Started general cleanup and added comments
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@ -91,7 +91,7 @@ Initial value: 0x0
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### Planned API
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- **Not final, use with caution**
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- All calls are non-blocking,
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any real work should be done by ISRs or an eventloop, which is called peridically.
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any real work should be done by ISRs or an eventloop, which is called periodically.
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- **sss7_can_send()**
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@ -131,8 +131,8 @@ The files are made avaible under the Creative Commons license rev2.5 Attribution
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The Chaos InKL logo is licensed CC BY-NC-SA 3.0.
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The seidenstrasse logo and my personal logo are not avaiable under an open licence.
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The seidenstrasse logo and my personal logo are not available under an open license.
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Therefore you should ask for permission before using the seidenstrasse logo in derived works.
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Also please remove my personal logo if I am not involved in your project.
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The schematics and pcb layout files in hardware are released under the *CERN Open Hardware Licence v1.2*.
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The schematics and pcb layout files in hardware are released under the *CERN Open Hardware License v1.2*.
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@ -2,23 +2,47 @@
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#include <string.h>
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// Current state
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sss7_shared_modfier enum sss7State sss7_state;
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uint8_t sss7_rx_buffer[SSS7_RX_BUFFER_SIZE][SSS7_PAYLOAD_SIZE];
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uint8_t sss7_rx_buffer_write;
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uint8_t sss7_rx_buffer_read;
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// Position in the payload for receiving a frame
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uint8_t sss7_rx_pos;
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// Buffer for the payload for sending a frame
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uint8_t sss7_tx_buffer[SSS7_PAYLOAD_SIZE];
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// Position in the payload for sending a frame
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uint8_t sss7_tx_pos;
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// Crc for the payload used for sending a frame
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uint8_t sss7_tx_crc;
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sss7_shared_modfier uint8_t sss7_tx_failed;
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// The last byte that has been send, used for collison checks in sss7_process_rx
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uint8_t sss7_tx_last_byte;
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// Flag set by sss7_process_rx to indicate that the received byte was sss7_tx_last_byte
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uint8_t sss7_tx_last_ack;
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sss7_shared_modfier uint8_t sss7_timeout_counter;
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// Flag to indicate wheter the last attempt to send a frame failed
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sss7_shared_modfier uint8_t sss7_tx_failed;
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// Counter that counts milliseconds since the last byte was received
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// Incremented and checked by sss7_process_ticks.
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// Reset by sss7_process_rx.
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uint8_t sss7_timeout_counter;
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// Buffers used for receiving payloads with space for SSS7_RX_BUFFER_SIZE payloads
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uint8_t sss7_rx_buffer[SSS7_RX_BUFFER_SIZE][SSS7_PAYLOAD_SIZE];
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// Payload in the buffer to write the received bytes to
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// Note: The payload at sss7_rx_buffer_write can be modified at any time
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// and should therefore never be read by sss7_get_received.
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sss7_shared_modfier uint8_t sss7_rx_buffer_write;
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// Next payload to read by sss7_get_received
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sss7_shared_modfier uint8_t sss7_rx_buffer_read;
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/*
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* Initialize sss7 state variables.
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* Resets all buffer positions to 0 and sets state to idle.
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*/
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void sss7_init(void) {
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sss7_state = SSS7_IDLE;
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@ -32,6 +56,12 @@ void sss7_init(void) {
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}
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/*
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* Internal function to calculate the payload crc.
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* Uses the Maxim iButton 8-bit CRC also known as crc-8-maxim
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* Polynomial: x^8 + x^5 + x^4 + 1 (0x8C)
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* Initial value: 0x0
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*/
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static inline uint8_t sss7_payload_crc(uint8_t buffer[SSS7_PAYLOAD_SIZE]) {
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uint8_t crc = 0;
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@ -52,6 +82,10 @@ static inline uint8_t sss7_payload_crc(uint8_t buffer[SSS7_PAYLOAD_SIZE]) {
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}
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/*
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* Internal function to send a single byte.
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* Assumes that it can use uart_put_byte to actually send the byte.
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*/
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static inline void sss7_send_byte(uint8_t byte) {
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sss7_tx_last_ack = 0;
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sss7_tx_last_byte = byte;
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@ -59,6 +93,9 @@ static inline void sss7_send_byte(uint8_t byte) {
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}
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/*
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* Triggers the transmission of a frame.
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*/
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void sss7_send(uint8_t msg[SSS7_PAYLOAD_SIZE]) {
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// Check that we can send, because we will overwritte the buffer
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if(sss7_state != SSS7_IDLE) {
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@ -78,15 +115,26 @@ void sss7_send(uint8_t msg[SSS7_PAYLOAD_SIZE]) {
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sss7_send_byte(SSS7_HEADER[0]);
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}
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/*
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* Handler function for received bytes.
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* Should be called for every received byte, by either interrupts or an eventloop.
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* It also resets the timeout timer.
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* uart_get_byte() is used to retreive the received byte.
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*
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* Note: This handler should by called BEFORE sss7_process_tx when sending.
