ESRC_SET_VFI
ESRC_SET_VFI(freq >> 15));
eap1371_src_write(sc, ESRC_DAC1+ESRC_IREGS, ESRC_SET_VFI(16));
eap1371_src_write(sc, ESRC_DAC2+ESRC_IREGS, ESRC_SET_VFI(16));