[Android] Per-pixel-Specular disappeared when target SM 2.0

Hi there,
I have a shader which uses per-pixel-specular and worked fine when target SM 3.0, but the specular will disappear if change shade model to 2.0, could any one here please tell me what's going on? how can i stick with SM 2.0 while still have the per-pixel-specular effects? thank you.

 

Problem solved :

Code (CSharp):

1. struct v2f
2. {
3.     float4  pos     : SV_POSITION;
4.     float2  uv      : TEXCOORD0;
5.     fixed3  viewDir : COLOR;
6. };

It turns out that the out type of viewDir is the problem, just change it from 'COLOR' to 'TEXCOORD1" will work fine in SM 2.0.

Thank you.