Using Serial and one softwareserial works perfectly well so far. I only run into troubles when I use 2 softwareSerials at the same time. With your AltSoftSerial I'd also read from Serial and write on SoftwareSerial?
Here a sketch that works perfectly well but uses the hardware UART-pins so when the USB-Mini is connected, then it reads/writes there...
#include <SoftwareSerial.h>
//Software-UART Pins for XBee SX 868
SoftwareSerial xbee_serial(4, 5); // RX, TX
void setup() {
Serial.begin(9600);
while (!Serial) {
;
}
xbee_serial.begin(9600);
}
void loop() {
//Input, which comes via USB-Mini is transfered to SWSerial
if (Serial.available()) {
xbee_serial.write(Serial.read());
}
//Input, which comes via SWSerial is transfered to USB-Mini
if (xbee_serial.available()) {
Serial.write(xbee_serial.read());
}
}