305 lines
8.0 KiB
C
305 lines
8.0 KiB
C
#include "sss7.h"
|
|
|
|
#include <string.h>
|
|
|
|
|
|
// Current state
|
|
sss7_shared_modfier enum sss7State sss7_state;
|
|
|
|
// Position in the payload for receiving a frame
|
|
uint8_t sss7_rx_pos;
|
|
|
|
// Buffer for the payload for sending a frame
|
|
uint8_t sss7_tx_buffer[SSS7_PAYLOAD_SIZE];
|
|
// Position in the payload for sending a frame
|
|
uint8_t sss7_tx_pos;
|
|
// Crc for the payload used for sending a frame
|
|
uint8_t sss7_tx_crc;
|
|
// The last byte that has been send, used for collison checks in sss7_process_rx
|
|
uint8_t sss7_tx_last_byte;
|
|
// Flag set by sss7_process_rx to indicate that the received byte was sss7_tx_last_byte
|
|
uint8_t sss7_tx_last_ack;
|
|
|
|
// Flag to indicate wheter the last attempt to send a frame failed
|
|
sss7_shared_modfier uint8_t sss7_tx_failed;
|
|
|
|
// Counter that counts milliseconds since the last byte was received
|
|
// Incremented and checked by sss7_process_ticks.
|
|
// Reset by sss7_process_rx.
|
|
uint8_t sss7_timeout_counter;
|
|
|
|
|
|
// Buffers used for receiving payloads with space for SSS7_RX_BUFFER_SIZE payloads
|
|
uint8_t sss7_rx_buffer[SSS7_RX_BUFFER_SIZE][SSS7_PAYLOAD_SIZE];
|
|
// Payload in the buffer to write the received bytes to
|
|
// Note: The payload at sss7_rx_buffer_write can be modified at any time
|
|
// and should therefore never be read by sss7_get_received.
|
|
sss7_shared_modfier uint8_t sss7_rx_buffer_write;
|
|
// Next payload to read by sss7_get_received
|
|
sss7_shared_modfier uint8_t sss7_rx_buffer_read;
|
|
|
|
|
|
/*
|
|
* Initialize sss7 state variables.
|
|
* Resets all buffer positions to 0 and sets state to idle.
|
|
*/
|
|
void sss7_init(void) {
|
|
sss7_state = SSS7_IDLE;
|
|
|
|
sss7_rx_pos = 0;
|
|
sss7_rx_buffer_read = 0;
|
|
sss7_rx_buffer_write = 0;
|
|
|
|
sss7_tx_pos = 0;
|
|
sss7_tx_crc = 0;
|
|
sss7_tx_failed = 0;
|
|
}
|
|
|
|
|
|
/*
|
|
* Internal function to calculate the payload crc.
|
|
* Uses the Maxim iButton 8-bit CRC also known as crc-8-maxim
|
|
* Polynomial: x^8 + x^5 + x^4 + 1 (0x8C)
|
|
* Initial value: 0x0
|
|
*/
|
|
static inline uint8_t sss7_payload_crc(uint8_t buffer[SSS7_PAYLOAD_SIZE]) {
|
|
uint8_t crc = 0;
|
|
|
|
for(uint8_t byte = 0; byte < SSS7_PAYLOAD_SIZE; byte++) {
|
|
crc = crc ^ buffer[byte];
|
|
for (uint8_t bit = 0; bit < 8; bit++)
|
|
{
|
|
if (crc & 0x01) {
|
|
crc = (crc >> 1) ^ 0x8C;
|
|
}
|
|
else {
|
|
crc >>= 1;
|
|
}
|
|
}
|
|
}
|
|
|
|
return crc;
|
|
}
|
|
|
|
|
|
/*
|
|
* Internal function to send a single byte.
|
|
* Assumes that it can use uart_put_byte to actually send the byte.
|
|
*/
|
|
static inline void sss7_send_byte(uint8_t byte) {
|
|
sss7_tx_last_ack = 0;
|
|
sss7_tx_last_byte = byte;
|
|
uart_put_byte(byte);
|
|
}
|
|
|
|
|
|
/*
|
|
* Triggers the transmission of a frame.
