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uart_ow: Better error handling in corner cases
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Signed-off-by: Brendan Le Foll <[email protected]>
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@arfoll
arfoll committed Apr 15, 2016
1 parent 4a52ad6 commit c41c3b4
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Showing 4 changed files with 71 additions and 43 deletions.
12 changes: 6 additions & 6 deletions api/mraa/uart_ow.h
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Original file line number Diff line number Diff line change
Expand Up @@ -117,18 +117,18 @@ mraa_result_t mraa_uart_ow_stop(mraa_uart_ow_context dev);
* Read a byte from the 1-wire bus
*
* @param dev uart_ow context
* @return the byte read
* @return the byte read or -1 for error
*/
uint8_t mraa_uart_ow_read_byte(mraa_uart_ow_context dev);
int mraa_uart_ow_read_byte(mraa_uart_ow_context dev);

/**
* Write a byte to a 1-wire bus
*
* @param dev uart_ow context
* @param byte the byte to write to the bus
* @return the byte read back during the time slot
* @return the byte read back during the time slot or -1 for error
*/
uint8_t mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte);
int mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte);

/**
* Write a bit to a 1-wire bus and read a bit corresponding to the
Expand All @@ -137,9 +137,9 @@ uint8_t mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte);
*
* @param dev uart_ow context
* @param bit the bit to write to the bus
* @return the bit read back during the time slot
* @return the bit read back during the time slot or -1 for error
*/
uint8_t mraa_uart_ow_bit(mraa_uart_ow_context dev, uint8_t bit);
int mraa_uart_ow_bit(mraa_uart_ow_context dev, uint8_t bit);

/**
* Send a reset pulse to the 1-wire bus and test for device presence
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25 changes: 21 additions & 4 deletions api/mraa/uart_ow.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@ class UartOW
* UartOW Constructor, takes a pin number which will map directly to the
* linux uart number, this 'enables' the uart, nothing more
*
* @throws std::invalid_argument in case of error
* @param uart the index of the uart to use
*/
UartOW(int uart)
Expand All @@ -61,6 +62,7 @@ class UartOW
* UartOW Constructor, takes a string to the path of the serial
* interface that is needed.
*
* @throws std::invalid_argument in case of error
* @param path the file path for the UART to use
*/
UartOW(std::string path)
Expand Down Expand Up @@ -96,24 +98,35 @@ class UartOW
/**
* Read a byte from the 1-wire bus
*
* @throws std::invalid_argument in case of error
* @return the byte read
*/
uint8_t
readByte()
{
return mraa_uart_ow_read_byte(m_uart);
int res = mraa_uart_ow_read_byte(m_uart);
if (res == -1) {
throw std::invalid_argument("Unknown UART_OW error");
}
return (uint8_t) res;
}

/**
* Write a byte to a 1-wire bus
*
* @param byte the byte to write to the bus
*
* @throws std::invalid_argument in case of error
* @return the byte read back during the time slot
*/
uint8_t
writeByte(uint8_t byte)
{
return mraa_uart_ow_write_byte(m_uart, byte);
int res = mraa_uart_ow_write_byte(m_uart, byte);
if (res == -1) {
throw std::invalid_argument("Unknown UART_OW error");
}
return (uint8_t) res;
}

/**
Expand All @@ -122,13 +135,17 @@ class UartOW
* and RX together with a diode, forming a loopback.
*
* @param bit the bit to write to the bus
* @throws std::invalid_argument in case of error
* @return the bit read back during the time slot
*/
bool
writeBit(bool bit)
{
uint8_t rv = mraa_uart_ow_bit(m_uart, (bit) ? 1 : 0);
return ((rv) ? true : false);
int res = mraa_uart_ow_bit(m_uart, (bit) ? 1 : 0);
if (res == -1) {
throw std::invalid_argument("Unknown UART_OW error");
}
return ((res) ? true : false);
}

/**
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3 changes: 1 addition & 2 deletions examples/uart_ow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -58,8 +58,7 @@ main(int argc, char** argv)
uint8_t count = 0;

// start the search from scratch
uint8_t result = mraa_uart_ow_rom_search(uart, 1, id);

mraa_result_t result = mraa_uart_ow_rom_search(uart, 1, id);
if (result == MRAA_ERROR_UART_OW_NO_DEVICES) {
printf("No devices detected.\n");
return 1;
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74 changes: 43 additions & 31 deletions src/uart_ow/uart_ow.c
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Original file line number Diff line number Diff line change
Expand Up @@ -47,43 +47,43 @@ static int LastFamilyDiscrepancy;
static mraa_boolean_t LastDeviceFlag;

