c64x+ SYS/BIOS Hwi doesn't work until trigged manually

Hi, I'm trying to implement a hardware interrupt application with SYS/BIOS. I'm using DSK6455 kit. I want to read data from McBSP1 upon rx interrupt . This is how I create Hwi instance:

    Hwi_Params params0;

    // Initialize the error block
    Error_init(&eb);

    // Initialize the Hwi parameters
    Hwi_Params_init(&params0);

    // Set the GEM event id in the params
    params0.eventId = 42;

    // create the Hwi for the specified interrupt number and params
    rx_hwi = Hwi_create(10, codec_rx_isr, &params0, &eb);

This doesn't work unless I trigger interrupt manually. After triggering interrupt manually once it continues without problem. Adding this line:

   Hwi_post(10);

to above code looks like to solve my problem. But I want to know what I'm missing ??

Notes:

I'm using board support library's functions (DSK6455_init,DSK6455_AIC23_openCodec) to init McBSP module.

CCS is v5.3, SYS/BIOS 6.34.2.18