Wow this is a quick answer !
I'm 100% sure it use com3 and 4, but thank's for the hint , my irq setting were wrong. (they were set in my software to irq5 and irq9 )
Also , Iâ€™ve been told it use to work only on a certain type of serial card, This card is using a 16c650 uart. From the datasheet this uart is using a 32 byte Fifo, compare to the more common 16c550 16 byte fifo , maybe this can have and impact ? Do you think your code is easily modifiable for this ? I still havenâ€™t been able to compile the hole project on my own , but if you think it feasible I'll try harder.
I've no experience watsoever in C except in the microcontrolers world