I would like to know the difference between Serial functions and Stream functions in Ardiuno coding. Both behave in the same way but wat is the difference then?
Stream is the base class that the Serial function inherits.
Copy/paste from the reference:
Stream defines the reading functions in Arduino. When using any core functionality that uses a read() or similar method, you can safely assume it calls on the Stream class. For functions like print(), Stream inherits from the Print class.
References:
https://www.arduino.cc/reference/en/language/functions/communication/stream/
What is the difference between Serial and Stream on the Arduino, and how is Serial.write implemented?
Related
I see this function in Arduino scripts using SPI: ISR (SPI_STC_vect). I am familiar with C but this doesn't seem to follow - it looks like a function though there is no return type definition, and the argument doesn't make sense. I am new to SPI and cannot find much/any documentation online. Other functions which run during an interrupt are called using attachInterrupt, however this doesn't seem to be called anywhere.
ISR() is a macro that introduces an interrupt handler.
SPI_STC_vect is a Serial Transfer Complete interrupt vector.
See here for complete documentation, including the list of available interrupt vectors.
I have been working on HEVC for the past 2 years and recently I was asked to port the code of x265 onto OpenCL for parallel processing. Now, I am still at the starting stage and do see some concerns since Class is not a possibility as x265 uses many classes. Would it be possible to pass the structure since I have some function prototypes within the class. Is it possible to replicate the same onto GPU.
Yes, as you have mentioned that we will not be able to pass a class to the Kernel function. However, you would be able to include the prototypes in the structure and pass it to the GPU. You can refer to this link. passing parameters of an kernel function as C++ struct?
I want to write my own code for managing an Arduino serial port (9bit serial) so I need to bypass the preprogrammed arduino ISR vector for Serial1 TX. I can do that by modifying HardwareSerial1.cpp but I dislike the fact that my code becomes non portable and a potential victim of library updates.
Do you know how to program a different ISR vector without messing into library code? I tried this in my own code to no avail:
//bypass arduino library for serial 1 and use this ISR instead
ISR(UART1_UDRE_vect)
{
9bitSerial.interrupt();
}
The following error is reported, which seems to confirm the approach doesn't work:
ISR.cpp:11:25: error: expected unqualified-id before numeric constant
ISR.cpp:in expansion of macro 'UART1_UDRE_vect'
Any clues?
The safest way, IMHO, is to copy the entire HardwareSerial class to a differently-named class. Then proceed to make your modifications. This is exactly what I did for NeoHWSerial and NeoICSerial: they are copied and renamed from HardwareSerial and AltSoftSerial.
However, all uses of Serialx (instances of HardwareSerial) in a build must be replaced with instances of your class. You won't be able to mix instances of HardwareSerial with your class (duplicate ISR errors). But that's no big deal if your class only adds behavior. Other instances that don't use 9 bits should not be affected. If you don't mind, I'd be interested in folding those changes into NeoHWSerial. I've been occasionally looking at 9-bit serial for NeoSWSerial, too.
I'm studying the tcp/ip implementation, specifically sockets layer, and there's something I don't quite understand about a few structure.
I know that 'struct proto_ops' is used to define the operations, e.g. bind/connect/accept, and every socket has a specified proto_ops.
On the other hand, 'struct proto' defines new protocol and the structure also defines function pointers for accept/bind/setsockopt/getsockopt/etc. methods.
I read lots of code in $linux/net/ and I don't see where does it use the operations defined via 'struct proto', so I'm not sure how these methods are being used in the code?
Could someone clarify this for me?
Thanks.
I think the question is the most headache problem when a newbie try to create a new protocol
Explain:
Both structures have member elements with similar names although they represent different functions
struct prot_ops: used for communication between socket layer and transport layer
struct prot: used for communicate with system calls
Example:
when you call a system call in userspace, ex connect(), prot_ops_connect() will be call first.
In fucntion prot_ops_connect(), we need to call sk->sk_prot->connect()
And sk->sk_prot->connect() will call proto_connect() automatically
Hope this help
You can image like this.There are three layer:
BSD sock->inet sock->tcp/udp sock
corresponding ops:
BSD api->proto_ops->proto
If you read sys_socket() and sys_read(), you will get the same answers.
Hopefully, this can help you:-)
Recently I am studying operating system..I just wanna know:
What’s the difference between a system call (like write()) and a standard library function (like printf())?
A system call is a call to a function that is not part of the application but is inside the kernel. The kernel is a software layer that provides you some basic functionalities to abstract the hardware to you. Roughly, the kernel is something that turns your hardware into software.
You always ultimately use write() to write anything on a peripheral whatever is the kind of device you write on. write() is designed to only write a sequence of bytes, that's all and nothing more. But as write() is considered too basic (you may want to write an integer in ten basis, or a float number in scientific notation, etc), different libraries are provided to you by different kind of programming environments to ease you.
For example, the C programming langage gives you printf() that lets you write data in many different formats. So, you can understand printf() as a function that convert your data into a formatted sequence of bytes and that calls write() to write those bytes onto the output. But C++ gives you cout; Java System.out.println, etc. Each of these functions ends to a call to write() (at least on POSIX systems).
One thing to know (important) is that such a system call is costly! It is not a simple function call because you need to call something that is outside of your own code and the system must ensure that you are not trying to do nasty things, etc. So it is very common in higher print-like function that some buffering is built-in; such that write is not always called, but your data are kept into some hidden structure and written only when it is really needed or necessary (buffer is full or you really want to see the result of your print).
This is exactly what happens when you manage your money. If many people gives you 5 bucks each, you won't go deposit each to the bank! You keep them on your wallet (this is the print) up to the point it is full or you don't want to keep them anymore. Then you go to the bank and make a big deposit (this is the write). And you know that putting 5 bucks to your wallet is much much faster than going to the bank and make the deposit. The bank is the kernel/OS.
System calls are implemented by the operating system, and run in kernel mode. Library functions are implemented in user mode, just like application code. Library functions might invoke system calls (e.g. printf eventually calls write), but that depends on what the library function is for (math functions usually don't need to use the kernel).
System Call's in OS are used in interacting with the OS. E.g. Write() could be used something into the system or into a program.
While Standard Library functions are program specific, E.g. printf() will print something out but it will only be in GUI/command line and wont effect system.
Sorry couldnt comment, because i need 50 reputation to comment.
EDIT: Barmar has good answer
I am writing a small program. At the moment it just reads each line from stdin and prints it to stdout. I can add a call to write in the loop, and it would add a few characters at the end of each line. But when I use printf instead, then all the extra characters are clustered and appear all at once, instead of appearing on each line.
It seems that using printf causes stderr to be buffered. Adding fflush(stdout); after calling printf fixes the discrepancy in output.
I'd like to mention another point that the stdio buffers are maintained in a process’s user-space memory, while system call write transfers data directly to a kernel buffer. It means that if you fork a process after write and printf calls, flushing may bring about to give output three times subject to line-buffering and block-buffering, two of them belong to printf call since stdio buffers are duplicated in the child by fork.
printf() is one of the APIs or interfaces exposed to user space to call functions from C library.
printf() actually uses write() system call. The write() system call is actually responsible for sending data to the output.