|
It's up to you to decide what the upper left corner of a rotated rectangular image is
and how you want it drawn.
You'll have to do a little math, but you have the functions to rotate and position.
Mark
Mark Salsbery
Microsoft MVP - Visual C++
|
|
|
|
|
I am writing an application to communicate with a controller, the data packet size is 7 bytes maximum 14 bytes both ways. I am trying to calculate my worst case frequency and I am using the following approximation, I seem to reall that baud rate is the approximate bit rate.
Max Controller Baud Rate = 500K
Max packet size = 56 bits.
500000/96 = 5.2 KHz
So based on this, and discounting controller and protocol converter latencies, I need to read the serial port every 2 microseconds.
Am I dreaming, or can a small thread handle it? How can I determine what size buffer I need to avoid overflow or loss of data?
Thanks once again for your replies.
|
|
|
|
|
If you are truly talking about serial port usage, the data may be sent by your controller at 500K, but remember that for serial communications, every byte contains eight bits of data, plus (normally) one start bit and one stop bit.
Most serial ports cannot handle more than 115,200 baud (although perhaps some USB-Serial adapters can do better). Additionally, most serial ports provide a buffer that can hold more than one character - typically up to 16 - before you need to read the data.
Given that, at 500000 bps, with 10 bits/character gives 50000 Bytes per second. If you allow the port to buffer the data (let's say 16 characters), then you have 3125 full buffers per second which means a read every 320 microseconds.
The other question is how often does your controller actually send that data. It would appear you may need to send a 7-byte packet to the controller and then you get a 7-byte response from it. If that's the case, you obviously cannot get a response as often as you are calculating - in fact it would be about every 640 microseconds.
If you only query your controller periodically, then you won't get a response until you query, so you're in control of how often you must read the serial port.
Hope that helps.
Karl - WK5M
PP-ASEL-IA (N43CS)
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193
|
|
|
|
|
|
jonsey29847 wrote: ...I need to read the serial port every 2 microseconds.
Are you using a RTOS?
"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
|
|
|
|
|
Yes, however the controller(s) may not send responses back right away as some messages they handle may have a higher priority then my request for data. I am just trying to get a feel for the timing constraints for worst case data aquisition. Based on krmeds replay it would appear I am well within the capabilities of Windows.
Thanks
|
|
|
|
|
jonsey29847 wrote: Yes...Windows.
So which is it? Windows is not a RTOS, thus it cannot do anything every two microseconds.
Rather than polling, why don't you let the serial port tell you when it has data?
"Normal is getting dressed in clothes that you buy for work and driving through traffic in a car that you are still paying for, in order to get to the job you need to pay for the clothes and the car and the house you leave vacant all day so you can afford to live in it." - Ellen Goodman
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
|
|
|
|
|
My application is to communicate with an ECU (OBDII controller), the ECU is real time.
The controller has to be polled to get the data, my attachment point is a network (CAN) thus any data I see may be for other devices on the network.
|
|
|
|
|
Hello everyone,
Opaque pointer must be a pointer points to inner (hidden to outside) struct or class?
(refer to the C++ part)
http://en.wikipedia.org/wiki/Opaque_pointer
thanks in advance,
George
|
|
|
|
|
Interesting technique!
Maxwell Chen
|
|
|
|
|
Thanks Maxwell,
Any answers to my original question?
regards,
George
|
|
|
|
|
You have seen the C++ sample code on Wikipedia page.
As we know that if you declare an object member (as sample below):
class Object
{
};
class User
{
Object obj;
}; If you change anything to class Object's definition, the compiler recompiles class User (regarding to compilation unit), too.
But if you change into the below, it won't need to recompile class User.
class User
{
class Object;
Object* pObj;
};
class User::Object
{
};
Maxwell Chen
|
|
|
|
|
Thanks Maxwell!
My question is whether the wrapped pointer member must be pointing to inner structs/classes? Or the pointer could be pointed to global/namespace level structs/classes?
regards,
George
|
|
|
|
|
George_George wrote: whether the wrapped pointer member must be pointing to inner structs/classes? Or the pointer could be pointed to global/namespace level structs/classes?
Regarding to this term "opaque pointer", I think so. As wikipedia says it is to hide the internal implementations. If it were the below model, it wouldn't be something to hide.
class Object;
class User
{
Object* pObj;
};
class Object
{
};
Maxwell Chen
|
|
|
|
|
Thanks for sharing your points, Maxwell!
regards,
George
|
|
|
|
|
It may point to anything. Inner or outer, it's a bad practice. It's highly recommended not to use it.
OK,. what country just started work for the day ? The ASP.NET forum is flooded with retarded questions. -Christian Graus
Best wishes to Rexx[^]
|
|
|
|
|
VuNic wrote: It may point to anything. Inner or outer, it's a bad practice. It's highly recommended not to use it.
See this article for detailed descriptions: Compilation Firewalls[^].
Maxwell Chen
|
|
|
|
|
Thanks Maxwell,
Good link, I will study it.
regards,
George
|
|
|
|
|
That deals with just one case. But the article has not talked about the dangerous side of it. If you are have hard pointers like that, there's heck a lot of chances that you'll end up in memory leaks. If the program is 21 odd lines, then there's no problem. But in an application that has 40-50 thousand lines, if you are implementing hard pointers like this, that's it. It's an assured dissaster. I guess opaque pointers fit more better for the raw C guys and not C++. I'll give a little example here:
<br />
class MyApp<br />
{<br />
<br />
MyGun* pmygun;<br />
MyBomb* pBomb;<br />
MyMissle* pMissile;<br />
.<br />
.<br />
.<br />
<br />
}<br />
MyApp()<br />
{<br />
}<br />
<br />
LoadWeapon(Handle,Type)<br />
{<br />
}<br />
<br />
UnloadWeapon(Handle,Type)<br />
{<br />
<br />
}<br />
<br />
<br />
~MyApp()<br />
{<br />
}<br />
And sometime back my mate had such a pointer(pobj) in his MyAppclass, and in the destructor he kept calling pobj->release() without checking if it's been initialized or not. In most of the circumstances it got initialized and it went fine, but a tricky flow got thru these initializing conditions and when the destructor of the MyApp class got called, it crashed the application. This is just one example . I've seen a lot more like that.
I wish to suggest something called the smart-pointers.
OK,. what country just started work for the day ? The ASP.NET forum is flooded with retarded questions. -Christian Graus
Best wishes to Rexx[^]
|
|
|
|
|
Thanks VuNic,
The issues you described above are the common issues with raw pointers, are there any special new issues you described above special for opaque pointers?
regards,
George
|
|
|
|
|
But I think it's basic responsibility to check validity of pointers before using them to do release job.
~Foo() {
if(m_pG) {
m_pG->Release();
m_pG = NULL;
}
}
Maxwell Chen
|
|
|
|
|
Thanks VuNic,
Bad practice you mean pointing to outer or using opaque pointer?
regards,
George
|
|
|
|
|
See HERE[^].
Maxwell Chen
|
|
|
|
|
Hi Maxwell,
How do you pronounce the word "Pimpl"?
regards,
George
|
|
|
|
|
George_George wrote: How do you pronounce the word "Pimpl"?
I don't know. But "PIMPL" is a widely seen term in C++. You can google with this keyword "PIMPL".
(No 'e' at the tail.)
Maxwell Chen
|
|
|
|