//-----------------------------------------------------------------------------
// Send a 1-Wire write bit. Provide 10us recovery time.
//
void OWWriteBit(int bit)
{
bbb_mmio_set_output(pin_);
if (bit)
{
// Write '1' bit
bbb_mmio_set_low(pin_); // Drives DQ low
tickDelay(A);
bbb_mmio_set_high(pin_); // Releases the bus
tickDelay(B); // Complete the time slot and 10us recovery
}
else
{
// Write '0' bit
bbb_mmio_set_low(pin_); // Drives DQ low
tickDelay(C);
bbb_mmio_set_high(pin_); // Releases the bus
tickDelay(D);
}
}
//-----------------------------------------------------------------------------
// Read a bit from the 1-Wire bus and return it. Provide 10us recovery time.
//
int OWReadBit(void)
{
int result;
bbb_mmio_set_output(pin_);
bbb_mmio_set_low(pin_); // Drives DQ low
tickDelay(A);
bbb_mmio_set_high(pin_); // Releases the bus
tickDelay(E);
bbb_mmio_set_input(pin_);
result = bbb_mmio_input(pin_) & 0x01; // Sample the bit value from the slave
tickDelay(F); // Complete the time slot and 10us recovery
return result;
}
//-----------------------------------------------------------------------------
// Generate a 1-Wire reset, return 1 if no presence detect was found,
// return 0 otherwise.
// (NOTE: Does not handle alarm presence from DS2404/DS1994)
//
int OWTouchReset(void)
{
int result;
bbb_mmio_set_output(pin_);
tickDelay(G);
bbb_mmio_set_low(pin_); // Drives DQ low
tickDelay(H);
bbb_mmio_set_high(pin_); // Releases the bus
tickDelay(I);
bbb_mmio_set_input(pin_);
result = bbb_mmio_input(pin_) ^ 0x01; // Sample for presence pulse from slave
tickDelay(J); // Complete the reset sequence recovery
return result; // Return sample presence pulse result
}
int bbb_dht_read(int type, int gpio_base, int gpio_number, float* humidity, float* temperature)
{
int i = 0;
// Validate humidity and temperature arguments and set them to zero.
if (humidity == NULL || temperature == NULL) {
return DHT_ERROR_ARGUMENT;
}
*temperature = 0.0f;
*humidity = 0.0f;
// Store the count that each DHT bit pulse is low and high.
// Make sure array is initialized to start at zero.
int pulseCounts[DHT_PULSES*2] = {0};
// Get GPIO pin and set it as an output.
gpio_t pin;
if (bbb_mmio_get_gpio(gpio_base, gpio_number, &pin) < 0) {
return DHT_ERROR_GPIO;
}
bbb_mmio_set_output(pin);
// Bump up process priority and change scheduler to try to try to make process more 'real time'.
set_max_priority();
// Set pin high for ~500 milliseconds.
bbb_mmio_set_high(pin);
sleep_milliseconds(500);
// The next calls are timing critical and care should be taken
// to ensure no unnecssary work is done below.
// Set pin low for ~20 milliseconds.
bbb_mmio_set_low(pin);
busy_wait_milliseconds(20);
// Set pin as input.
bbb_mmio_set_input(pin);
// Wait for DHT to pull pin low.
uint32_t count = 0;
while (bbb_mmio_input(pin)) {
if (++count >= DHT_MAXCOUNT) {
// Timeout waiting for response.
set_default_priority();
return DHT_ERROR_TIMEOUT;
}
}
// Record pulse widths for the expected result bits.
for (i=0; i < DHT_PULSES*2; i+=2) {
// Count how long pin is low and store in pulseCounts[i]
while (!bbb_mmio_input(pin)) {
if (++pulseCounts[i] >= DHT_MAXCOUNT) {
// Timeout waiting for response.
set_default_priority();
return DHT_ERROR_TIMEOUT;
}
}
// Count how long pin is high and store in pulseCounts[i+1]
while (bbb_mmio_input(pin)) {
if (++pulseCounts[i+1] >= DHT_MAXCOUNT) {
// Timeout waiting for response.
set_default_priority();
return DHT_ERROR_TIMEOUT;
}
}
}
// Done with timing critical code, now interpret the results.
// Drop back to normal priority.
set_default_priority();
// Compute the average low pulse width to use as a 50 microsecond reference threshold.
// Ignore the first two readings because they are a constant 80 microsecond pulse.
uint32_t threshold = 0;
for (i=2; i < DHT_PULSES*2; i+=2) {
threshold += pulseCounts[i];
}
threshold /= DHT_PULSES-1;
// Interpret each high pulse as a 0 or 1 by comparing it to the 50us reference.
// If the count is less than 50us it must be a ~28us 0 pulse, and if it's higher
// then it must be a ~70us 1 pulse.
uint8_t data[5] = {0};
for (i=3; i < DHT_PULSES*2; i+=2) {
int index = (i-3)/16;
data[index] <<= 1;
if (pulseCounts[i] >= threshold) {
// One bit for long pulse.
data[index] |= 1;
}
// Else zero bit for short pulse.
}
// Useful debug info:
//printf("Data: 0x%x 0x%x 0x%x 0x%x 0x%x\n", data[0], data[1], data[2], data[3], data[4]);
// Verify checksum of received data.
if (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
if (type == DHT11) {
// Get humidity and temp for DHT11 sensor.
*humidity = (float)data[0];
*temperature = (float)data[2];
}
else if (type == DHT22) {
// Calculate humidity and temp for DHT22 sensor.
*humidity = (data[0] * 256 + data[1]) / 10.0f;
*temperature = ((data[2] & 0x7F) * 256 + data[3]) / 10.0f;
if (data[2] & 0x80) {
*temperature *= -1.0f;
}
}
return DHT_SUCCESS;
}
else {
return DHT_ERROR_CHECKSUM;
}
}
