you could try this
setserial /dev/ttyS0 spd_hi
or substitute one of the other options for spd_hi
Code:
spd_hi use 56kb instead of 38.4kb
spd_vhi use 115kb instead of 38.4kb
spd_shi use 230kb instead of 38.4kb
spd_warp use 460kb instead of 38.4kb
spd_cust use the custom divisor to set the speed at 38.4kb
(baud rate = baud_base / custom_divisor)
spd_normal use 38.4kb when a buad rate of 38.4kb is selected