I'm using a AT32UC3B0256 microcontroller in combination with AVR32Studio 2.6 and I wouuld like to please a constant variable at a fixed address (
e.g. at position 0x80799999) at the end of the flash.
const int variable __attribute__((section(????))) = 1234;
Any ideas?
In Program use
const int variable __attribute__((section(".varaddress"))) = 1234;
and in your linker script add this flag:
-wl,--section-start=.varaddress=0x80799999
Also you can check Memory Sections in AVR
Related
Is it possible to access a PIC register by address?
Why I'd want to do that? because I need to compute it beforehand (for ports). If a function receives PORTX, it can figure out TRISX, LATX and ANSELX by adding an offset.
The include files use the __at macro to define registers
extern volatile PORTAbits_t PORTAbits __at(0x00C);
#define __at(x) __attribute__((address(x)))
I'm assuming __attribute__ and address are compiler specific?
Can I use that with memory map to access the computed address?
I managed to get it working (at least for what I want to achieve) by using pointers and offsets.
As an example PIC12F1571, has:
PORTA # 0x00C
TRISA # 0x08C
ANSELA # 0x18C
To set the port to digital output:
volatile unsigned char *direction = &PORTA + 0x080;
volatile unsigned char *mode = &PORTA + 0x180;
*mode = 0;
*direction = 0;
I am in 4-day fight with this code:
unsigned long baudrate = 0;
unsigned char databits = 0;
unsigned char stop_bits = 0;
char parity_text[10];
char flowctrl_text[4];
const char xformat[] = "%lu,%hhu,%hhu,%[^,],%[^,]\n";
const char xtext[] = "115200,8,1,EVEN,NFC\n";
int res = sscanf(xtext, xformat, &baudrate, &databits, &stop_bits, (char*) &parity_text, (char*) &flowctrl_text);
printf("Res: %d\r\n", res);
printf("baudrate: %lu, databits: %hhu, stop: %hhu, \r\n", baudrate, databits, stop_bits);
printf("parity: %s \r\n", parity_text);
printf("flowctrl: %s \r\n", flowctrl_text);
It returns:
Res: 5
baudrate: 115200, databits: 0, stop: 1,
parity:
flowctrl: NFC
Databits and parity missing !
Actually memory under the parity variable is '\0'VEN'\0',
looks like the first characters was somehow overwritten by sscanf procedure.
Return value of sscanf is 5, which suggests, that it was able to parse the input.
My configuration:
gccarmnoneeabi 7.2.1
Visual Studio Code 1.43.2
PlatformIO Core 4.3.1
PlatformIO Home 3.1.1
Lib ST-STM 6.0.0 (Mbed 5.14.1)
STM32F446RE (Nucleo-F446RE)
I have tried (without success):
compiling with mbed RTOS and without
variable types uint8_t, uint32_t
gccarm versions: 6.3.1, 8.3.1, 9.2.1
using another IDE (CLion+PlatformIO)
compiling on another computer (same config)
What actually helps:
making the variables static
compiling in Mbed online compiler
The behavior of sscanf is as whole very unpredictable, mixing the order or datatype of variables sometimes helps, but most often ends with another flaws in the output.
This took me longer than I care to admit. But like most issues it ended up being very simple.
char parity_text[10];
char flowctrl_text[4];
Needs to be changed to:
char parity_text[10] = {0};
char flowctrl_text[5] = {0};
The flowctrl_text array is not large enough at size four to hold "EVEN" and the NULL termination. If you bump it to a size of 5 you should have no problem. Just to be safe I would also initialize the arrays to 0.
Once I increased the size I had 0 issues with your existing code. Let me know if this helps.
I am planning to use kthread_run API in my kernel module.
As kthread_run, returns a struct task_struct *, which i want to store in a variable global across my module.
However, i want one thread each for a cpu and i obtain no of cpus using num_online_cpus.
