Aligning equations in a system of equations with inside arrows

I wrote the code:

begin{empheq}[left=empheqlbrace]{align*}
text{Risorsa occupata $quad Leftrightarrow$} quad s &= 0 
text{Risorsa libera $quad Leftrightarrows$} quad s &= 1
end{empheq}

but Texmaker gives me an error. If I rewrite it as follows:

begin{empheq}[left=empheqlbrace]{align*}
text{Risorsa occupata $quad Leftrightarrow$} quad s &= 0 
quad s &= 1
end{empheq}

it works. How can I fix this error?

documentclass{article}
usepackage{amsmath}
begin{document}
[
begin{cases} 
text{Risorsa occupata} & Leftrightarrow  s = 0 
text{Risorsa libera}   & Leftrightarrow  s = 1
end{cases} 
]
end{document}