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*/
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void sss7_process_rx(void) {
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uint8_t byte = uart_get_byte();
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uint8_t crc = 0;
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uint8_t next_buffer_write = 0;
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// Reset timeout counter
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sss7_timeout_counter = 0;
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switch((int) sss7_state) {
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// Handle the states for reiceiving a frame first
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case SSS7_IDLE:
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// First received byte should be the first header byte
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if(byte == SSS7_HEADER[0]) {
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sss7_state = SSS7_RX_HEADER;
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}
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@ -96,6 +144,7 @@ void sss7_process_rx(void) {
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break;
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case SSS7_RX_HEADER:
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// Second received byte should be the second header byte
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if(byte == SSS7_HEADER[1]) {
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sss7_state = SSS7_RX_PAYLOAD;
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sss7_rx_pos = 0;
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@ -106,31 +155,44 @@ void sss7_process_rx(void) {
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break;
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case SSS7_RX_PAYLOAD:
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// Receive the payload
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sss7_rx_buffer[sss7_rx_buffer_write][sss7_rx_pos] = byte;
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sss7_rx_pos++;
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// Check if the payload has been fully received
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if(sss7_rx_pos >= SSS7_PAYLOAD_SIZE) {
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sss7_state = SSS7_RX_CRC;
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}
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break;
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case SSS7_RX_CRC:
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// Last byte of the frame
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crc = sss7_payload_crc(sss7_rx_buffer[sss7_rx_buffer_write]);
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// Calculate the next rx buffer position to use
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next_buffer_write = (sss7_rx_buffer_write + 1) % SSS7_RX_BUFFER_SIZE;
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// Ensure CRC is okay and we don't overwrite other frames
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// If the crc is not okay or there are no free buffer positions left,
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// the next frame will be written to the same rx buffer postion.
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// This effectively drops the currrent frame.
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if(byte == crc && next_buffer_write != sss7_rx_buffer_read) {
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sss7_rx_buffer_write = next_buffer_write;
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}
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// Go back to idle state
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sss7_state = SSS7_IDLE;
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break;
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// all the TX states
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// Handle all the TX states
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default:
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// Collision check:
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// If the byte received is not the last byte sent, something went wrong
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if(byte != sss7_tx_last_byte) {
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sss7_state = SSS7_IDLE;
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// Set the failure flag
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sss7_tx_failed = 1;
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// Reset to state to idle
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sss7_state = SSS7_IDLE;
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}
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else {
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// Set the ack flag which is checked by sss7_process_tx
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sss7_tx_last_ack = 1;
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}
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break;
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@ -138,42 +200,75 @@ void sss7_process_rx(void) {
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}
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/*
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* Handler function for sent bytes.
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* Should be called for every compltely sent byte, by either interrupts or an eventloop.
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* Uses uart_put_byte() to send the next byte.
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*
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* Note: This handler should by called AFTER sss7_process_rx when sending.
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*/
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void sss7_process_tx(void) {
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// This handler is called since a byte has been sent and it should have been,
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// read back from the bus and handled by sss7_process_rx by now.
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// So if the last byte sent was acked by everthing is alright
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if(sss7_tx_last_ack) {
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uint8_t byte;
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switch((int) sss7_state) {
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case SSS7_TX_HEADER:
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// First byte of the frame is already sent by sss7_send_byte,
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// this handler is called since its transmission completed.
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// Therefore the second header byte is sent.
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sss7_send_byte(SSS7_HEADER[1]);
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sss7_state = SSS7_TX_PAYLOAD;
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// Reset the position inside the payload
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sss7_tx_pos = 0;
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sss7_state = SSS7_TX_PAYLOAD;
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break;
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case SSS7_TX_PAYLOAD:
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// Send the next payload byte and increment position
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byte = sss7_tx_buffer[sss7_tx_pos];
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sss7_send_byte(byte);
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sss7_tx_pos++;
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// All the payload bytes are sent, continue with crc
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if(sss7_tx_pos >= SSS7_PAYLOAD_SIZE) {
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sss7_state = SSS7_TX_CRC;
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}
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break;
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case SSS7_TX_CRC:
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// Send the crc precalculated by sss_send
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sss7_send_byte(sss7_tx_crc);
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// Reset the state to idle
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sss7_state = SSS7_IDLE;
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break;
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default:
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// Controlflow should never ever end up here.
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// Calling the tx handler while being in rx state is messed up.
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break;
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}
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}
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// If the byte was not acked, something went wrong
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else {
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// Set failure flag
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sss7_tx_failed = 1;
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// Reset state to idle
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sss7_state = SSS7_IDLE;
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}
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}
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/*
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* Handler function for timeout timer updates.
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* Should be called every once in a while either by interrupts by an eventloop.
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* The ticks parameter is the number of milliseconds that have passed since the last invocation.
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*
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* The timeout basically resolves the scenario where an partial frame is received without errors,
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* but never finished.
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*/
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void sss7_process_ticks(uint16_t ticks) {
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// There are no timeouts in idle state.
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if(sss7_state != SSS7_IDLE) {
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sss7_timeout_counter = sss7_timeout_counter + ticks;
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}
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}
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/*
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* Function to retreive a received frame from the rx buffer.
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*/
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void sss7_get_received(uint8_t msg[SSS7_PAYLOAD_SIZE]) {
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// Make sure that sss7_rx_buffer_write != sss7_rx_buffer_read still holds
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if(sss7_has_received()) {
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// Copy the payload
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memcpy(msg, sss7_rx_buffer[sss7_rx_buffer_read], SSS7_PAYLOAD_SIZE);
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// Move to the next payload in the buffer
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sss7_rx_buffer_read = (sss7_rx_buffer_read + 1) % SSS7_RX_BUFFER_SIZE;
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};
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}
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@ -36,8 +36,8 @@ const static uint16_t sss7_timeout_increment = 1;
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extern sss7_shared_modfier enum sss7State sss7_state;
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extern sss7_shared_modfier uint8_t sss7_tx_failed;
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extern uint8_t sss7_rx_buffer_write;
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extern uint8_t sss7_rx_buffer_read;
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extern sss7_shared_modfier uint8_t sss7_rx_buffer_write;
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extern sss7_shared_modfier uint8_t sss7_rx_buffer_read;
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void sss7_process_rx(void);
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