These functions are declared in the coresrv/io/ports.h file.
rtl_uint8_t IoReadIoPort8(rtl_size_t port);
rtl_uint16_t IoReadIoPort16(rtl_size_t port);
rtl_uint32_t IoReadIoPort32(rtl_size_t port);
These functions read one, two, or four bytes, respectively, from the specified port and return the read value.