However, when i write following code:
//outside init_module function
int cpus = num_online_cpus();
static struct task_struct *my_tasks[cpus];
static int __init init_module(){
for(int j = 0; j < cpus; ++j){
my_tasks[j] = kthread_run(...);
}
}
However, i get following error on this:
error: variably modified ‘tasks’ at file scope
How can i achieve this ???
If your variables are actually one per cpu, you might want to use the per_cpu macros. The gist is, you declare such a variable with:
DEFINE_PER_CPU(struct task_struct, my_tasks);
and then access the variable using
get_cpu_var(my_tasks).foo = bar;
You can get more info at See http://www.makelinux.net/ldd3/chp-8-sect-5 (or percpu.h) for more details.
AMD OpenCL Programming Guide, Section 6.3 Constant Memory Optimization:
Globally scoped constant arrays. These arrays are initialized,
globally scoped, and in the constant address space (as specified in
section 6.5.3 of the OpenCL specification). If the size of an array is
below 64 kB, it is placed in hardware constant buffers; otherwise, it
uses global memory. An example of this is a lookup table for math
functions.
I want to use this "globally scoped constant array". I have such code in pure C
#define SIZE 101
int *reciprocal_table;
int reciprocal(int number){
return reciprocal_table[number];
}
void kernel(int *output)
{
for(int i=0; i < SIZE; i+)
output[i] = reciprocal(i);
}
I want to port it into OpenCL
__kernel void kernel(__global int *output){
int gid = get_global_id(0);
output[gid] = reciprocal(gid);
}
int reciprocal(int number){
return reciprocal_table[number];
}
What should I do with global variable reciprocal_table? If I try to add __global or __constant to it I get an error:
global variable must be declared in addrSpace constant
I don't want to pass __constant int *reciprocal_table from kernel to reciprocal. Is it possible to initialize global variable somehow? I know that I can write it down into code, but does other way exist?
P.S. I'm using AMD OpenCL
UPD Above code is just an example. I have real much more complex code with a lot of functions. So I want to make array in program scope to use it in all functions.
UPD2 Changed example code and added citation from Programming Guide
#define SIZE 2
int constant array[SIZE] = {0, 1};
kernel void
foo (global int* input,
global int* output)
{
const uint id = get_global_id (0);
output[id] = input[id] + array[id];
}
I can get the above to compile with Intel as well as AMD. It also works without the initialization of the array but then you would not know what's in the array and since it's in the constant address space, you could not assign any values.
Program global variables have to be in the __constant address space, as stated by section 6.5.3 in the standard.
UPDATE Now, that I fully understood the question:
One thing that worked for me is to define the array in the constant space and then overwrite it by passing a kernel parameter constant int* array which overwrites the array.
That produced correct results only on the GPU Device. The AMD CPU Device and the Intel CPU Device did not overwrite the arrays address. It also is probably not compliant to the standard.
Here's how it looks:
#define SIZE 2
int constant foo[SIZE] = {100, 100};
int
baz (int i)
{
return foo[i];
}
kernel void
bar (global int* input,
global int* output,
constant int* foo)
{
const uint id = get_global_id (0);
output[id] = input[id] + baz (id);
}
For input = {2, 3} and foo = {0, 1} this produces {2, 4} on my HD 7850 Device (Ubuntu 12.10, Catalyst 9.0.2). But on the CPU I get {102, 103} with either OCL Implementation (AMD, Intel). So I can not stress, how much I personally would NOT do this, because it's only a matter of time, before this breaks.
Another way to achieve this is would be to compute .h files with the host during runtime with the definition of the array (or predefine them) and pass them to the kernel upon compilation via a compiler option. This, of course, requires recompilation of the clProgram/clKernel for every different LUT.
I struggled to get this work in my own program some time ago.
I did not find any way to initialize a constant or global scope array from the host via some clEnqueueWriteBuffer or so. The only way is to write it explicitely in your .cl source file.
