Using Chopsticks
Using Commas
Using Chopsticks
Using Cscope
Using Cmpivot

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Hone your C programming skills with the UVa Online Judge. If you are using Windows, you can use the MinGW Windows tutorial to help prepare programs. This website has thousands of datasheets, and is maintained by an engineer that has spent 3 years collecting datasheets as a service to the engineering community.

Ford i promise. 10-5, using C = 0.01 F. For the snubber circuit of Fig. 10-12a, V s = 50, I L = 4 A, C = 0.05 F, R = 5., and t f = 0.5 s. The switching frequency is 120 kHz, and the duty ratio is 0.4. (a) Determine expressions for i Q, i c, and v c during transistor turnoff. (b) Graph the i Q and v C waveforms at turnoff. For the most part, only the first entry - the bdaddr field, which gives the address of the detected device - is of any use. Occasionally, there may be a use for the devclass field, which gives information about the type of device detected (i.e. If it's a printer, phone, desktop computer, etc.) and is described in the Bluetooth Assigned Numbers.

There are reasons to prefer developing Bluetooth applicationsin C instead of in a high level language such as Python. The Pythonenvironment might not be available or might not fit on the target device;strict application requirements on program size, speed, and memory usage maypreclude the use of an interpreted language like Python; the programmer maydesire finer control over the local Bluetooth adapter than PyBluez provides;or the project may be to create a shared library for other applications tolink against instead of a standalone application.As of this writing, BlueZ is a powerful Bluetooth communications stack withextensive APIs that allows a user to fully exploit all local Bluetoothresources, but it has no official documentation. Furthermore, there is verylittle unofficial documentation as well. Novice developers requestingdocumentation on the official mailing lists [1] are typicallyrebuffed and told to figure out the API by reading through the BlueZ sourcecode. This is a time consuming process that can only reveal small pieces ofinformation at a time, and is quite often enough of an obstacle to deter manypotential developers.

This chapter presents a short introduction to developing Bluetoothapplications in C with BlueZ. The tasks covered in chapter 2 are nowexplained in greater detail here for C programmers.

A simple program that detects nearby Bluetooth devices is shown in Example 4-1. The program reserves system Bluetoothresources, scans for nearby Bluetooth devices, and then looks up the userfriendly name for each detected device. A more detailed explanation of thedata structures and functions used follows.

Example 4-1. simplescan.c

4.1.1. Compilation

To compile our program, invoke gcc and link againstlibbluetooth

# gcc -o simplescan simplescan.c -lbluetooth

4.1.2. Explanation

The basic data structure used to specify a Bluetooth device address is thebdaddr_t. All Bluetooth addresses in BlueZ will be storedand manipulated as bdaddr_t structures. BlueZ provides twoconvenience functions to convert between strings andbdaddr_t structures.

str2ba takes an string of the form ``XX:XX:XX:XX:XX:XX',where each XX is a hexadecimal number specifying an octet of the 48-bitaddress, and packs it into a 6-byte bdaddr_t.ba2str does exactly the opposite.

Local Bluetooth adapters are assigned identifying numbers starting with 0, anda program must specify which adapter to use when allocating system resources.Usually, there is only one adapter or it doesn't matter which one is used, sopassing NULL to hci_get_route willretrieve the resource number of the first available Bluetooth adapter.

It is not a good idea to hard-code the devicenumber 0, because that is not always the id of the first adapter. For example,if there were two adapters on the system and the first adapter (id 0) isdisabled, then the first available adapter is the one withid 1.

If there are multiple Bluetooth adapters present, then to choose the adapterwith address ``01:23:45:67:89:AB', pass the char * representation of the address to hci_devid and use that inplace of hci_get_route.

Most Bluetooth operations require the use of an open socket.hci_open_dev is a convenience function that opens aBluetooth socket with the specified resource number [2]. To be clear, the socket openedby hci_open_dev represents a connection to themicrocontroller on the specified local Bluetooth adapter, and not a connectionto a remote Bluetooth device. Performing low level Bluetooth operationsinvolves sending commands directly to the microcontroller with this socket, andSection 4.5 discusses this in greater detail.

After choosing the local Bluetooth adapter to use and allocating systemresources, the program is ready to scan for nearby Bluetooth devices. In theexample, hci_inquiry performs a Bluetooth device discoveryand returns a list of detected devices and some basic information about them inthe variable ii. On error, it returns -1 and setserrno accordingly.

hci_inquiry is one of the few functions that requires theuse of a resource number instead of an open socket, so we use thedev_id returned by hci_get_route. Theinquiry lasts for at most 1.28 * len seconds, and at mostmax_rsp devices will be returned in the output parameterii, which must be large enough to accommodatemax_rsp results. We suggest using amax_rsp of 255 for a standard 10.24 second inquiry.

If flags is set to IREQ_CACHE_FLUSH, thenthe cache of previously detected devices is flushed before performing thecurrent inquiry. Otherwise, if flags is set to 0, then theresults of previous inquiries may be returned, even if the devices aren't inrange anymore.

The inquiry_info structure is defined as

Using Chopsticks

For the most part, only the first entry - the bdaddr field,which gives the address of the detected device - is of any use. Occasionally,there may be a use for the dev_class field, which givesinformation about the type of device detected (i.e. if it's a printer, phone,desktop computer, etc.) and is described in the Bluetooth AssignedNumbers [3]. The rest of the fields are used for lowlevel communication, and are not useful for most purposes. The interestedreader can see the Bluetooth Core Specification [4] for more details.

Once a list of nearby Bluetooth devices and their addresses has been found,the program determines the user-friendly names associated with thoseaddresses and presents them to the user. Thehci_read_remote_name function is used for this purpose.

hci_read_remote_name tries for at mosttimeout milliseconds to use the socketsock to query the user-friendly name of the device withBluetooth address ba. On success,hci_read_remote_name returns 0 and copies at most the firstlen bytes of the device's user-friendly name intoname