J6 entry:how to create mipmap for compressed texture with opengles

I have a PVR file whic has 512*512 size I create it with pvrtextool ,and I upload to my J6 entry board GPU as texture using glcompressedtexImg2D, However now I want to create mipmap for this texture, I know that I cannot create mipmap for it automatically using glgeneratemipmap since it is compressed ,I have to upload it manually level by level.I do like the following:

///parse PVR
 
FILE* m_pFile;
 
unsigned char* m_pData =NULL;
 
int nChannel;
 
EN_FMT_COLOR emFlag;
 
int nPicWid;
 
int nPicHgt;
 
int nSize;
 
int nLevel;
 
 
  
 m_pFile = fopen("./Blue512.pvr", "rb");
             
 fseek(m_pFile, 0, SEEK_END);
      
 int nFileLen = ftell(m_pFile);
       
if(nFileLen < 52)
       
{
            return 0;
        }

              
m_pData = new unsigned char[nFileLen];
       
memset(m_pData, 0, nFileLen);
  
      
 rewind(m_pFile);
          
 int nError = fread(m_pData,1,nFileLen,m_pFile);       
  if (m_pData[0] != 'P' || m_pData[1] != 'V' || m_pData[2] != 'R')
     
  {
           
     return 0;
       
   }

              
int nFormat = *(int*)(m_pData +8);
 
 emFlag   = HIK3D_FMT_RGBA_4BPP;
     
     
 nPicWid = *(int*)(m_pData +24);
       
nPicHgt = *(int*)(m_pData +28);
       
int nOffcet = *(int*)(m_pData +48);
       
nLevel = *(int*)(m_pData +44);
      
 m_pData += nOffcet + 52;
       
nSize    = nFileLen - nOffcet - 52;
       
RUN_INFO("size is %d\r\n",nSize);
  
int* pnLevelSize;
       
unsigned char* pCurrentPos = m_pData;

      
 pnLevelSize = new int[nLevel];

       
int nWidth  = nPicWid;
       
int nHeight = nPicHgt;
       
float bpp = 0.5f;
       
     
for(int i = 0; i < nLevel; i++)
       
{
           
    pnLevelSize[i]= nWidth * nHeight * bpp;
   
if(pnLevelSize[i] < 32)
   
{
    
  pnLevelSize[i] = 32;
   
}
      
   
 nWidth  = max(1,nWidth/2 );
           
nHeight = max(1,nHeight/2 );
      
 }
      
  
 
 
  glGenTextures(1, &m_nTexture);
  
 printf("gen 1 tex %d\r\n", m_nTexture);
 
  glBindTexture(GL_TEXTURE_2D, m_nTexture);
  
  
GLenum p;
  
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
  
GLenum internalformat;
 
internalformat = GL_COMPRESSED_RGBA_PVRTC_4BPPV1_IMG;
 
nWidth  = nPicWid;
       
nHeight = nPicHgt;

  
for (int i=0; i < nLevel; i++)
  
{
       
glCompressedTexImage2D(GL_TEXTURE_2D, i, internalformat, nWidth, nHeight, 0 , pnLevelSize[i], (void*)pCurrentPos);
 pCurrentPos = pCurrentPos + pnLevelSize[i];  
    
nWidth  = max(8,nWidth/2 );
   
nHeight = max(8,nHeight/2);
 
}
   
glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
   
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  
  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

I notice I cannot upload texture level which width is less than 8 if so I get error from glgeterror, so I make all levels that width less than 8 same size as the one with 8 as width. this texture is totally black if I choose GL_LINEAR_MIPMAP_NEAREST as GL_TEXTURE_MIN_FILTER ,it is correct if I set it to GL_LINEAR. I think there is something wrong with the way I create mipmap ,could anyone give me some advice? Thanks a lot.