So here my trick to initialize it from the host is to use the fact that you are actually compiling your source from the host, which also means you can alter your src.cl file before compiling it.
First my src.cl file reads:
__constant double lookup[SIZE] = { LOOKUP }; // precomputed table (in constant memory).
double func(int idx) {
return(lookup[idx])
}
__kernel void ker1(__global double *in, __global double *out)
{
... do something ...
double t = func(i)
...
}
notice the lookup table is initialized with LOOKUP.
Then, in the host program, before compiling your OpenCL code:
compute the values of my lookup table in host_values[]
on your host, run something like:
char *buf = (char*) malloc( 10000 );
int count = sprintf(buf, "#define LOOKUP "); // actual source generation !
for (int i=0;i<SIZE;i++) count += sprintf(buf+count, "%g, ",host_values[i]);
count += sprintf(buf+count,"\n");
then read the content of your source file src.cl and place it right at buf+count.
you now have a source file with an explicitely defined lookup table that you just computed from the host.
compile your buffer with something like clCreateProgramWithSource(context, 1, (const char **) &buf, &src_sz, err);
voilà !
It looks like "array" is a look-up table of sorts. You'll need to clCreateBuffer and clEnqueueWriteBuffer so the GPU has a copy of it to use.
I am using MPLABx and the HI Tech PICC compiler. My target chip is a PIC16F876. By looking at the pic16f876.h include file, it appears that it should be possible to set the system registers of the chip by referring to them by name.
For example, within the CCP1CON register, bits 0 to 3 set how the CCP and PWM modules work. By looking at the pic16f876.h file, it looks like it should be possible to refer to these 4 bits alone, without change the value of the rest of the CCP1CON register.
However, I have tried to refer to these 4 bits in a variety of ways with no success.
I have tried;
CCP1CON.CCP1M=0xC0; this results in "error: struct/union required
CCP1CON:CCP1M=0xC0; this results in "error: undefined identifier "CCP1M"
but both have failed. I have read through the Hi Tech PICC compiler manual, but cannot see how to do this.
From the pic16f876.h file, it looks to me as though I should be able to refer to these subsets within the system registers by name, as they are defined in the .h file.
Does anyone know how to accomplish this?
Excerpt from pic16f876.h
// Register: CCP1CON
volatile unsigned char CCP1CON # 0x017;
// bit and bitfield definitions
volatile bit CCP1Y # ((unsigned)&CCP1CON*8)+4;
volatile bit CCP1X # ((unsigned)&CCP1CON*8)+5;
volatile bit CCP1M0 # ((unsigned)&CCP1CON*8)+0;
volatile bit CCP1M1 # ((unsigned)&CCP1CON*8)+1;
volatile bit CCP1M2 # ((unsigned)&CCP1CON*8)+2;
volatile bit CCP1M3 # ((unsigned)&CCP1CON*8)+3;
#ifndef _LIB_BUILD
volatile union {
struct {
unsigned CCP1M : 4;
unsigned CCP1Y : 1;
unsigned CCP1X : 1;
};
struct {
unsigned CCP1M0 : 1;
unsigned CCP1M1 : 1;
unsigned CCP1M2 : 1;
unsigned CCP1M3 : 1;
};
} CCP1CONbits # 0x017;
#endif
You need to access the bitfield members through an instance of a struct. In this case, that is CCP1CONbits. Because it is a bitfield, you only need to have the number of significant bits as defined in the bitfield, not the full eight bits in your code.
So:
CCP1CONbits.CCP1M = 0x0c;
Should be the equivalent of what you are trying to do. If you want to set all eight bits at once you can use CCP1CON = 0xc0. That would set the CCP1M bits to 0x0c and all the other bits to zero.
The header you gave also has individual bit symbols, so you could do this too:
CCP1M0 = 1;
CCP1M1 = 1;
CCP1M2 = 0;
CCP1M3 = 0;
Although the bitfield approach is cleaner.