(mode); // enq(cmd)$
CSE 466 – Fall 2000 - Introduction - 1

COMMANDS

RESPONSES

Master/Slave Software Architecture

Mastervoid master() _task_ MAST{ Button(mode); // enq(cmd) checkDB(mode); // enq(cmd)}void comTop() _task_ COM{ wait(K_TMO, 1); if (!deq(cmd)) { cmd = pollCmd(next++); slave = next; } else slave = toWho(cmd); write(slave, cmd); read(response); signal(VERIFY);} void comBot() _task_ VERIFY{ // match up resp. and commds wait(K_SIG); verify(response); updateDB(response);}

Slavevoid mainTask() _task_ SL{ manageLoad(mode);}

void comTop() _task_ TOP{ read(master,cmd); write(master,response); //prev signal(DO);}// could be ISR

void comBot() _task_ DO { wait(K_SIG); response = do(cmd); // set local mode}

commands and responses are packets not single bytes

responses are forprevious command

mode is NOT a global variable


Sockets are a logical constructs

Master

slave

slave

slave

socket == 2-way fifo

Socket could be implemented in shared memory, internet, or anything in between.

High level architecture can be independent of implementation choices.


Physical Network

MCU1

MCU2

Device1

Device2

Bus


ISO Network Layers – modularity/interop.

Physical Layer: What physically moves a bit/byte from one place to another (ethernet). Devices have a local physical address. Voltage Current Photons Radio Sonar

Data Link Layer: Guarantees delivery of “frames” over the physical layer, to the physical address. Assembles/dissembles packets from/to frames. Address (Source and Destination) Checksum Data Usually a fixed size or maximum size.

Network Layer: Primarily responsible for routing of network packets Maps packet destination address from/to local physical address Adds network layer header to packet Gives packets w/ header to data link layer, along with physical address.


ISO Layers Continued Transport Layer: responsible for end-to-end protocol of user data buffer transmissions.

Source and destination addresses are private – host to host. Maps application space channel (socket) name to network address. makes network packets w/ transport header and communicates w/ network layer.

Each layer has a peer-to-peer and an intra-stack protocol

Transport -- TCP

Network -- IP

Datalink -- Ether

Physical -- Ether ethernet fiber

Datalink -- Ether

Network -- IP

fiber ethernet

Datalink -- Ether

Network -- IP

Transport -- TCP

Network -- IP

Datalink -- Ether

Physical -- Ether

write(s, buf,n); read(s, buf,n );

Application Application


Transport

Network -- IP Network -- IP

Transport

Network -- IP Network -- IP

Embedded Networking: Simplest Case Simple case: socket name is the same as physical address. No mapping, we just need

to break our message into frames…maybe

Physical Layer – typically low bandwidth, serial, byte oriented

Data link layer – read/write interface to the application

frames: destination address, data, checksum. No mapping from sockets to network address No mapping from network address to physical address (no routing)

Datalink

Physical ethernet fiber

Datalink -- Ether

fiber ethernet

Datalink -- Ether Datalink

Physical

write(s, buf,n); read(s, buf,n );

Application Application


Example of Physical Layer: SPI Bus

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

void isr() interrupt TIMER { SDR = S; while(!SPF); R = SDR;}

void isr() interrupt SPF{ R = SDR; SDR = S signal(RECV);}

1 0 0 1 1 1 1 0

shift reg

0 0 0 1 1 0 0 0

shift reg


Multiple Slave Configuration

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

Slave

SCK

SDI

SDO


Master Slave Data Link Protocol

As an example frame is [destination address, command, data]

An acknowledgement frame is [address, data, checksum]

Master Slave

SCK

SDO

SDI

SCK

SDI

SDO

Slave

SCK

SDI

SDO

mux

dst cmd data dst type data

addr data sum type data sum

mux x x x 1 1 1 2 2 2


Data Link Layer (Master/Slave)

void physical() interrupt TIMER { S = deq() setMux(S); SDR = S while (!SDF); R = SDR; signal(DLIN);}void datalink() _task_ DLIN { while(1) { wait(); frame[i++] = R; if (i == 3) { i = 0; process(frame); } }}

void physical() interrupt SF { R = SDR; SDR = deq(); signal(DLIN);}void datalink _task_ DLIN { while (1) { wait(); frame[i++] = R; if (i == 3) { i = 0; process(frame); } }}

longer packets =less overhead but longer latency (responsetime)

loadtable slave110cont. slave115end slave130 o o o

write(slave1, “loadtable 10 15 25 30”); //transport interface

verify checksumupdate local DBwith data in the ACKframe. Handle error.

if for me, prepare ACKassemble into packets andsignal app when packetcomplete

not shown: synchronizingdealing w/ errors


Application Interface to Data Link Layer

void mast() _task_ app { … // application layer protocol defines meaning write(SLAVE1, “loadtable 10 15 20 25 30”); //blocking …}void write(int dst, char *command{ // transport interface frame_array = mkFrames(dst,command); for (each byte in frame array) enq(byte);}

loadtableslave1 10

cont.slave1 15

endslave1 30

void slave()_task_ app( while(1) { if (!read(master, cmd)) do(cmd); other_processing() }}int read() { if (test(READ)) { sprintf(cmd,”%s”,deq()) return(0); } return(-1)}void process(char *frame) { response = resp(frame); for (each byte) enq(response); if (addframe(p,frame)) { enq(p); p = new packet(); signal(READ); } }


Trade-off Between Frame Size and Overhead

write(p1, “loadtable 10 15 25 30”); //transport interface

loadtablep1 10

cont.p1 15

endp1 30

or

loadtablep1 10 15 20 25 30 end

Frame: bus is dedicated to that transmission duringthe entire frame

similar to the OS time slice problem: efficiency v. responsiveness


Another Physical Layer – I2C

Multi-mastered

Send and receive

Two wire (plus ground)

Packet oriented (block send)


Major Features of I2C


Physical Layer


Bit Transfer

Transmitter

Master


Who gets to be master

The one who initiates a frame:

A frame is:<Start><addr><data>…<data><Stop> OR<Start><addr><data>…<data><R_Start><addr><data>…<Stop>


An I2C Byte Transfer

Tx Device Rx Device

master

slave slave

Rx

MSB First

MSB……………….LSB


“Bit Banging” v. Bus Controller

Bit Bangingdo all signal transitions in SWvery difficult

IC Interface:Mem Mapped device:

set your addressinitiate transferservice the device on interrupt

byte receivedtransmission complete


Schematic from App Note

Something is wrong with this picture…but its close


Arbitration

what’s the backoff rule?


A Complete Frame

MSB……..LSB

cse 466 – fall 2000 - introduction - 1 commands responses master/slave software architecture...

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