Transcript ppt

Master/Slave Software Architecture
Master
commands and responses are packets not single bytes
void 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);
}
mode is NOT a global variable
Slave
void mainTask() _task_ SL{
manageLoad(mode);
}
COMMANDS
void comTop() _task_ TOP{
read(master,cmd);
write(master,response); //prev
signal(DO);
}// could be ISR
RESPONSES
responses are for
previous command
CSE 466 – Fall 2000 - Introduction - 1
void comBot() _task_ DO {
wait(K_SIG);
response = do(cmd);
// set local mode
}
Sockets are a logical constructs
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.
slave
Master
slave
slave
CSE 466 – Fall 2000 - Introduction - 2
Physical Network
MCU2
Bus
MCU1
Device1
Device2
CSE 466 – Fall 2000 - Introduction - 3
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.
CSE 466 – Fall 2000 - Introduction - 4
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
Application
Application
write(s, buf,n);
read(s, buf,n );
Transport -- TCP
Transport -- TCP
Network -- IP
Network -- IP
Network -- IP
Network -- IP
Datalink -- Ether
Datalink -- Ether
Datalink -- Ether
Datalink -- Ether
fiber
Physical -- Ether
Physical -- Ether
ethernet
fiber
ethernet
CSE 466 – Fall 2000 - Introduction - 5
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)
Application
Application
write(s, buf,n);
read(s, buf,n );
Transport
Transport
Network -- IP
Network -- IP
Network -- IP
Network -- IP
Datalink
Datalink -- Ether
Datalink -- Ether
Datalink
fiber
Physical
Physical
ethernet
fiber
ethernet
CSE 466 – Fall 2000 - Introduction - 6
Example of Physical Layer: SPI Bus
SCK
Master
SCK
SDO
SDI
SDI
void isr() interrupt TIMER {
SDR = S;
while(!SPF);
R = SDR;
}
Slave
SDO
1 0 0 1 1 1 1 0
0
0
0
1
1
0 0
0
shift reg
void isr() interrupt SPF{
R = SDR;
SDR = S
signal(RECV);
}
shift reg
CSE 466 – Fall 2000 - Introduction - 7
Multiple Slave Configuration
SCK
Master
SCK
SDO
SDI
SDI
Slave
SDO
SCK
SDI
SDO
CSE 466 – Fall 2000 - Introduction - 8
Slave
Master Slave Data Link Protocol
 As an example frame is [destination address, command, data]
 An acknowledgement frame is [address, data, checksum]
Master
SCK
SCK
SDO
SDI
SDI
SDO
Slave
mux
SCK
dst
cmd data
dst
type data
SDI
addr data sum type data sum
mux
x
x
x
1
1
1
2
2
2
CSE 466 – Fall 2000 - Introduction - 9
SDO
Slave
Data Link Layer (Master/Slave)
30
end
slave1
ooo
15
cont.
slave1
10
loadtable
slave1
write(slave1, “loadtable 10 15 25 30”); //transport interface
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);
}
}
verify checksum
}
update local DB
with data in the ACK
frame. Handle error.
longer packets =
less overhead but
longer latency (response
time)
not shown:
synchronizing
dealing w/ errors
CSE 466 – Fall 2000 - Introduction - 10
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);
}
}
}
if for me, prepare ACK
assemble into packets and
signal app when packet
complete
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);
}
slave1
loadtable
10
slave1
cont.
15
slave1
end
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);
}
}
CSE 466 – Fall 2000 - Introduction - 11
Trade-off Between Frame Size and Overhead
write(p1, “loadtable 10 15 25 30”); //transport interface
p1
loadtable
10
p1
cont.
15
p1
end
30
Frame: bus is dedicated to that transmission during
the entire frame
or
p1
loadtable
10
15
20
25
30
end
similar to the OS time slice problem: efficiency v. responsiveness
CSE 466 – Fall 2000 - Introduction - 12
Another Physical Layer – I2C
 Multi-mastered
 Send and receive
 Two wire (plus ground)
 Packet oriented (block send)
CSE 466 – Fall 2000 - Introduction - 13
Major Features of I2C
CSE 466 – Fall 2000 - Introduction - 14
Physical Layer
CSE 466 – Fall 2000 - Introduction - 15
Bit Transfer
Transmitter
Master
CSE 466 – Fall 2000 - Introduction - 16
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>
CSE 466 – Fall 2000 - Introduction - 17
An I2C Byte Transfer
MSB First
Rx
MSB……………….LSB
slave
Tx Device
Rx Device
master
CSE 466 – Fall 2000 - Introduction - 18
slave
“Bit Banging” v. Bus Controller
Bit Banging
do all signal transitions in SW
very difficult
IC Interface:
Mem Mapped device:
set your address
initiate transfer
service the device on interrupt
byte received
transmission complete
CSE 466 – Fall 2000 - Introduction - 19
Schematic from App Note
Something is wrong with this picture…but its close
CSE 466 – Fall 2000 - Introduction - 20
Arbitration
what’s the backoff rule?
CSE 466 – Fall 2000 - Introduction - 21
A Complete Frame
MSB……..LSB
CSE 466 – Fall 2000 - Introduction - 22
CSE 466 – Fall 2000 - Introduction - 23