How to enable three uarts on 7688

For Developers
1 
# echo "000" >> ttyS0
# echo "000" >> console 
000
# echo "000" >> console 
000
# echo "000" >> console 
000
# echo "000" >> ttyS1  
000

console is ttyS1? /dev only has S0 and S1

console sometime output

[2020-09-24 02:31:37.496][RexHint]r
                                   N

                                   @@@@@@

how to change the console port?