kopia lustrzana https://github.com/F5OEO/rpitx
451 wiersze
13 KiB
C++
451 wiersze
13 KiB
C++
/*MIT License
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Copyright (c) 2016 Galen Alderson
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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Fork and modification for rpitx (c)(F5OEO 2018)
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <string.h>
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#include <strings.h>
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#include <time.h>
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#include <unistd.h>
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#include "../librpitx/src/librpitx.h"
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#define PROGRAM_VERSION "0.1"
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//Check out main() at the bottom of the file
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//You can modify MIN_DELAY and MAX_DELAY to fit your needs.
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//Check out https://en.wikipedia.org/wiki/POCSAG
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//Also see http://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.584-2-199711-I!!PDF-E.pdf
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//They'll be handy when trying to understand this stuff.
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//The sync word exists at the start of every batch.
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//A batch is 16 words, so a sync word occurs every 16 data words.
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#define SYNC 0x7CD215D8
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//The idle word is used as padding before the address word, and at the end
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//of a message to indicate that the message is finished. Interestingly, the
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//idle word does not have a valid CRC code, while the sync word does.
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#define IDLE 0x7A89C197
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//One frame consists of a pair of two words
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#define FRAME_SIZE 2
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//One batch consists of 8 frames, or 16 words
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#define BATCH_SIZE 16
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//The preamble comes before a message, and is a series of alternating
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//1,0,1,0... bits, for at least 576 bits. It exists to allow the receiver
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//to synchronize with the transmitter
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#define PREAMBLE_LENGTH 576
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//These bits appear as the first bit of a word, 0 for an address word and
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//one for a data word
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#define FLAG_ADDRESS 0x000000
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#define FLAG_MESSAGE 0x100000
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//The last two bits of an address word's data represent the data type
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//0x3 for text, and 0x0 for numeric.
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#define FLAG_TEXT_DATA 0x3
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#define FLAG_NUMERIC_DATA = 0x0;
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//Each data word can contain 20 bits of text information. Each character is
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//7 bits wide, ASCII encoded. The bit order of the characters is reversed from
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//the normal bit order; the most significant bit of a word corresponds to the
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//least significant bit of a character it is encoding. The characters are split
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//across the words of a message to ensure maximal usage of all bits.
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#define TEXT_BITS_PER_WORD 20
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//As mentioned above, characters are 7 bit ASCII encoded
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#define TEXT_BITS_PER_CHAR 7
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//Length of CRC codes in bits
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#define CRC_BITS 10
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//The CRC generator polynomial
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#define CRC_GENERATOR 0b11101101001
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/**
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* Calculate the CRC error checking code for the given word.
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* Messages use a 10 bit CRC computed from the 21 data bits.
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* This is calculated through a binary polynomial long division, returning
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* the remainder.
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* See https://en.wikipedia.org/wiki/Cyclic_redundancy_check#Computation
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* for more information.
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*/
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uint32_t crc(uint32_t inputMsg) {
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//Align MSB of denominatorerator with MSB of message
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uint32_t denominator = CRC_GENERATOR << 20;
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//Message is right-padded with zeroes to the message length + crc length
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uint32_t msg = inputMsg << CRC_BITS;
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//We iterate until denominator has been right-shifted back to it's original value.
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for (int column = 0; column <= 20; column++) {
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//Bit for the column we're aligned to
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int msgBit = (msg >> (30 - column)) & 1;
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//If the current bit is zero, we don't modify the message this iteration
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if (msgBit != 0) {
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//While we would normally subtract in long division, we XOR here.
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msg ^= denominator;
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}
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//Shift the denominator over to align with the next column
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denominator >>= 1;
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}
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//At this point 'msg' contains the CRC value we've calculated
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return msg & 0x3FF;
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}
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/**
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* Calculates the even parity bit for a message.
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* If the number of bits in the message is even, return 0, else return 1.
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*/
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uint32_t parity(uint32_t x) {
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//Our parity bit
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uint32_t p = 0;
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//We xor p with each bit of the input value. This works because
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//xoring two one-bits will cancel out and leave a zero bit. Thus
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//xoring any even number of one bits will result in zero, and xoring
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//any odd number of one bits will result in one.
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for (int i = 0; i < 32; i++) {
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p ^= (x & 1);
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x >>= 1;
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}
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return p;
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}
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/**
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* Encodes a 21-bit message by calculating and adding a CRC code and parity bit.
