AC97_GENERAL_PURPOSE_REGISTER
ac_wr(ac, AC97_GENERAL_PURPOSE_REGISTER, 0);
v = SHADOW(ac, AC97_GENERAL_PURPOSE_REGISTER);
ac_wr(ac, AC97_GENERAL_PURPOSE_REGISTER, v);
ac_clr(ac, AC97_GENERAL_PURPOSE_REGISTER, GPR_MS_MIC2);
ac_set(ac, AC97_GENERAL_PURPOSE_REGISTER, GPR_MS_MIC2);
ac_clr(ac, AC97_GENERAL_PURPOSE_REGISTER, GPR_MS_MIC2);