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nec.c
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nec.c
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#include <stdint.h>
#include "nec.h"
static uint8_t state;
static uint8_t edge_count;
static uint16_t edges[NEC_MAX_EDGES];
static uint8_t addr;
static uint8_t cmd;
/* nec_init intializes the internals for use */
void nec_init(void)
{
addr = 0;
cmd = 0;
edge_count = 0;
nec_reset();
}
/* nec_reset resets the decoder to the state present after calling nec_init. this is called
* internally, but should also be called after calling nec_get_addr and nec_get_cmd after a
* successful decode */
void nec_reset(void)
{
state = STATE_NONE;
edge_count = 0;
}
/* nec_add_edge adds an edge to the store for future processing. duration should be
* a 16 bit integer representing the clock ticks since the last edge */
void nec_add_edge(uint16_t duration)
{
if(edge_count < NEC_MAX_EDGES) {
edges[edge_count++] = duration;
} else { /* too many edges */
nec_reset();
}
}
/* nec_get_address returns the address from an NEC command. should be called
* after a call to nec_decode if nec_get_state returns a successful read */
uint8_t nec_get_addr(void)
{
return addr;
}
/* nec_get_cmd returns the command from an NEC command. should be called
* after a call to nec_decode if nec_get_state returns a successful read */
uint8_t nec_get_cmd(void)
{
return cmd;
}
/* nec_get_state returns the current state of the NEC decoder */
uint8_t nec_get_state(void)
{
return state;
}
/* nec_decode takes all of the added edges and decodes it, extracting the
* address and command. */
void nec_decode(void)
{
/* if the edge count isnt that of a complete command or a repeat packet
* then we don't no what it is. discard */
if(edge_count != NEC_PACKET_EDGE_COUNT && edge_count != NEC_REPEAT_PACKET_EDGE_COUNT) {
nec_reset();
return;
}
/* store address and command bytes here until we verify correctness.
* then we can copy it to the global buffers accessed by get functions */
uint8_t temp_addr;
uint8_t temp_cmd;
temp_addr = temp_cmd = 0;
uint8_t edge_index;
uint16_t curr_edge;
uint16_t next_edge;
for(edge_index = 0; edge_index < edge_count; edge_index++) {
curr_edge = edges[edge_index];
next_edge = edges[edge_index + 1];
switch(state) {
case STATE_NONE:
if(next_edge >= NEC_START_PULSE_MIN && next_edge <= NEC_START_PULSE_MAX) {
edge_index += 1; /* skip one, and the for loop will increment one more */
state = STATE_RECEIVED_START_PULSE;
} else {
nec_reset();
}
break;
case STATE_RECEIVED_START_PULSE:
/* immediately after the start pulse there is an extended low period. if it's not there
* then this signal is either bad, or a repeat code. repeat code has a low period half
* that of a standard packet. */
if(edge_index + 2 == edge_count) {
nec_reset();
state = STATE_SUCCESSFUL_READ;
return;
}
if(!(curr_edge >= NEC_POST_START_PAUSE_MIN && curr_edge <= NEC_POST_START_PAUSE_MAX)) {
nec_reset();
break;
}
/* we're expecting the first bit of the address here */
if(!(next_edge >= NEC_BIT_PULSE_MIN && next_edge <= NEC_BIT_PULSE_MAX)) {
nec_reset();
break;
}
/* we should be at start edge of the first bit of the 8 bit address. so if
* there are less than 16 edges (8 bits) something is wrong */
if(edge_count < edge_index + 16) {
nec_reset();
break;
}
/* decode the address byte */
temp_addr = __nec_decode_byte(edge_index);
state = STATE_RECEIVED_ADDRESS;
edge_index += 15;
break;
case STATE_RECEIVED_ADDRESS:
/* we're expecting the first bit of the inverse address byte */
if(!(next_edge >= NEC_BIT_PULSE_MIN && next_edge <= NEC_BIT_PULSE_MAX)) {
nec_reset();
break;
}
/* we should be at start edge of the first bit of the 8 bit address inverse.
* so if there are less than 16 edges (8 bits) something is wrong */
if(edge_count < edge_index + 16) {
nec_reset();
break;
}
/* read in the inverse address byte, invert it, and compare it to the address
* byte we already have. if it doesn't match we have an error */
uint8_t inverse_addr;
inverse_addr = __nec_decode_byte(edge_index);
if((inverse_addr ^ temp_addr) == 0) {
nec_reset();
break;
}
state = STATE_RECEIVED_ADDR_INVERSE;
edge_index += 15;
break;
case STATE_RECEIVED_ADDR_INVERSE:
/* we're expecting the first bit of the command byte */
if(!(next_edge >= NEC_BIT_PULSE_MIN && next_edge <= NEC_BIT_PULSE_MAX)) {
nec_reset();
break;
}
/* we should be at start edge of the first bit of the 8 bit command.
* so if there are less than 16 edges (8 bits) something is wrong */
if(edge_count < edge_index + 16) {
nec_reset();
break;
}
/* decode command byte */
temp_cmd = __nec_decode_byte(edge_index);
state = STATE_RECEIVED_COMMAND;
edge_index += 15;
break;
case STATE_RECEIVED_COMMAND:
/* we're expecting the first bit of the command inverse byte */
if(!(next_edge >= NEC_BIT_PULSE_MIN && next_edge <= NEC_BIT_PULSE_MAX)) {
nec_reset();
break;
}
/* we should be at start edge of the first bit of the 8 bit inverse
* command. so if there are less than 16 edges (8 bits) something is wrong */
if(edge_count < edge_index + 16) {
nec_reset();
break;
}
uint8_t inverse_cmd;
inverse_cmd = __nec_decode_byte(edge_index);
if((inverse_cmd ^ temp_cmd) == 0) {
nec_reset();
break;
}
state = STATE_RECEIVED_COMMAND_INVERSE;
edge_index += 15;
break;
case STATE_RECEIVED_COMMAND_INVERSE:
/* we're expecting the stop bit */
if(!(next_edge >= NEC_BIT_PULSE_MIN && next_edge <= NEC_BIT_PULSE_MAX)) {
nec_reset();
break;
}
addr = temp_addr;
cmd = temp_cmd;
state = STATE_SUCCESSFUL_READ;
break;
}
}
}
uint8_t __nec_decode_byte(uint8_t offset)
{
uint8_t addr;
addr = 0;
uint8_t x;
uint16_t phase_end_ts;
for(addr = 0, x = 1; x < 9; x++) {
phase_end_ts = edges[offset + (x * 2) + 2];
if(phase_end_ts > NEC_1_BIT_TRANSMIT_TIME_MIN) {
addr |= (1 << (8 - x));
}
}
return addr;
}