|
|
*/
|
|
void sss7_send(uint8_t msg[SSS7_PAYLOAD_SIZE]) {
|
|
// Check that we can send, because we will overwritte the buffer
|
|
if(sss7_state != SSS7_IDLE) {
|
|
sss7_tx_failed = 1;
|
|
return;
|
|
}
|
|
|
|
memcpy(sss7_tx_buffer, msg, SSS7_PAYLOAD_SIZE);
|
|
|
|
sss7_tx_pos = 0;
|
|
sss7_tx_crc = sss7_payload_crc(sss7_tx_buffer);
|
|
|
|
// Commit to send state
|
|
sss7_state = SSS7_TX_HEADER;
|
|
sss7_tx_failed = 0;
|
|
sss7_timeout_counter = 0;
|
|
sss7_send_byte(SSS7_HEADER[0]);
|
|
}
|
|
|
|
/*
|
|
* Handler function for received bytes.
|
|
* Should be called for every received byte, by either interrupts or an eventloop.
|
|
* It also resets the timeout timer.
|
|
* uart_get_byte() is used to retreive the received byte.
|
|
*
|
|
* Note: This handler should by called BEFORE sss7_process_tx when sending.
|
|
*/
|
|
void sss7_process_rx(void) {
|
|
uint8_t byte = uart_get_byte();
|
|
uint8_t crc = 0;
|
|
uint8_t next_buffer_write = 0;
|
|
|
|
// Reset timeout counter
|
|
sss7_timeout_counter = 0;
|
|
|
|
switch((int) sss7_state) {
|
|
// Handle the states for reiceiving a frame first
|
|
case SSS7_IDLE:
|
|
// First received byte should be the first header byte
|
|
if(byte == SSS7_HEADER[0]) {
|
|
sss7_state = SSS7_RX_HEADER;
|
|
}
|
|
else {
|
|
sss7_state = SSS7_IDLE;
|
|
}
|
|
break;
|
|
|
|
case SSS7_RX_HEADER:
|
|
// Second received byte should be the second header byte
|
|
if(byte == SSS7_HEADER[1]) {
|
|
sss7_state = SSS7_RX_PAYLOAD;
|
|
sss7_rx_pos = 0;
|
|
}
|
|
else {
|
|
sss7_state = SSS7_IDLE;
|
|
}
|
|
break;
|
|
|
|
case SSS7_RX_PAYLOAD:
|
|
// Receive the payload
|
|
sss7_rx_buffer[sss7_rx_buffer_write][sss7_rx_pos] = byte;
|
|
sss7_rx_pos++;
|
|
// Check if the payload has been fully received
|
|
if(sss7_rx_pos >= SSS7_PAYLOAD_SIZE) {
|
|
sss7_state = SSS7_RX_CRC;
|
|
}
|
|
break;
|
|
|
|
case SSS7_RX_CRC:
|
|
// Last byte of the frame
|
|
crc = sss7_payload_crc(sss7_rx_buffer[sss7_rx_buffer_write]);
|
|
|
|
// Calculate the next rx buffer position to use
|
|
next_buffer_write = (sss7_rx_buffer_write + 1) % SSS7_RX_BUFFER_SIZE;
|
|
// If the crc is not okay or there are no free buffer positions left,
|
|
// the next frame will be written to the same rx buffer postion.
|
|
// This effectively drops the currrent frame.
|
|
if(byte == crc && next_buffer_write != sss7_rx_buffer_read) {
|
|
sss7_rx_buffer_write = next_buffer_write;
|
|
}
|
|
|
|
// Go back to idle state
|
|
sss7_state = SSS7_IDLE;
|
|
break;
|
|
|
|
// Handle all the TX states
|
|
default:
|
|
// Collision check:
|
|
// If the byte received is not the last byte sent, something went wrong
|
|
if(byte != sss7_tx_last_byte) {
|
|
// Set the failure flag
|
|
sss7_tx_failed = 1;
|
|
// Reset to state to idle
|
|
sss7_state = SSS7_IDLE;
|
|
}
|
|
else {
|
|
// Set the ack flag which is checked by sss7_process_tx
|
|
sss7_tx_last_ack = 1;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* Handler function for sent bytes.
