Recap

1
Recap
Covered in Detail
Covered with a few things missing
2
BitWise I/O

• Toggling individual bits can be cumbersome
• Write only registers require local copy
• Processor must AND, OR to avoid other bits
• Parallel Port D,E bits can be individually
  addressed in sep. registers
• PEB7R, PEB6Retc
• Write to the corresponding register changes that
  bit only

3
Output Synchronization

• As mentioned in class earlier
• Parallel Ports DEFG
• Data register is written to ahead of time but
  will actually change on
• PCLK/2, (default) or
• Timer_A1
• Timer_B1
• Timer_B2

Ref Creating Precisely Timed Output Pulses
(R3000 UM 4.1)
4
Communicating With the Outside World

• Serial Communication Standards and Peripherals in
  Microprocessors

5
Why Serial I/O?
Lots of Parallel I/O I/O pin limitations Tend
to be higher power Long Cables required for
externals PCB Routing cumbersome Serial I/O can
actually be faster, because cross-talk issues
can beeliminated.
R3000
A/D
D/A
Processor 2

covered
6
Serial Communication

• Time Domain Multiplexing of Multiple Bits of Data

Example to send a xD3 from one device to another
Synchronous A shared clock is used to
precisely determine when a bit-time has
elapsed. Asynchronous The data contains
symbols which aid in synchronization, and the
devices need not have precisely the same bit
clock
This is just a general principle, there are
billions of ways to take advantage of these
general principles. We need standards for device
interoperability
covered
7
Some Examples of Serial Communication Standards

• UART
• SPI / Microwire
• I2C
• IrDA
• TV Remote Controls
• HDLC
• Bluetooth The name Bluetooth was born from the
  10th century king of Denmark, King Harald
  Bluetooth (whose surname is sometimes written as
  Bluetooh), who engaged in diplomacy which led
  warring parties to negotiate with each other. The
  name of the king in Danish was Harald Blåtand and
  the Bluetooth logo is based on the H and B runes.
  
• Ethernet
• USB
• CAN (Controller Area Network, prevalent on
  automobiles)
• Semi-Custom

covered
8
Serial Bus Terms

• Full Duplex data can be sent an received
  simulataneously (Ant Half Duplex)
• Master / Slave One device is master and others
  are slaves.
• Multi-Master Bus may have more than one master,
  arbitration scheme necessary
• Peer-Peer No master, everyone is equal.
• Multi-Point Several transceivers on same set of
  wires.

covered
9
Motivation ADS7818 Operation Modes
10
DSK Codec McBSP Configuration

• When communicating with the on-board codec, the
  DSP acts as a slave, that is, all control signals
  come from the codec itself
• The bit clock SCLK (CLKX, CLKR) and the framesync
  FS (FSX, FSR) is externally driven and active
  high
• The McBSP should begin sampling 1 clock after FS
  signal is detected
• Data should be sampled on the falling edge of
  SCLK (CLKR) and transmitted on the rising edge of
  SCLK (CLKX)
• Data is 16 bits long, with the MSB first

11
PCM3006 and McBSP
32clks, viewed as a single DSP word
SYSCLK
12.288 MHz (on codec board)
12.288 MHz/256 48kHz fs LRCIN
When communicating with the PCM3006, the DSP
takes the external clock and produces all of the
control signals.
12
RS-232

• This ubiquitous standard actually define voltage
  levels and pin connections, but not protocol
  i.e., this standard does not define character
  encoding, character framing (bits per character,
  start/stop bits, etc.)
• Generally used with a particular set of
  asynchronous signaling standards.

Computer
Voltage gt 3V 0, lt -3V 1 (Use a converter
IC to get these levels)
RS232 Signals and pinouts
13
Universal Asynchronous Protocol
Note! This diagram neglects the inversion
specified by 232 std!
LSB First!
Bitclk baud rate

• There are two types of parity bits even parity
  bit and odd parity bit.
• Even parity bit is set to 1 if number of ones in
  given set of bits is odd (making the number of
  ones even).
• Odd parity bit is set to 1 if number of ones in
  given set of bits is even (making the number of
  ones odd).
• Protocol Variants specified by Data Bits, Parity
  Bit, Stop Bits, (and Baudrate)
• 8-Odd-1
• Popular Variants
• 8-None-1, 7-E-1

This type of serial standard is useful for
talking to a wide variety of COTS devices GPS
receivers, sensors, other microprocessors, and
your PC. Benefits Simplicity
14
UART

• Universal Asynchronous Receiver Transmitter.
• Most PCs have one
• Implements this set of asynchronous protocols in
  hardware
• Configure it ahead of time for the right bit
  timing and protocol, and simple readswrites
  perform serial Comms.

