I am writing a device driver where I need to read and write to a lot of registers. Is there any way I can tell if the operation as been successful? Currently we have a driver for some old HW but all of the driver functions are void and we just assume the operation was successful.
Are there any known tips or design patterns which would be good to follow when making a device driver?
Thanks,
You could do any of the following which suits you :
1) just write the register and immediately read back the same register.
2) create a function which outputs the value of each register when called.
Just make sure some registers might reset when read from it ( This might cause your code to malfunction )
Related
I've been trying to find a solution to get amazon-freertos to detect WIFI network down so I can reconnect. I have to say I am still not fully in understanding of how it all should work.
From reading up it looks like the intended way is to wait for callback to vApplicationIPNetworkEventHook where the programmer should implement necessary reconnects. However the problem is that this callback function does not get called for network down events, it only get called for network up events.
Reading FreeRTOS guide I see that for vApplicationIPNetworkEventHook to get a callback for network down event the underlying driver must first tell the TCPIP stack of this event, and it goes on to say not all drivers implement this, so I think I have located the problem now.
My question is how should the driver inform the TCPIP stack? The driver logs the network down event (it doesn't do much more than that) so I can add some code there to alert the TCPIP stack, but how should that be done? I cannot find any instructions for how to make this change, any help or suggestion is much appreciated.
amazon-freertos: https://github.com/MicrochipTech/amazon-freertos
MCU Test Board: Microchip curiosity_pic32mzw1
To add I think this should be the place (iot_wifi.c) to implement it:
WIFIReturnCode_t WIFI_RegisterNetworkStateChangeEventCallback( IotNetworkStateChangeEventCallback_t xCallback )
{
/** Needs to implement dispatching network state change events **/
return eWiFiNotSupported;
}
The question is just how.
Thanks,
Marcus
You can add a call to vApplicationIPNetworkEventHook() using eNetworkDown as the parameter.
I using freertos on my project. My code is stuck in hardfault handler, I want know last executed function address or last executed line address for debugging.How to debug code when PC is pointing Hardfault handler.
That information is 100% dependent on which microcontroller you are using, and also which tool chain you are using as some IDEs will do this for you. You failed to provide either piece of information, so are asking people to guess on your behalf. A good question is one that cannot only possibly be answered by another question.
I am going to guess you are using a Cortex-M microcontroller, in which case information on debugging a hard fault can be found on lots of links found by Google, including the following: http://www.freertos.org/Debugging-Hard-Faults-On-Cortex-M-Microcontrollers.html
This question already has an answer here:
How are data breakpoints created?
(1 answer)
Closed 1 year ago.
Requirements:
I need to generate an interrupt, when a memory location changes or is written to. From an ISR, I can trigger a blue screen which gives me a nice stack trace with method names.
Approaches:
Testing the value in the timer ISR. Obviously this doesn't give satisfying results.
I discovered the bochs virtual machine. It has a basic builtin debugger that can set data breakpoints and stop the program. But I can't seem to generate an interrupt at that point.
bochs allows one to connect a gdb to it. I haven't been able to build it with gdb support though.
Other thoughts:
A kind of "preview instruction" interrupt that triggers for every instruction before executing it. The set of used memory-writing instructions should be pretty manageable, but it would still be a PITA to extract the adress I think. And I think there is no such interrupt.
A kind of "preview memory access" interrupt. Again, I don't think its there.
Abuse paging. Mark the page of interest as not present and test the address in the page fault handler. One would still have to distinguish read and write operations and I think, the page fault handler doesn't get to know the exact address, just the page number.
See chapter 16 in Intel's Software Developer's Manual Volume 3A. It gives information about using the debug registers, which provide support for causing the debugger exception when accessing a certain address, among other things. The interrupt will be triggered after the instruction which caused it. Specifically, you will have to set one of dr0-dr3 to the address you want to watch, and dr7 with the proper values to tell the processor what types of accesses should cause the interrupt.
The reason I ask this is widows do not support a good method to communicate between processes. So I want to create a DLL for a communications point between windows processes. A thread is owned by a process and cannot be given to another process.
Each thread has a stack of its own.
If a DLL is loaded (loadlibray) and a DLL function is called that asks windows for memory. Am I write to think the thread is still being owned by the same process and allocates memory into that same process.
