Onewire

Github Repo	C Header	C source	JS source
mongoose-os-libs/arduino-onewire	OneWire.h		api_arduino_onewire.js

This library provides an Arduino compatibility layer for onewire by providing an OneWire.h public header, so that one could pick an existing Arduino program which uses onewire, throw it into the Mongoose OS application sources, and ideally, it "just works".

Additionally, a mgos-specific API is available, see include/mgos_arduino_onewire.h and mjs_fs/api_arduino_onewire.js.

reset

uint8_t reset(void);

Perform a 1-Wire reset cycle. Returns 1 if a device responds with a presence pulse. Returns 0 if there is no device or the bus is shorted or otherwise held low for more than 250uS

select

void select(const uint8_t rom[8]);

Issue a 1-Wire rom select command, you do the reset first.

skip

void skip(void);

Issue a 1-Wire rom skip command, to address all on bus.

write

void write(uint8_t v, uint8_t power = 0);

Write a byte. If 'power' is one then the wire is held high at the end for parasitically powered devices. You are responsible for eventually depowering it by calling depower() or doing another read or write.

read

uint8_t read(void);

Read a byte.

write_bit

void write_bit(uint8_t v);

Write a bit. The bus is always left powered at the end, see note in write() about that.

read_bit

uint8_t read_bit(void);

Read a bit.

depower

void depower(void);

Stop forcing power onto the bus. You only need to do this if you used the 'power' flag to write() or used a write_bit() call and aren't about to do another read or write. You would rather not leave this powered if you don't have to, just in case someone shorts your bus.

reset_search

void reset_search();

Clear the search state so that if will start from the beginning again.

target_search

void target_search(uint8_t family_code);

Setup the search to find the device type 'family_code' on the next call to search(*newAddr) if it is present.

search

uint8_t search(uint8_t *newAddr, bool search_mode = true);

Look for the next device. Returns 1 if a new address has been returned. A zero might mean that the bus is shorted, there are no devices, or you have already retrieved all of them. It might be a good idea to check the CRC to make sure you didn't get garbage. The order is deterministic. You will always get the same devices in the same order.

crc8

static uint8_t crc8(const uint8_t *addr, uint8_t len);
  
 private:
  struct mgos_onewire *ow_;  // The mgos_onewire handle
};

Compute a Dallas Semiconductor 8 bit CRC, these are used in the ROM and scratchpad registers.

JS API

OneWire.create

OneWire.create()

Create a OneWire object instance. Return value: an object with the methods described below.

myOW.close

myOW.close()

Close OneWire handle. Return value: none.

myOW.reset

myOW.reset()

Reset the 1-wire bus. Usually this is needed before communicating with any device.

myOW.select

myOW.select(addr)

Select a device based on its address addr, which is a 8-byte string. After a reset, this is needed to choose which device you will use, and then all communication will be with that device, until another reset. Example:

myOW.select("\x28\xff\x2b\x45\x4c\x04\x00\x10");

myOW.skip

myOW.skip()

Skip the device selection. This only works if you have a single device, but you can avoid searching and use this to immediately access your device.

myOW.write

myOW.write(v)

Write a byte to the onewire bus. Example:

// Write 0x12 to the onewire bus
myOW.write(0x12);

myOW.write_bytes

myOW.write_bytes(buf, len)

Write first len bytes of the string buf. Example:

// Write [0x55, 0x66, 0x77] to the onewire bus
myOW.write_bytes("\x55\x66\x77", 3);

myOW.read

myOW.read()

Read a byte from the onewire bus. Example:

let b = myOW.read();
print('read:', b);

myOW.read_bytes

myOW.read_bytes(buf, len)

Read multiple bytes from the onewire bus. The given buffer should be large enough to fit the data; otherwise it will result in memory corruption and thus undefined behavior. Return value: none. Example:

let buf = "          ";
myOW.read_bytes(buf, 10);
print('read:', buf);

myOW.write_bit

myOW.write_bit(v)

Write a single bit to the onewire bus. Given v should be a number: either 0 or 1.

myOW.read_bit

myOW.read_bit()

Read a single bit from the onewire bus. Returned value is either 0 or 1.

myOW.depower

myOW.depower()

Not implemented yet.

myOW.search

myOW.search(addr, mode)

Search for the next device. The given addr should be an string containing least 8 bytes (any bytes). If a device is found, addr is filled with the device's address and 1 is returned. If no more devices are found, 0 is returned. mode is an integer: 0 means normal search, 1 means conditional search. Example:

let addr = "        ";
let res = myOW.search(addr, 0);
if (res === 1) {
  print("Found:", addr);
} else {
  print("Not found");
}

myOW.reset_search

myOW.reset_search()

Reset a search. Next use of myOW.search(....) will begin at the first device.

myOW.target_search

myOW.target_search(fc)

Setup the search to find the device type 'fc' (family code) on the next call to myOW.search() if it is present.

If no devices of the desired family are currently on the bus, then device of some another type will be found by search().

myOW.crc8

myOW.crc8(buf, len)

Calculate crc8 for the first len bytes of a string buf. Example:

// Calculate crc8 of the buffer
let s = "foobar";
let crc = myOW.crc8(s, 6);
print("crc:", crc);

myOW.delay

myOW.delay(t)

Delay t milliseconds.

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