ios - Mobile Website - Viewport depending on device-width -

i have mobile website , little problem viewport meta tag in -part.

my code:

<meta id="testviewport" name="viewport" content="width=640"> 

it working fine on iphone 4s on ipad 2, doesn't work properly. want viewport set width of users hardware. there way achieve or have read out model type , set viewport switch or if code?

thanks in advance.

niels

edit:

here's css. want achieve: let site displayed in device-width. if display-size smaller 640px, should change viewport 640px. not working on ios 7.0, safari:

@viewport {      width: device-width;     } @media screen , (max-device-width: 640px) {    @viewport {      width: 640px;    } } 

edit#2:

fixed using js in of index.html:

<meta id="viewport" name="viewport" content="width=device-width" /> <script>     if (window.innerwidth < 640){     var vp = document.getelementbyid('viewport');     vp.setattribute('content', 'width=640');     } </script> 

instead of setting content="width=640" try 1 <meta name="viewport" content="width=device-width">

update:

to serve high-res images / change zooming retina devices css use this:

@media  (-webkit-min-device-pixel-ratio: 2),  (min-resolution: 192dpi) {      /* retina-specific stuff here */ }