15
I2C

• Inter-Integrated Circuit bus (I2C). Patented by
  Phillips Semiconductors.
• Half Duplex, Synchronous, Multi-Master
• 2 signal lines SDA, SCL
• Uses open drain drivers (contention will never
  cause damage)
• Speeds 100kbps, 400kbps, 3.4Mbps
• Typically on-board, or very short cable

16
2-Wire -- like I2C
many variants of I2C like interface that arent
exactly I2C.BitBanged on rabbit, but functions
are available, other processors have in HW
17
Other Synchronous Protocols
Case study -- AD9874 IF Downconverter / Digitizer
Contains 2 Serial Interfaces 1) SPI (serial
peripheral interface) port for configuration
setting frequencies, reporting status (slow
stuff) 2) Synchronous Serial Interface SSI
For fast streaming of digitized data
18
SPI
Motorola developed SPI (Serial Peripheral
Interface) protocol Signals MOSI, MISO, SCK,
/CS. Up to 1Mbps, but often bit-banged
Synchronous Serial Interface SSI For fast
streaming of digitized data
19
R3000 Serial Ports (USART)

• 6 Serial Ports A F
• All Asynchronous Mode w/ baud rate lt 1/8 the
  system clock rate
• A-D Clocked Serial Mode Synchronous
• R3000 can provide clock clk rate lt ½ system
  clock rate
• R3000 can use clock provided by external device.
  Clk rate lt 1/6 system clock rate
• A Processor can be booted from this serial port
  after reset.
• Mode pins set, data is loaded in triples (addrl,
  addrh, data)

20
Baudrate Generation

• Each serial port has an associated timer which is
  used to generate the bit clk
• That timer isnt available for other things
• Clock input to serial port 8xbaudrate in async
  mode (2x for sync, internal)

21
R3000 Protoboard
22
Standard Asynchronous Transmit

• After configuration, operation is quite simple
• Writes to SxDR take data from processor, place it
  in SxDR
• If shift register is available, data is taken
  from the SxDR and placed into the shift register,
  where it is shifted out serially
• Interrupts Serial Port generates an interrupt
  when
• SxDR is available to write again
• Enables continuous communication
• Shift Register becomes IDLE
• So you know when all data has actually been sent
  out

23
Standard Asynchronous Receive

• Data is shifted into the Receive Shift Register
• When complete Data is transferred to the SxDR
• Note that reading this reg gives contents of
  receive register, writing writes to xmit register
• Interrupt generated when new data arrives to the
  receive data register.

24
Using the Serial Ports

• Setup the appropriate clock source for the
  associated timers (A2-A7) by setting the Timer A
  Control Register (TACR)
• Set the chosen bit rate by loading the
  appropriate timer constant register (TATxR) with
  the divisor
• Enable the appropriate pins on the output ports,
  since GPIO and the serial ports share I/O pins
• The appropriate Serial Port Control Register
  (SxCR) must be set up to selec the serial mode
  (async, sync, external clked), the number of data
  bits, and the interrupt priority
• If interrupts are to be used, the must be
  declared and attached

25
Sending a single character
WrPortI(SBDR,NULL,5)
Writes a 0x35 to the SBDR
Output 5
or
Ioi ld (SBDR),a
Writes the character in the accum to the serial
port
26
Example
void main() configure serial ports asm ld
a,0x35 ioi ld (SBDR),a ld a,0x36 ioi ld
(SBDR),a ld a,0x37 ioi ld (SBDR),a endasm
What gets printed to our serial terminal?
27
Dynamic C Serial Port Support

• Functions provided in Dynamic C handle a lot of
  the tedium for simple communication (RS232.lib)
• serXopen (19200)
• Sets up the serial port for the baudrate desired
• Creates its own interrupt and buffers for
  handling the data as it arrives, and sending it
  as available
• define XINBUFSIZE 15
• define XOUTBUFSIZE 15
• Data will fill these buffers as it is received,
  and you may access it through the other functions
  provided
• Data you write using the functions will fill
  these buffers, and will be automatically
  transferred to the serial port as it is ready

28
DC Serial Xmit Functions

• serXwrite(void data, int length)
• serBwrite(myarray, 10)
• serXwrfree()
• // returns an int of free bytes in the transmit
  buf
• serXwrFlush() // flushes buffer (doesnt send)
• serXputs() // calls serXwrite(s,strlen(s))
• serXputc(d) //writes a single character
• serXclose() //closes the port, disconnects irq

29
DC Serial Read Functions

• serXgetc() // returns int with next avail
  character
• serXpeek() // returns int with next avail
  character but doesnt remove it from buf
• serXrdFlush()
• serXrdFree() // returns int with free space
• serXrdUsed() // returns int
• serXread(data_ptr, length,timeout)
• Reads length bytes into data_ptr or until timeout
  value expires between bytes

30
R3000 serial ports

• HW support for UART signalling
• SPI, Other straightforward synchronous Interfaces
• SPI is common enough that it is supported through
  the BIOS as well, SPIinit(), SPIwrite(),
  SPIread(), SPIWrRd()
• SW support for I2C
• HDLC
• Very popular?
• IrDA
• Comms with PDAs, Cell Phones..etc.