So I’m thinking can I turn to assembly to reallocate a small memory block to another process. Create a critical section, copy the data over to another (already created) memory block and return to the original block to its original process with out up setting windows. Has any one done that before. Or is thier a better way.
Best regards,
Lex Dean.
I see other methods that mite be quite fast but I would like a very fast method that has little over head. Pipes and internet will obviously work but are not the best option yet simple to implement (thanks to offer such suggestions guys). I want to send quite a few 500 byte blocks at quite regular intervals sometimes. I like WM_COPYDATA because it looks fast, my biggest question that I have been looking all over the internet is:- GetCurrentProcess and DuplicateHandle to get the real handle. Finding the other process. And using messages to set up memory and then use WM_COPYDATA. I only need two messages a) the pointer and size b) the data has been copied.
I get my application process easy ‘GetCurrentProcess’ except it’s a pseudo handle, that’s always $FFFFFFE. I need the real process handle and no body on the internet gives an example of DuplicateHandle. That’s what’s got me stumped. Can you show me an example of DuplicateHandle as that’s what’s got me stumped?
I do not like turning to a form to get a handle as one application dose not always have a current form.
I do not like turning to a form to get a handle as one application dose not always have a current form.
In Delphi I have seen message sending with TSpeedButton to set up a simple fast communication methods between applications that most probably uses about 80 instructions I guess. And so I still thinking to think dll’s. The example Mads Elvheim sent is on that same line as what I already know.
I'm still willing to understand any other options of using my own *.Dll
Because my applications important to me can simply register/unregister on the *.DLL its own process rather than searching all the time to see if a process is current.
It’s how I manage memory with a *.DLL between process but I’m not told about.
To me DLL’s are not hard to implement to me as I already have one of my own in operation.
The real bottom line is access to windows to create a good option. As I’m very open to idea’s. Even the assembly instructions for between processes or a windows call. But I do not what to get court crashing windows ether by doing things illegal.
So please show an example of what you have done that is to my needs. That is fast and I’m interested as I most probably will use it anyway.
I have a very fast IPC (interprocess communication) solution based on named pipes. It is very fast and very easy to use (It hides the actual implementation from you. You just work with data packets). Also tested and proven. You can find the code and the demo here.
http://www.cromis.net/blog/downloads/cromis-ipc/
It also works across computers in the same LAN.
If your processes have message loops (with windows), you can send/receive serialized data with the WM_COPYDATA message: http://msdn.microsoft.com/en-us/library/ms649011(VS.85).aspx
Just remember that only the allocated memory for the COPYDATASTRUCT::lpData member is allowed to be read. Again, you can not pass a structure that has pointers. The data must be serialized instead. And the receiving side can only read this structure, it can not write to it. Example:
/* Both are conceptual windows procedures. */
/* For sending : */
{
...
TCHAR msg[] = _T("This is a test\r\n");
HWND target;
COPYDATASTRUCT cd = {0};
cd.lpData = _tcsdup(msg); // We allocate and copy a string, which is fine.
cd.cbData = _tcsclen(msg) + 1; //The size of our data. Windows needs to know this.
target = FindWindow(..); //or EnumProcesses
SendMessage(target, WM_COPYDATA, (LPARAM)hwnd, (WPARAM)&cd);
}
/* For receiving */
{
...
case WM_COPYDATA:
{
TCHAR* msg;
COPYDATASTRUCT* cb = (COPYDATASTRUCT*)wParam;
sender = FindWindow(..); //or EnumProcesses
//check if this message is sent from the window/process we want
if(sender == (HWND)lParam){
msg = _tcsdup(cb->ldData);
...
}
break;
}
}
Otherwise, use memory mapped files, or network sockets.
I currently use Mailslots in Delphi to do it and it is very efficient.
"Win32 DLLs are mapped into the address space of the calling process. By default, each process using a DLL has its own instance of all the DLLs global and static variables. If your DLL needs to share data with other instances of it loaded by other applications, you can use either of the following approaches:
•Create named data sections using the data_seg pragma.
•Use memory mapped files. See the Win32 documentation about memory mapped files."
http://msdn.microsoft.com/en-us/library/h90dkhs0(VS.80).aspx
You cannot share pointers between processes, they only make sense to the process that alloc'd it. You're likely to run into issues.
Win32 is not different from any other modern OS in this aspect. There are plenty IPC services at your disposal in Windows.
