My application running on a Cortex M4 is crashing with a hard fault. The CSFR register indicates IMPRECISERR.
Reading http://chmorgan.blogspot.nl/2013/06/debugging-imprecise-bus-access-fault-on.html I am advised to set the DISDEFWBUF bit in the Auxiliary Control Register (ACTLR). This will allow me to get PRECISERR which are easier to debug.
By reading the programming manual
for our CPU, we can see the ACTLR is at address 0xE000 E008, and the DISDEFWBUF bit is 1.
In main, this bit can be set with the following code:
*(uint8_t *)0xE000E008 |= (1<<i);
Where i = 1;
Change the value in SFRs pallete. STM32f429,Register:
Read this article for more information.
Related
I try to control USB camera with libuvc on Ubuntu 20.04.
when the ctrl value = 0x400 and the unit value = 0x200,
I can call uvc_set_ctrl(device_handle, 0x4, 0x2, output_buffer, buffer_length), and it's successful to set value to specify register.
But how can I offer value to uvc_set_ctrl() when the unit value = 0x303?
These are library-specific functions -- different implementations of UVC (for example on Windows) won't have these, so I think your question would be better suited to the libuvc forum.
For what it's worth, I tried looking at the libuvc documentation to read about uvc_set_ctrl, but the URL for the documentation on the README page isn't valid anymore: https://int80k.com/libuvc/doc/
I am a newbie to RISC-V. I wonder how I could get FLOPS using SW or HW method. I try to use CSR to get FLOPS, but there are some problems.
As I know, if I redesign the hpmcounter which counts every floating operation event, I could get FLOPS by using the csr read instruction. I know there is a similar design in the rocket-chip-based SiFive's U54-core manual. In the manual I can see SiFive core has sophisticated feature counting capabilities. This feature is controlled by the mhpmevent CSR. If I set lower eight bits of mhpmevent as 0, and enable the [19-25] bit, I can get counter value from mhpmcounter. I actually want to design this field like SiFive core.
I try to imitate it for FLOPS, but I encounter some problems.
I can't access to the mhpmcounter, and I can see the illegal instruction error like following link.
illegal instruction error message!!
I make a simple test code and compile it successfully, but there is a illegal instruction error when I implement it using spike and cycle accurate emulator. Both use proxy kernel.
// simple test code
unsigned long instret1 = 0;
unsigned long instret2 = 0;
float a,b,c;
a = 5.0;
b = 4.0;
asm volatile ("csrrs %0, mhpmcounter3, x0 " : "=r"(instret1));
c = a + b;
asm volatile ("csrrs %0, mhpmcounter3, x0 " : "=r"(instret2));
printf("instruction count : %ul \n", instret2-instret1);
It is hard to change to M-mode from user mode for access to the mhpmevet and mhpmcounter. In the RISC-V priv-spec 1.10, I find xRET instruction can change mode. Following text is about xRET in the spec.
The MRET, SRET, or URET instructions are used to return from traps in M-mode, S-mode, or
U-mode respectively. When executing an xRET instruction, supposing xPP holds the value y, x IE
is set to x PIE; the privilege mode is changed to y; x PIE is set to 1; and xPP is set to U (or M if
user-mode is not supported).
If someone knows it, I hope to see the detailed assembly code.
I try to modify rocket-chip/src/main/scala/rocket/CSR.scala for redesign CSR. Is it the only way? Firstly, I want to use spike to test the counter value. How should I change the code?
If anybody has some other ideas or has accomplished it, please point to me. Thanks!
I am trying to make a small kernel for 80386 processor mainly for learning purpose and want to get the full memory map of the available RAM.
I have read that it is possible and better to do so with the help of GRUB than directly querying the BIOS.
Can anybody tell me how do I do it ?
Particularly, for using bios functionality in real mode we use bios interrupts and get the desired values in some registers , what is the actual equivalent way when we want to use GRUB provided functions ?
Here is the process I use in my kernel (note that this is 32bit). In my bootstrap assembly file, I tell GRUB to provide me with a memory map:
.set MEMINFO, 1 << 1 # Get memory map from GRUB
Then, GRUB loads the address of the multiboot info structure into ebx for you (this structure contains the address of the memory map). Then I call into C code to handle the actual iteration and processing of the memory map. I do something like this to iterate over the map:
/* Macro to get next entry in memory map */
#define MMAP_NEXT(m) \
(multiboot_memory_map_t*)((uint32_t)m + m->size + sizeof(uint32_t))
void read_mmap(multiboot_info_t* mbt){
multiboot_memory_map_t* mmap = (multiboot_memory_map_t*) mbt->mmap_addr;
/* Iterate over memory map */
while((uint32_t)mmap < mbt->mmap_addr + mbt->mmap_length) {
// process the current memory map entry
mmap = MMAP_NEXT(mmap);
}
}
where multiboot_info_t and multiboot_memory_map_t are defined as in the Gnu multiboot.h file. As Andrew Medico posted in the comments, here is a great link for getting started with this.
I am triying to create a code emmiter in c++ in order to learn how to make an emulator, but im having a hard time making dynamic assembler work:
unsigned char program[] = {0x90, 0x90, 0xC3 }; //nop; nop; ret
void (*p)(void) = (void(*)()) &program;
p();
always return access violation .....
im working with visual studio 2012 C++ win32 console application
Thanks.
After some research I found this:
you have to allocate the memory and change the read/write/execution permissions to: Allow Read, Disallow Write, Allow Execution.
See this question for a "how to do it".
On Windows the function is VirtualProtect, you'll want to pass in PAGE_EXECUTE_READWRITE to get execute permission.
By default Windows does not allow memory execution. It's called Data Execute Prevention (DEP).
And for linux:
See mprotect(). Once you have filled a (n-)page-sized memory region (allocated with mmap()) with code, change its permissions to disallow writes and allow execution.
another fix for your issue on windows is just add your program to DEP whitelist... (You probbly didn't notice, but your crash is probably of type BEX, BEX crashes are in 99% cases related to DEP)
P.S. When you create a working code emitter.. mind giving me a copy? xD
I have a program that is creating a map file, its able to do that call just fine, m_hMap = CreateFileMapping(m_hFile,0,dwProtect,0,m_dwMapSize,NULL);, but when the subsequent function call to MapViewOfFile(m_hMap,dwViewAccess,0,0,0), I get an error code of 8, which is ERROR_NOT_ENOUGH_MEMORY, or error string "error Not enough storage is available to process this command".
So I'm not totally understanding what the MapViewOfFile does for me, and how to fix the situation.
some numbers...
m_dwMapSize = 453427200
dwProtect = PAGE_READWRITE;
dwViewAccess = FILE_MAP_ALL_ACCESS;
I think my page size is 65536
In case of very large file and to read it, it is recommended to read it in small pieces and then process each piece. And MapViewOfFile function is used to map a piece in memory.
Look at http://msdn.microsoft.com/en-us/library/windows/desktop/aa366761(v=vs.85).aspx need offset to do its job properly i.e. in case you want to read a very large file in pieces. Mostly due to fragmentation and related reason very large memory request fails.
If you are working on a 64 bit processor then the system will allocate a total of 4GB memory with bit set LargeaddressAware.
go to Configuration properties->linker->system. in Enable largeaddressware: check
Yes /LARGEADDRESSAWARE and check.