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I.MX6 : Using USB OTG without dynamic VBUS pin ?

Question asked by Frederic COIFFIER on Jan 26, 2015
Latest reply on Jan 28, 2015 by Wigros Sun

On our design based in i.MX6Q, we're using USB OTG (as host or as device). On this design, we have a OTG ID pin on i.MX6 (GPIO1) but no dynamic VBUS pin : this one is set to +5V.


With our previous Linux kernel (3.0.35), it wasn't a problem. But with the new 3.10.31, it seems that the USB ChipIdea driver monitors the changes of VBUS pin in the OTG stage machine :


} else if (otg_int_src & OTGSC_AVVIS) {
  hw_write_otgsc(ci, OTGSC_AVVIS, OTGSC_AVVIS);
  if (otgsc & OTGSC_AVV) {
    fsm->a_vbus_vld = 1;
  } else {
    fsm->a_vbus_vld = 0;
    fsm->b_conn = 0;


With this kernel, the USB device is disconnected few milliseconds after detecting it, as the condition 'fsm->a_vbus_vld = 1' cannot be generated as there is no change on VBUS.


So is there a way to get a working OTG with VBUS pin connected to +5V ?


I made this workaround in ci_hdrc_otg_fsm_init() :

ci->fsm.a_vbus_vld = hw_read_otgsc(ci, OTGSC_AVV) ? 1 : 0;

So like this, 'fsm->a_vbus_vld' reflects the correct state of VBUS.