// low-level read byte
static unsigned char
read_byte(mraa_uart_ow_context dev)
static mraa_result_t
_ow_read_byte(mraa_uart_ow_context dev, uint8_t *ch)
{
unsigned char ch = 0;

while (!mraa_uart_read(dev, &ch, 1))
while (!mraa_uart_read(dev, (char*) ch, 1))
;

return ch;
return MRAA_SUCCESS;
}

// low-level write byte
static void
write_byte(mraa_uart_ow_context dev, const unsigned char ch)
static int
_ow_write_byte(mraa_uart_ow_context dev, const char ch)
{
mraa_uart_write(dev, &ch, 1);
return mraa_uart_write(dev, &ch, 1);
}

// Here we setup a very simple termios with the minimum required
// settings. We use this to also change speed from high to low. We
// use the low speed (9600 bd) for emitting the reset pulse, and
// high speed (115200 bd) for actual data communications.
//
static void
set_speed(mraa_uart_context dev, mraa_boolean_t speed)
static mraa_result_t
_ow_set_speed(mraa_uart_context dev, mraa_boolean_t speed)
{

if (!dev) {
syslog(LOG_ERR, "uart_ow: set_speed: context is NULL");
return;
return MRAA_ERROR_INVALID_HANDLE;
}

static speed_t baud;
if (speed)
if (speed) {
baud = B115200;
else
}
else {
baud = B9600;
}

struct termios termio = {
.c_cflag = baud | CS8 | CLOCAL | CREAD, .c_iflag = 0, .c_oflag = 0, .c_lflag = NOFLSH, .c_cc = { 0 },
Expand All @@ -94,10 +94,10 @@ set_speed(mraa_uart_context dev, mraa_boolean_t speed)
// TCSANOW is required
if (tcsetattr(dev->fd, TCSANOW, &termio) < 0) {
syslog(LOG_ERR, "uart_ow: tcsetattr() failed");
return;
return MRAA_ERROR_INVALID_RESOURCE;
}

return;
return MRAA_SUCCESS;
}

// Perform the 1-Wire Search Algorithm on the 1-Wire bus using the existing
Expand Down Expand Up @@ -291,31 +291,38 @@ mraa_uart_ow_get_dev_path(mraa_uart_ow_context dev)
return mraa_uart_get_dev_path(dev);
}

uint8_t
int
mraa_uart_ow_bit(mraa_uart_ow_context dev, uint8_t bit)
{
if (!dev) {
syslog(LOG_ERR, "uart_ow: ow_bit: context is NULL");
return 0;
return -1;
}

if (bit)
write_byte(dev, 0xff); /* write a 1 bit */
else
write_byte(dev, 0x00); /* write a 0 bit */
int ret = 0;
uint8_t ch;
if (bit) {
ret = _ow_write_byte(dev, 0xff); /* write a 1 bit */
}
else {
ret = _ow_write_byte(dev, 0x00); /* write a 0 bit */
}

/* return the bit present on the bus (0xff is a '1', anything else
* (typically 0xfc or 0x00) is a 0
*/
return (read_byte(dev) == 0xff);
if (_ow_read_byte(dev, &ch) == -1 || ret == -1) {
return -1;
}
return (ch == 0xff);
}

uint8_t
int
mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte)
{
if (!dev) {
syslog(LOG_ERR, "uart_ow: write_byte: context is NULL");
return 0;
return -1;
}

/* writing bytes - each bit on the byte to send corresponds to a
Expand All @@ -341,12 +348,12 @@ mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte)
return byte;
}

uint8_t
int
mraa_uart_ow_read_byte(mraa_uart_ow_context dev)
{
if (!dev) {
syslog(LOG_ERR, "uart_ow: read_byte: context is NULL");
return 0;
return -1;
}

/* we read by sending 0xff, so the bus is released on the initial
Expand Down Expand Up @@ -379,14 +386,19 @@ mraa_uart_ow_reset(mraa_uart_ow_context dev)
* window. If no device is present, the receive value will equal the
* transmit value. Otherwise the receive value can vary.
*/
set_speed(dev, 0);
if (_ow_set_speed(dev, 0) != MRAA_SUCCESS) {
return MRAA_ERROR_INVALID_HANDLE;
}

/* pull the data line low */
write_byte(dev, 0xf0);
_ow_write_byte(dev, 0xf0);

rv = read_byte(dev);
_ow_read_byte(dev, &rv);

/* back up to high speed for normal data transmissions */
set_speed(dev, 1);
if (_ow_set_speed(dev, 1) != MRAA_SUCCESS) {
return MRAA_ERROR_INVALID_HANDLE;
}

/* shorted data line */
if (rv == 0x00)
Expand Down

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