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*/
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uint32_t encodeCodeword(uint32_t msg) {
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uint32_t fullCRC = (msg << CRC_BITS) | crc(msg);
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uint32_t p = parity(fullCRC);
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return (fullCRC << 1) | p;
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}
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/**
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* ASCII encode a null-terminated string as a series of codewords, written
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* to (*out). Returns the number of codewords written. Caller should ensure
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* that enough memory is allocated in (*out) to contain the message
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*
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* initial_offset indicates which word in the current batch the function is
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* beginning at, so that it can insert SYNC words at appropriate locations.
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*/
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uint32_t encodeASCII(uint32_t initial_offset, char* str, uint32_t* out) {
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//Number of words written to *out
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uint32_t numWordsWritten = 0;
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//Data for the current word we're writing
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uint32_t currentWord = 0;
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//Nnumber of bits we've written so far to the current word
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uint32_t currentNumBits = 0;
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//Position of current word in the current batch
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uint32_t wordPosition = initial_offset;
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while (*str != 0) {
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unsigned char c = *str;
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str++;
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//Encode the character bits backwards
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for (int i = 0; i < TEXT_BITS_PER_CHAR; i++) {
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currentWord <<= 1;
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currentWord |= (c >> i) & 1;
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currentNumBits++;
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if (currentNumBits == TEXT_BITS_PER_WORD) {
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//Add the MESSAGE flag to our current word and encode it.
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*out = encodeCodeword(currentWord | FLAG_MESSAGE);
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out++;
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currentWord = 0;
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currentNumBits = 0;
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numWordsWritten++;
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wordPosition++;
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if (wordPosition == BATCH_SIZE) {
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//We've filled a full batch, time to insert a SYNC word
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//and start a new one.
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*out = SYNC;
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out++;
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numWordsWritten++;
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wordPosition = 0;
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}
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}
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}
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}
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//Write remainder of message
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if (currentNumBits > 0) {
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//Pad out the word to 20 bits with zeroes
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currentWord <<= 20 - currentNumBits;
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*out = encodeCodeword(currentWord | FLAG_MESSAGE);
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out++;
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numWordsWritten++;
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wordPosition++;
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if (wordPosition == BATCH_SIZE) {
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//We've filled a full batch, time to insert a SYNC word
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//and start a new one.
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*out = SYNC;
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out++;
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numWordsWritten++;
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wordPosition = 0;
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}
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}
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return numWordsWritten;
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}
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/**
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* An address of 21 bits, but only 18 of those bits are encoded in the address
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* word itself. The remaining 3 bits are derived from which frame in the batch
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* is the address word. This calculates the number of words (not frames!)
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* which must precede the address word so that it is in the right spot. These
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* words will be filled with the idle value.
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*/
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int addressOffset(int address) {
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return (address & 0x3) * FRAME_SIZE;
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}
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/**
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* Encode a full text POCSAG transmission addressed to (address).
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* (*message) is a null terminated C string.
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* (*out) is the destination to which the transmission will be written.
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*/
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void encodeTransmission(int address, char* message, uint32_t* out) {
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//Encode preamble
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//Alternating 1,0,1,0 bits for 576 bits, used for receiver to synchronize
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//with transmitter
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for (int i = 0; i < PREAMBLE_LENGTH / 32; i++) {
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*out = 0xAAAAAAAA;
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out++;
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}
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uint32_t* start = out;
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//Sync
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*out = SYNC;
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out++;
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//Write out padding before adderss word
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int prefixLength = addressOffset(address);
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for (int i = 0; i < prefixLength; i++) {
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*out = IDLE;
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out++;
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}
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//Write address word.
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//The last two bits of word's data contain the message type
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//The 3 least significant bits are dropped, as those are encoded by the
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//word's location.
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*out = encodeCodeword( ((address >> 3) << 2) | FLAG_TEXT_DATA);
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out++;
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//Encode the message itself
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out += encodeASCII(addressOffset(address) + 1, message, out);
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//Finally, write an IDLE word indicating the end of the message
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*out = IDLE;
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out++;
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//Pad out the last batch with IDLE to write multiple of BATCH_SIZE + 1
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//words (+ 1 is there because of the SYNC words)
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size_t written = out - start;
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size_t padding = (BATCH_SIZE + 1) - written % (BATCH_SIZE + 1);
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for (size_t i = 0; i < padding; i++) {
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*out = IDLE;
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out++;
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}
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}
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/**
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* Calculates the length in words of a text POCSAG message, given the address
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* and the number of characters to be transmitted.