Try to describe, which task you want to solve - not the "...then I think that I need to copy that block of memory here...". It's not your task. Your customer didn't say you: "I want to transfer thread from one process to another".
I created a class that handles serial port asynchronously. I use it to communicate with a modem. I have no idea why, but sometimes, when I close my application, I get the Blue Screen and my computer restarts. I logged my code step by step, but when the BSOD appeared, and my computer restarted, the file into which I was logging data contained only white spaces. Therefore I have no idea, what the reason of the BSOD could be.
I looked through my code carefully and I found several possible reasons of the problem (I was looking for all that could lead to accessing unallocated memory and causing AV exceptions).
When I rethought the idea of asynchronous operations, a few things came to my mind. Please verify whether these are right:
1) WaitCommEvent() takes a pointer to the overlapped structure. Therefore, if I call WaitCommEvent() inside a function and then leave the function, the overlapped structure cannot be a local variable, right? The event mask variable and event handle too, right?
2) ReadFile() and WriteFile() also take references or pointers to variables. Therefore all these variables have to be accessible until the overlapped read or write operations finish, right?
3) I call WaitCommEvent() only once and check for its result in a loop, in the mean time doing other things. Because I have no idea how to terminate asynchronous operations (is it possible?), when I destroy my class that keeps a handle to a serial port, I first close the handle, and then wait for the event in the overlapped structure that was used when calling the WaitCommEvent() function. I do this to be sure that the thread that waits asynchronously for a comm event does not access any fields of my class which is destroyed. Is it a good idea or is it stupid?
try
CloseHandle(FSerialPortHandle);
if Assigned(FWaitCommEvent) then
FWaitCommEvent.WaitFor(INFINITE);
finally
FSerialPortHandle := INVALID_HANDLE_VALUE;
FreeAndNil(FWaitCommEvent);
end;
Before I noticed all these, most of the variables mentioned in point one and two were local variables of the functions that called the three methods above. Could it be the reason of the BSOD or should I look for some other mistakes in my code?
When I corrected the code, the BSOD stopped occuring, but It might be a coincidence. How do you think?
Any ideas will be appreciated. Thanks in advance.
I read the CancelIo() function documentation and it states that this method cancells all I/O operations issued by the calling thread. Is it OK to wait for the FWaitCommEvent after calling CancelIo() if I know that WaitCommEvent() was issued by a different thread than the one that calls CancelIo()?
if Assigned(FWaitCommEvent) and CancelIo(FSerialPortHandle) then
begin
FWaitCommEvent.WaitFor(INFINITE);
FreeAndNil(FWaitCommEvent);
end;
I checked what happens in such case and the thread calling this piece of code didn't get deadlocked even though it did not issue WaitCommEvent(). I tested in on Windows 7 (if it matters). May I leave the code as is or is it dangerous? Maybe I misunderstood the documentation and this is the reason of my question. I apologize for asking so many questions, but I really need to be sure about that.
Thanks.
An application running as a standard user should never be able to cause a bug check (a.k.a. BSOD). (And an application running as an Administrator should have to go well out of its way to do so.) Either you ran into a driver bug or you have bad hardware.
By default, Windows is configured to save a minidump in %SystemRoot%\minidump whenever a bug check occurs. You may be able to determine more information about the crash by loading the minidump file in WinDbg, configuring WinDbg to use the Microsoft public symbol store, and running the !analyze -v command in WinDbg. At the very least, this should identify what driver is probably at fault (though I would guess it's your modem driver).
Yes, you do need to keep the TOverlapped structure available for the duration of the overlapped operation. You're going to call GetOverlappedResult at some point, and GetOverlappedResult says it should receive a pointer to a structure that was used when starting the overlapped operation. The event mask and handle can be stored in local variables if you want; you're going to have a copy of them in the TOverlapped structure anyway.
Yes, the buffers that ReadFile and WriteFile use must remain valid. They do not make their own local copies to use internally. The documentation for ReadFile even says so:
This buffer must remain valid for the duration of the read operation. The caller must not use this buffer until the read operation is completed.
If you weren't obeying that rule, then you were likely reading into unreserved stack space, which could easily cause all sorts of unexpected behavior.
To cancel an overlapped I/O operation, use CancelIo. It's essential that you not free the memory of your TOverlapped record until you're sure the associated operation has terminated. Likewise for the buffer you're reading or writing. CancelIo does not cancel the operation immediately, so your buffers might still be in use even after you call it.