From the hardware point of view you need a IRDA transciever from for.ex. Avago, Vishay etc.
If your serial port isnt IRDA compatibel i.e. 3/16 encode/decode you can use a interface chip like Avago HSDL-7002 or Vishay TOIM4243
You can just use a modified version of a software UART to do the same job, but instead it toggles the TRIS of a hardware PWM pin on a micro controller...
Depending on the receiver, upto 1200 baud is no real issue. Not sure what the TRIS is referred too on an AVR, but for a PIC it’s the input/output control of a pin