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*/
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size_t textMessageLength(int address, int numChars) {
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size_t numWords = 0;
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//Padding before address word.
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numWords += addressOffset(address);
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//Address word itself
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numWords++;
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//numChars * 7 bits per character / 20 bits per word, rounding up
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numWords += (numChars * TEXT_BITS_PER_CHAR + (TEXT_BITS_PER_WORD - 1))
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/ TEXT_BITS_PER_WORD;
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//Idle word representing end of message
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numWords++;
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//Pad out last batch with idles
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numWords += BATCH_SIZE - (numWords % BATCH_SIZE);
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//Batches consist of 16 words each and are preceded by a sync word.
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//So we add one word for every 16 message words
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numWords += numWords / BATCH_SIZE;
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//Preamble of 576 alternating 1,0,1,0 bits before the message
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//Even though this comes first, we add it to the length last so it
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//doesn't affect the other word-based calculations
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numWords += PREAMBLE_LENGTH / 32;
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return numWords;
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}
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void SendFsk(uint64_t Freq,uint32_t *Message,int Size)
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{
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//int SR=40625;
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int SR=1200;
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float Deviation=4500;
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int FiFoSize=12000;
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fprintf(stderr,"Fifo Size =%d, Size = %d",FiFoSize,Size);
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fskburst fsktest(Freq,SR,Deviation,14,FiFoSize);
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unsigned char *TabSymbol=(unsigned char *)malloc(Size*32);
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int Sym=0;
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for(int i=0;i<Size;i++)
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{
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for(int j=31;j>=0;j--)
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{
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TabSymbol[Sym]=(Message[i]>>j)&0x1;
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//fprintf(stderr,"%x ",TabSymbol[Sym]);
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Sym++;
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}
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}
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//fprintf(stderr,"Symbols=%d\n",Sym);
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fsktest.SetSymbols(TabSymbol,Sym);
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sleep(1);
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/*for(i=0;i<FiFoSize;i++)
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{
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TabSymbol[i]=1;
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}
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fsktest.SetSymbols(TabSymbol,FiFoSize);
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sleep(1);*/
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fsktest.stop();
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}
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void print_usage(void)
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{
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fprintf(stderr,\
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"\npocsag -%s\n\
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Usage:\npocsag [-f Frequency] \n\
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-f float central frequency Hz(50 kHz to 1500 MHz),\n\
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-? help (this help).\n\
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\n",\
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PROGRAM_VERSION);
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} /* end function print_usage */
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int main(int argc, char* argv[]) {
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//Read in lines from STDIN.
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//Lines are in the format of address:message
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//The program will encode transmissions for each message, writing them
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//to STDOUT. It will also encode a rand amount of silence between them,
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//from 1-10 seconds in length, to act as a simulated "delay".
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int a;
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int anyargs = 1;
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uint64_t SetFrequency=439875000L;
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while(1)
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{
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a = getopt(argc, argv, "f:");
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if(a == -1)
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{
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if(anyargs) break;
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else a='h'; //print usage and exit
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}
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anyargs = 1;
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switch(a)
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{
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case 'f': // Frequency
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SetFrequency = atof(optarg);
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break;
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default:
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print_usage();
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exit(1);
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break;
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}/* end switch a */
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}/* end while getopt() */
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char line[65536];
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srand(time(NULL));
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for (;;) {
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if (fgets(line, sizeof(line), stdin) == NULL) {
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//Exit on EOF
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return 0;
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}
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size_t colonIndex = 0;
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for (size_t i = 0; i < sizeof(line); i++) {
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if (line[i] == 0) {
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fputs("Malformed Line!", stderr);
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return 1;
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}
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if (line[i] == ':') {
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colonIndex = i;
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break;
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}
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}
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int address = (int) strtol(line, NULL, 10);
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char* message = line + colonIndex + 1;
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size_t messageLength = textMessageLength(address, strlen(message));
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uint32_t* transmission =
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(uint32_t*) malloc(sizeof(uint32_t) * messageLength+2);
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encodeTransmission(address, message, transmission);
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SendFsk(SetFrequency,transmission,messageLength);
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//Generate rand amount of silence. Silence is a sample with
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//a value of 0.
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}
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}
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