glReadPixels failed use FBO on Mali-T628

I want to i to implement offescreen render in my project with FBO;It works on Other manufacturers‘ GPU,but get glReadPixels error 502 on  Mali-T628.I am very confused. Then I try to directly glReadPixels without FBO,no error happened,but i get a white screen.Could any one know this problem？

here is my code to readpixel

 getbuffer(uint8_t *dst_buf)

{

    int framesize=g_width * g_height * 4;

   glBindFramebuffer( GL_FRAMEBUFFER, g_framebuffer );

   checkGlError( "glBindFramebuffer" );

    GLenum status = glCheckFramebufferStatus( GL_FRAMEBUFFER );

    checkGlError( "glCheckFramebufferStatus" );

    switch( status ){

        case GL_FRAMEBUFFER_COMPLETE:

            log_debug("FBO good %d",status);

            break;

        case GL_FRAMEBUFFER_UNSUPPORTED:

            log_debug("FBO wrong %d",status);

            break;

        default:

            break;

    }

    glReadBuffer(GL_COLOR_ATTACHMENT0);

    if( g_asyncReadingIndex == 0 ){

        g_asyncReadingIndex = 1;

        g_asyncCopyingIndex = 0;

    }

    else{

        g_asyncReadingIndex = 0;

        g_asyncCopyingIndex = 1;

    }

    glBindBuffer( GL_PIXEL_PACK_BUFFER, g_pboID[g_asyncReadingIndex] );

    checkGlError( "glBindBuffer" );

    glFinish();

    checkGlError( "glFinish" );

    pj_get_timestamp(&ts_begin);

    glReadPixels( 0, 0,g_width,g_height, GL_RGBA, GL_UNSIGNED_BYTE, 0);

    checkGlError( "glReadPixels" );

    glBindBuffer( GL_PIXEL_PACK_BUFFER, g_pboID[g_asyncCopyingIndex] );

    checkGlError( "glBindBuffer" );

    GLubyte* bufferData = NULL;

    bufferData = (GLubyte*)glMapBufferRange( GL_PIXEL_PACK_BUFFER,0,

                                             framesize, GL_MAP_READ_BIT );

    checkGlError( "glMapBufferRange" );

    if( bufferData != NULL ){

        memcpy(dst_buf, bufferData, framesize);

        glUnmapBuffer( GL_PIXEL_PACK_BUFFER )；

        checkGlError( "glUnmapBuffer" );

    }

    glBindBuffer( GL_PIXEL_PACK_BUFFER, 0 );

    checkGlError( "glBindBuffer" );

    glBindFramebuffer( GL_FRAMEBUFFER, 0 );

    checkGlError( "glBindFramebuffer");

}