Function in bash that generates random chars from /dev/random

In my .bashrc file I appended the line psswd() { LC_ALL=C tr -dc 'a-zA-Z0-9-!"@/#$%^&*()_+~' < /dev/urandom | head -c "$1";echo ;} so that when I type psswd n in the terminal, it returns a string of n random characters. I would like to achieve the same but using /dev/random instead of /dev/urandom. However when I replace /urandom by /random, calling psswd does nothing (cannot even output a single random character after 1 hour), it's as if it's frozen. I don't know why it is so, and I know it's not a problem of not having enough entropy. The reason is that the command od -An -N1 -i /dev/random returns a random number.

Note that this last command returns a random number almost instantly if I type it say after a fresh reboot. But if I have invoked a call to psswd n with /random, then the command returns a random number after about 15 seconds. So the call to /random seems to have some effect on /dev/random even though it produces no output when I call the function psswd.

Overall I'd like to know how I could create a function that uses /dev/random to generate a random string of n characters.