31
Serial Port Exam Question

• Serial Ports
•  
• 5) Your R3000 based system has several interfaces
  to the outside world, one of which is a serial
  connection to a UART based serial port on a
  standard PC.  The baudrate you choose for
  communication is 10kbaud.  (note this is just to
  make the calculations easy in case you dont have
  a calculator.  You wont actually find this
  choice on your terminal program)  and the format
  is 8-N-1.  During certain operations, the PC is
  sending data as fast as the agreed upon protocol
  allows
•  
• a) how fast is data arriving at your embedded
  system in bytes/sec?
•  
•  
•  
• b) how much time after the stop bit arrives at
  the Rabbit do you have to read the data from the
  serial port? (to guarantee that no data is lost
  or corrupted)
•  
•  
•  
•  
•  
• c)  Assuming that you are trying to operate the
  serial port (serial port B) by polling, which
  register do you check? What in that register lets
  you know that a byte has arrived?
•  
•  
•  
•  

32
UDP Overview

• TCP
• Connection oriented a connection must be made
  before date is exchanged (i.e., a point-to-point
  protocol)
• Stream oriented all packets are part of a
  stream, whose delivery and order are guaranteed
• Checksum protects data integrity

• UDP
• Connectionless data is sent/received w/o a
  connection be formed (is targeted to a particular
  address/port) this allows broadcast messages
• Datagrams are are sent without a guarantee of
  their delivery (faster/simpler)
• Checksum protects data integrity

Note that while TCP takes more resources, since
generally one works with a library, the use of
the more complicated protocol may likely make
life easier.
33
TCP/UDP Socket Operation
Note that no connection is necessary, so
broadcast is possible /define REMOTE_IP
"255.255.255.255" /broadcast/
34
UDP Functions

• sock_init() still need to initialize
• tcp_tick() still need to run stack
• int udp_open( udp_Socket s, word lport, longword
  remip, word port, dataHandler_t datahandler )
  Opens a UDP socket on the given port. Various
  settings for IP address (given, 0, -1), and port
  (given, 0)
• int udp_send(udp_Socket s, char buffer, int
  len) sends a UDP packet
• int udp_recv(udp_Socket s, char buffer, int
  len) receives a UDP packet

35

• .
• .
• state 0
• sock_init()
• /printf("Opening UDP socket\n")/
• if(!udp_open(sock, LOCAL_PORT,
  resolve(REMOTE_IP), REMOTE_PORT, NULL))
• printf("udp_open failed!\n")
• exit(0)
• / send heartbeats /
• for()
• //putchar('.')
• tcp_tick(NULL)
• switch (state)
• case 0
• if (TimeElapsed(1))
• state 1

36
C\DCRABBIT_8.10\Samples\RCM3000\TCPIP\echo_server
.c

• while(1)
• switch(state)
• case 0/INITIALIZATION/ // listen for
  incoming connection
• tcp_listen(sock,MY_PORT,INCOMING_IP,INCOMING_P
  ORT,NULL,0)
• MS_TIMER 0L
• state // init complete move onto next
  state
• break
• case 1/LISTEN/
• if(sock_established(sock)) // check for a
  connection
• state // we have connection so move on
• else if (MS_TIMER gt TIME_OUT) // if 1 sec and
  no sock
• state 4 // abort and re-init
• break
• case 2/RECEIVE/
• state receive_packet() // see function for
  details
• if (MS_TIMER gt TIME_OUT) // if 1 sec and still
  waiting
• state 4 // abort and re-init

37
Backup
38
Watchdog Timer

• 17-bit Counter
• Free runs on 32.768kHz oscillator if enabled
• When counter reaches predetermined value, pulse
  from output resets processor
• 250ms,500ms,1s,2s
• Software disables this reset by writing to WDTCR
  before the output reaches the predetermined
  value.
• Resets the timer and sets the future compare
  value
• Dynamic C is handling for us in BIOS

R3000 Users Manual 7.8 has some software
suggestions
39
Drive Control

• Port D,F,G have configurable output drivers as
  set by PxDCR
• 0 Default Driver drives output high and low
  depending
• 1 Open Drain Driver drives low only,
  presumably pulled high by an external resistor

Picture Here
Ref R3000 UM Sec. 4.2