Multi Propeller - 8bit Parallel IO

Some simple mechansims for transmission of arrays of data in

eight bit parallel chunks. Sender/receiver synchronization is

accomplished using a request to send (RTS) signal initiated by the

sender. Upon sensing an RTS signal the receiver raises a clear to

send signal (CTS) when it is ready to receive the data. The sender

drops RTS once the data bits are set on the pins and waits for the

receiver to drop CTS thereby indicating it has received the data.

A checksum byte is calculated and transmitted following the last

data byte. The calculated checksum is returned to the caller and

may be examined by calling GetResult. In addition, upon completion

of a receive the internally computed checksum can be examined by

calling GetValue. The receiver can thereby detect a parity error

by comparing GetResult with GetValue. If they disagree, a parity

error has occurred.

The data are buffered in COG memory. Methods are provided to load

the buffer from hub RAM prior to transmission, transmit the buffer,

receive a buffer and to unload the buffer to hub RAM.

The COG buffer is 1KB in size. As a result transmissions may not

exceed that size (1024 bytes or 256 longs). It can however be

increased up to 1380 bytes (345 longs) if needed by changing the

constant MSIZE. At MSIZE=345 all available cog memory is in use.

This object requires one cog for operation.

Clocked at ~390kBytes (3.12Mbits) per second on a pair of 80MHz

Propeller systems sending 1,024 Byte blocks. If you need more

speed you can a) over-clock the processors; b) modify the TxWait

function to reduce the pulse duration of the RTS and data signals

or c) reduce the PIO_waitinc value in Start to shorten the wait

time to less than its current ~476nS value.

Requires 10 I/O pins for operation:

RTS

CTS

MSB...LSB - eight contiguous pins

Example Usage Code:

CON

_clkmode = xtal1 + pll16x ' System clock ‚Üí 80 MHz

_xinfreq = 5_000_000 ' external crystal 5MHz

BUFFERSIZE = PIO#MSIZE

PACKETSIZELONGS= 256

PACKETSIZEBYTES= PACKETSIZELONGS<<2

DATpin = 0 ' 0..7 data bits

RTSpin = 8 ' request to send pin

CTSpin = 9 ' clear to send pin

OBJ

PIO : "ParallelIO"

VAR

long buffer[BUFFERSIZE]

PUB ATransmitter { run this on one propeller }

PIO.Start(PIO#AS_TRANSMITTER,DATpin, RTSpin, CTSpin)

repeat

PIO.LoadBuffer(@buffer,PACKETSIZELONGS)

if not PIO.TransmitBuffer(PACKETSIZEBYTES)

{ deal with transmit timeout }

else

{ do what you will with the buffer content }

PUB AReceiver { runthis on another propeller }

PIO.Start(PIO#AS_RECEIVER, DATpin, RTSpin, CTSpin)

repeat

if PIO.ReceiveBuffer(PACKETSIZEBYTES)

if PIO.GetResult <> PIO.GetValue ' checksum error

{ deal with the parity error }

else

PIO.UnloadBuffer(@buffer,PACKETSIZELONGS)

{ do what you will with the buffer content }

else

{ deal with receive timeout }

PUB AModeSwitcher

{to switch modes}

PIO.Start(<>, DATpin, RTSpin, CTSpin)

..etc..