Problem while using Timer interrupts and I2C in Xmega128A1

[haribabu413]

Hi i am working on design of digital musical instruments like tanpura,Tabala etc. i am getting one problem while using the timer interrupts and I2C in one of my instrument. In my project i am having kepad to change settings , I2C LCD for displaying Menu of Instrument like Volume, Tone, Tempo etc. here i am reading the samples of sound file (Sound of Tanpura)from external memory in timer interrupts configured in compare match A Low level interrupt and using I2C (in PortD without interrupt) for interfacing LCD to display menu. When display of menu will changes during change of settings that time the playing of sound getting interrupting. If i disable the I2C its playing properly even when i change the settings. I am getting the problem only when i enable the I2C for displaying menu in LCD other wise everything thing works fine.. except reading of sound file remaining all function are in main only. i am not getting why the timer interrupt getting interrupted while calling LCD display function it should not happened as interrupt having highest priority than the I2C(without using interrupt).

In I2C i am checking the Write interrupt Flag to know whether Byte is transferred or not. I want to know one thing here is I2C handled by CPU or it will done by separate hardware in the controller like DMA. Please tell me any one where is the problem.. why the sound getting interrupted when i call I2C for LCD display.