u32                   control2_register;     /* cached value */
        u32                   creg_spdif;
        u32                   creg_spdif_stream;
+       int                   clock_source_locked;
        char                 *card_name;             /* digiface/multiface */
        HDSP_IO_Type          io_type;               /* ditto, but for code use */
         unsigned short        firmware_rev;
        return change;
 }
 
+static int snd_hdsp_info_clock_source_lock(snd_kcontrol_t *kcontrol, snd_ctl_elem_info_t * uinfo)
+{
+       uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
+       uinfo->count = 1;
+       uinfo->value.integer.min = 0;
+       uinfo->value.integer.max = 1;
+       return 0;
+}
+
+static int snd_hdsp_get_clock_source_lock(snd_kcontrol_t * kcontrol, snd_ctl_elem_value_t * ucontrol)
+{
+       hdsp_t *hdsp = snd_kcontrol_chip(kcontrol);
+       
+       ucontrol->value.integer.value[0] = hdsp->clock_source_locked;
+       return 0;
+}
+
+static int snd_hdsp_put_clock_source_lock(snd_kcontrol_t * kcontrol, snd_ctl_elem_value_t * ucontrol)
+{
+       hdsp_t *hdsp = snd_kcontrol_chip(kcontrol);
+       int change;
+
+       change = (int)ucontrol->value.integer.value[0] != hdsp->clock_source_locked;
+       if (change)
+               hdsp->clock_source_locked = ucontrol->value.integer.value[0];
+       return change;
+}
+
 #define HDSP_DA_GAIN(xname, xindex) \
 { .iface = SNDRV_CTL_ELEM_IFACE_HWDEP, \
   .name = xname, \
 HDSP_SPDIF_NON_AUDIO("IEC958 Non-audio Bit", 0),
 /* 'Sample Clock Source' complies with the alsa control naming scheme */ 
 HDSP_CLOCK_SOURCE("Sample Clock Source", 0),
+{
+       /* FIXME: should be PCM or MIXER? */
+       /* .iface = SNDRV_CTL_ELEM_IFACE_PCM, */
+       .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+       .name = "Sample Clock Source Locking",
+       .info = snd_hdsp_info_clock_source_lock,
+       .get = snd_hdsp_get_clock_source_lock,
+       .put = snd_hdsp_put_clock_source_lock,
+},
 HDSP_SYSTEM_CLOCK_MODE("System Clock Mode", 0),
 HDSP_PREF_SYNC_REF("Preferred Sync Reference", 0),
 HDSP_AUTOSYNC_REF("AutoSync Reference", 0),
        snd_iprintf (buffer, "System Clock Mode: %s\n", system_clock_mode);
 
        snd_iprintf (buffer, "System Clock Frequency: %d\n", hdsp->system_sample_rate);
+       snd_iprintf (buffer, "System Clock Locked: %s\n", hdsp->clock_source_locked ? "Yes" : "No");
                
        snd_iprintf(buffer, "\n");
 
         */
 
        spin_lock_irq(&hdsp->lock);
-       if ((err = hdsp_set_rate(hdsp, params_rate(params), 0)) < 0) {
-               spin_unlock_irq(&hdsp->lock);
-               _snd_pcm_hw_param_setempty(params, SNDRV_PCM_HW_PARAM_RATE);
-               return err;
-       } else {
-               spin_unlock_irq(&hdsp->lock);
+       if (! hdsp->clock_source_locked) {
+               if ((err = hdsp_set_rate(hdsp, params_rate(params), 0)) < 0) {
+                       spin_unlock_irq(&hdsp->lock);
+                       _snd_pcm_hw_param_setempty(params, SNDRV_PCM_HW_PARAM_RATE);
+                       return err;
+               }
        }
+       spin_unlock_irq(&hdsp->lock);
 
        if ((err = hdsp_set_interrupt_interval(hdsp, params_period_size(params))) < 0) {
                _snd_pcm_hw_param_setempty(params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
 
        snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
        snd_pcm_hw_constraint_list(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, &hdsp_hw_constraints_period_sizes);
-       if (hdsp->io_type == H9632) {
-               runtime->hw.channels_min = hdsp->qs_out_channels;
-               runtime->hw.channels_max = hdsp->ss_out_channels;
+       if (hdsp->clock_source_locked) {
+               runtime->hw.rate_min = runtime->hw.rate_max = hdsp->system_sample_rate;
+       } else if (hdsp->io_type == H9632) {
                runtime->hw.rate_max = 192000;
                runtime->hw.rates = SNDRV_PCM_RATE_KNOT;
                snd_pcm_hw_constraint_list(runtime, 0, SNDRV_PCM_HW_PARAM_RATE, &hdsp_hw_constraints_9632_sample_rates);
        }
+       if (hdsp->io_type == H9632) {
+               runtime->hw.channels_min = hdsp->qs_out_channels;
+               runtime->hw.channels_max = hdsp->ss_out_channels;
+       }       
        
        snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
                             snd_hdsp_hw_rule_out_channels, hdsp,