Simple memcpy not working

Hello all,

I am trying to do a simple memcpy with Cuda 1.1 on a Windows XP machine with a GeForce 8600 GTS board. I am compiling under MS Visual Studio 2005 and I have used the template application for a test.

Here is the code for the host:

/* [2007.12.29 Phil Pratt-Szeliga] : CUDA */

#include <cutil.h>

#include ""

double tilted_angle[513] = {0.0};

main (int argc, char *argv[])




	dim3  grid( 1, 1, 1);

	dim3  threads( 1, 1, 1);

	double *d_tilted_angle;

	CUDA_SAFE_CALL( cudaMalloc( (void**) &d_tilted_angle, sizeof(tilted_angle)));

	CUDA_SAFE_CALL( cudaMemcpy( d_tilted_angle, tilted_angle, sizeof(tilted_angle),cudaMemcpyHostToDevice) );

	slice_kernel<<<grid, threads>>>(d_tilted_angle);

	CUT_CHECK_ERROR("Kernel execution failed");


	CUT_CHECK_ERROR("Kernel execution failed");

	//copy the memory back

	CUDA_SAFE_CALL( cudaMemcpy( tilted_angle, d_tilted_angle, sizeof(tilted_angle),cudaMemcpyDeviceToHost) );

	//free the allocated memory



And here is the code for the device:



#include <stdio.h>

__global__ void slice_kernel(double * tilted_angle)


	for(int i = 0; i < 513; i++){

  tilted_angle[i] = 15.5;




#endif // #ifndef _TEMPLATE_KERNEL_H_

Here is my problem: (In Debug mode) Before I call the cudaMemcpy (device to host) tilted_angle on the host is all zeros. After I call cudaMemcpy tilted_angle takes on values like: 5.426734841397e-315#DEN

However, in EmuDebug mode tilted_angle takes on values like 15.5 in main.

Does anyone know what is going on?



You are using doubles, the current GPU generation is single-precision only.
The current CUDA compiler will squash doubles to floats. Convert the array before sending to the GPU.

Okay thanks

Is double supported on host functions? Where is the documentation related to this?

host code is compiled by your host compiler, so yes. I believe it is in the programming manual, or otherwise the documentation of nvcc