|
|
* Should be called for every compltely sent byte, by either interrupts or an eventloop.
|
|
* Uses uart_put_byte() to send the next byte.
|
|
*
|
|
* Note: This handler should by called AFTER sss7_process_rx when sending.
|
|
*/
|
|
void sss7_process_tx(void) {
|
|
// This handler is called since a byte has been sent and it should have been,
|
|
// read back from the bus and handled by sss7_process_rx by now.
|
|
// So if the last byte sent was acked by everthing is alright
|
|
if(sss7_tx_last_ack) {
|
|
uint8_t byte;
|
|
switch((int) sss7_state) {
|
|
case SSS7_TX_HEADER:
|
|
// First byte of the frame is already sent by sss7_send_byte,
|
|
// this handler is called since its transmission completed.
|
|
// Therefore the second header byte is sent.
|
|
sss7_send_byte(SSS7_HEADER[1]);
|
|
// Reset the position inside the payload
|
|
sss7_tx_pos = 0;
|
|
sss7_state = SSS7_TX_PAYLOAD;
|
|
break;
|
|
|
|
case SSS7_TX_PAYLOAD:
|
|
// Send the next payload byte and increment position
|
|
byte = sss7_tx_buffer[sss7_tx_pos];
|
|
sss7_send_byte(byte);
|
|
sss7_tx_pos++;
|
|
|
|
// All the payload bytes are sent, continue with crc
|
|
if(sss7_tx_pos >= SSS7_PAYLOAD_SIZE) {
|
|
sss7_state = SSS7_TX_CRC;
|
|
}
|
|
break;
|
|
|
|
case SSS7_TX_CRC:
|
|
// Send the crc precalculated by sss_send
|
|
sss7_send_byte(sss7_tx_crc);
|
|
// Reset the state to idle
|
|
sss7_state = SSS7_TX_FINALIZE;
|
|
break;
|
|
|
|
case SSS7_TX_FINALIZE:
|
|
//Not much to do here
|
|
sss7_state = SSS7_IDLE;
|
|
break;
|
|
|
|
default:
|
|
// Controlflow should never ever end up here.
|
|
// Calling the tx handler while being in rx state is messed up.
|
|
break;
|
|
}
|
|
}
|
|
// If the byte was not acked, something went wrong
|
|
else {
|
|
// Set failure flag
|
|
sss7_tx_failed = 1;
|
|
// Reset state to idle
|
|
sss7_state = SSS7_IDLE;
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* Handler function for timeout timer updates.
|
|
* Should be called every once in a while either by interrupts by an eventloop.
|
|
* The ticks parameter is the number of milliseconds that have passed since the last invocation.
|
|
*
|
|
* The timeout basically resolves the scenario where an partial frame is received without errors,
|
|
* but never finished.
|
|
*/
|
|
void sss7_process_ticks(uint16_t ticks) {
|
|
// There are no timeouts in idle state.
|
|
if(sss7_state != SSS7_IDLE) {
|
|
sss7_timeout_counter = sss7_timeout_counter + ticks;
|
|
|
|
if(sss7_timeout_counter > sss7_timeout) {
|
|
switch((int) sss7_state) {
|
|
case SSS7_TX_HEADER:
|
|
case SSS7_TX_PAYLOAD:
|
|
case SSS7_TX_CRC:
|
|
sss7_tx_failed = 1;
|
|
default:
|
|
sss7_state = SSS7_IDLE;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Function to retreive a received frame from the rx buffer.
|
|
*/
|
|
void sss7_get_received(uint8_t msg[SSS7_PAYLOAD_SIZE]) {
|
|
// Make sure that sss7_rx_buffer_write != sss7_rx_buffer_read still holds
|
|
if(sss7_has_received()) {
|
|
// Copy the payload
|
|
memcpy(msg, sss7_rx_buffer[sss7_rx_buffer_read], SSS7_PAYLOAD_SIZE);
|
|
// Move to the next payload in the buffer
|
|
sss7_rx_buffer_read = (sss7_rx_buffer_read + 1) % SSS7_RX_BUFFER_SIZE;
|
|
};
|
|
}
|