136 lines
4.6 KiB
C
136 lines
4.6 KiB
C
/*
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The MIT License (MIT)
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Copyright (c) 2016 Fred Sundvik
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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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*/
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#include "serial_link/protocol/byte_stuffer.h"
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#include "serial_link/protocol/frame_validator.h"
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#include "serial_link/protocol/physical.h"
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#include <stdbool.h>
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// This implements the "Consistent overhead byte stuffing protocol"
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// https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
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// http://www.stuartcheshire.org/papers/COBSforToN.pdf
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typedef struct byte_stuffer_state {
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uint16_t next_zero;
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uint16_t data_pos;
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bool long_frame;
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uint8_t data[MAX_FRAME_SIZE];
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} byte_stuffer_state_t;
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static byte_stuffer_state_t states[NUM_LINKS];
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void init_byte_stuffer_state(byte_stuffer_state_t* state) {
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state->next_zero = 0;
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state->data_pos = 0;
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state->long_frame = false;
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}
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void init_byte_stuffer(void) {
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int i;
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for (i = 0; i < NUM_LINKS; i++) {
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init_byte_stuffer_state(&states[i]);
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}
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}
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void byte_stuffer_recv_byte(uint8_t link, uint8_t data) {
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byte_stuffer_state_t* state = &states[link];
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// Start of a new frame
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if (state->next_zero == 0) {
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state->next_zero = data;
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state->long_frame = data == 0xFF;
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state->data_pos = 0;
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return;
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}
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state->next_zero--;
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if (data == 0) {
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if (state->next_zero == 0) {
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// The frame is completed
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if (state->data_pos > 0) {
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validator_recv_frame(link, state->data, state->data_pos);
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}
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} else {
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// The frame is invalid, so reset
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init_byte_stuffer_state(state);
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}
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} else {
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if (state->data_pos == MAX_FRAME_SIZE) {
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// We exceeded our maximum frame size
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// therefore there's nothing else to do than reset to a new frame
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state->next_zero = data;
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state->long_frame = data == 0xFF;
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state->data_pos = 0;
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} else if (state->next_zero == 0) {
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if (state->long_frame) {
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// This is part of a long frame, so continue
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state->next_zero = data;
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state->long_frame = data == 0xFF;
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} else {
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// Special case for zeroes
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state->next_zero = data;
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state->data[state->data_pos++] = 0;
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}
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} else {
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state->data[state->data_pos++] = data;
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}
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}
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}
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static void send_block(uint8_t link, uint8_t* start, uint8_t* end, uint8_t num_non_zero) {
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send_data(link, &num_non_zero, 1);
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if (end > start) {
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send_data(link, start, end - start);
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}
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}
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void byte_stuffer_send_frame(uint8_t link, uint8_t* data, uint16_t size) {
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const uint8_t zero = 0;
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if (size > 0) {
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uint16_t num_non_zero = 1;
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uint8_t* end = data + size;
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uint8_t* start = data;
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while (data < end) {
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if (num_non_zero == 0xFF) {
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// There's more data after big non-zero block
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// So send it, and start a new block
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send_block(link, start, data, num_non_zero);
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start = data;
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num_non_zero = 1;
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} else {
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if (*data == 0) {
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// A zero encountered, so send the block
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send_block(link, start, data, num_non_zero);
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start = data + 1;
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num_non_zero = 1;
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} else {
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num_non_zero++;
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}
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++data;
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}
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}
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send_block(link, start, data, num_non_zero);
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send_data(link, &zero, 1);
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}
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}
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