Index: uspace/drv/bus/usb/ohci/endpoint_list.c
===================================================================
--- uspace/drv/bus/usb/ohci/endpoint_list.c	(revision 721d4b6e1ee228e501502436aef92929f3c14463)
+++ uspace/drv/bus/usb/ohci/endpoint_list.c	(revision 9515f674f1653460bfb4650aefd98bd6c414bd1b)
@@ -60,5 +60,5 @@
 	    name, instance->list_head, instance->list_head_pa);
 
-	ed_init(instance->list_head, NULL);
+	ed_init(instance->list_head, NULL, NULL);
 	list_initialize(&instance->endpoint_list);
 	fibril_mutex_initialize(&instance->guard);
Index: uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.c
===================================================================
--- uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.c	(revision 721d4b6e1ee228e501502436aef92929f3c14463)
+++ uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.c	(revision 9515f674f1653460bfb4650aefd98bd6c414bd1b)
@@ -34,31 +34,59 @@
 #include "endpoint_descriptor.h"
 
-static unsigned direc[3] =
-    { ED_STATUS_D_IN, ED_STATUS_D_OUT, ED_STATUS_D_TRANSFER };
+/** USB direction to OHCI values translation table. */
+static const uint32_t dir[] = {
+	[USB_DIRECTION_IN] = ED_STATUS_D_IN,
+	[USB_DIRECTION_OUT] = ED_STATUS_D_OUT,
+	[USB_DIRECTION_BOTH] = ED_STATUS_D_TD,
+};
 
-void ed_init(ed_t *instance, endpoint_t *ep)
+/**
+ * Initialize ED.
+ *
+ * @param instance ED structure to initialize.
+ * @param ep Driver endpoint to use.
+ * @param td TD to put in the list.
+ *
+ * If @param ep is NULL, dummy ED is initalized with only skip flag set.
+ */
+void ed_init(ed_t *instance, const endpoint_t *ep, const td_t *td)
 {
 	assert(instance);
 	bzero(instance, sizeof(ed_t));
+
 	if (ep == NULL) {
+		/* Mark as dead, used for dummy EDs at the beginning of
+		 * endpoint lists. */
 		instance->status = ED_STATUS_K_FLAG;
 		return;
 	}
-	assert(ep);
+	/* Non-dummy ED must have TD assigned */
+	assert(td);
+
+	/* Status: address, endpoint nr, direction mask and max packet size. */
 	instance->status = 0
 	    | ((ep->address & ED_STATUS_FA_MASK) << ED_STATUS_FA_SHIFT)
 	    | ((ep->endpoint & ED_STATUS_EN_MASK) << ED_STATUS_EN_SHIFT)
-	    | ((direc[ep->direction] & ED_STATUS_D_MASK) << ED_STATUS_D_SHIFT)
+	    | ((dir[ep->direction] & ED_STATUS_D_MASK) << ED_STATUS_D_SHIFT)
 	    | ((ep->max_packet_size & ED_STATUS_MPS_MASK)
 	        << ED_STATUS_MPS_SHIFT);
 
-
+	/* Low speed flag */
 	if (ep->speed == USB_SPEED_LOW)
 		instance->status |= ED_STATUS_S_FLAG;
+
+	/* Isochronous format flag */
 	if (ep->transfer_type == USB_TRANSFER_ISOCHRONOUS)
 		instance->status |= ED_STATUS_F_FLAG;
 
+	/* Set TD to the list */
+	const uintptr_t pa = addr_to_phys(td);
+	instance->td_head = pa & ED_TDHEAD_PTR_MASK;
+	instance->td_tail = pa & ED_TDTAIL_PTR_MASK;
+
+	/* Set toggle bit */
 	if (ep->toggle)
 		instance->td_head |= ED_TDHEAD_TOGGLE_CARRY;
+
 }
 /**
Index: uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.h
===================================================================
--- uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.h	(revision 721d4b6e1ee228e501502436aef92929f3c14463)
+++ uspace/drv/bus/usb/ohci/hw_struct/endpoint_descriptor.h	(revision 9515f674f1653460bfb4650aefd98bd6c414bd1b)
@@ -45,5 +45,14 @@
 #include "completion_codes.h"
 
+/**
+ * OHCI Endpoint Descriptor representation.
+ *
+ * See OHCI spec. Chapter 4.2, page 16 (pdf page 30) for details */
 typedef struct ed {
+	/**
+	 * Status field.
+	 *
+	 * See table 4-1, p. 17 OHCI spec (pdf page 31).
+	 */
 	volatile uint32_t status;
 #define ED_STATUS_FA_MASK (0x7f)   /* USB device address   */
@@ -51,20 +60,32 @@
 #define ED_STATUS_EN_MASK (0xf)    /* USB endpoint address */
 #define ED_STATUS_EN_SHIFT (7)
-#define ED_STATUS_D_MASK (0x3)     /* direction */
+#define ED_STATUS_D_MASK (0x3)     /* Direction */
 #define ED_STATUS_D_SHIFT (11)
 #define ED_STATUS_D_OUT (0x1)
 #define ED_STATUS_D_IN (0x2)
-#define ED_STATUS_D_TRANSFER (0x3)
+#define ED_STATUS_D_TD (0x3) /* Direction is specified by TD */
 
-#define ED_STATUS_S_FLAG (1 << 13) /* speed flag: 1 = low */
-#define ED_STATUS_K_FLAG (1 << 14) /* skip flag (no not execute this ED) */
-#define ED_STATUS_F_FLAG (1 << 15) /* format: 1 = isochronous*/
-#define ED_STATUS_MPS_MASK (0x3ff) /* max_packet_size*/
+#define ED_STATUS_S_FLAG (1 << 13) /* Speed flag: 1 = low */
+#define ED_STATUS_K_FLAG (1 << 14) /* Skip flag (no not execute this ED) */
+#define ED_STATUS_F_FLAG (1 << 15) /* Format: 1 = isochronous */
+#define ED_STATUS_MPS_MASK (0x3ff) /* Maximum packet size */
 #define ED_STATUS_MPS_SHIFT (16)
 
+	/**
+	 * Pointer to the last TD.
+	 *
+	 * OHCI hw never changes this field and uses it only for a reference.
+	 */
 	volatile uint32_t td_tail;
 #define ED_TDTAIL_PTR_MASK (0xfffffff0)
 #define ED_TDTAIL_PTR_SHIFT (0)
 
+	/**
+	 * Pointer to the first TD.
+	 *
+	 * Driver should not change this field if the ED is active.
+	 * This field is updated by OHCI hw and points to the next TD
+	 * to be executed.
+	 */
 	volatile uint32_t td_head;
 #define ED_TDHEAD_PTR_MASK (0xfffffff0)
@@ -75,4 +96,9 @@
 #define ED_TDHEAD_HALTED_FLAG (0x1)
 
+	/**
+	 * Pointer to the next ED.
+	 *
+	 * Driver should not change this field on active EDs.
+	 */
 	volatile uint32_t next;
 #define ED_NEXT_PTR_MASK (0xfffffff0)
@@ -80,33 +106,38 @@
 } __attribute__((packed)) ed_t;
 
-void ed_init(ed_t *instance, endpoint_t *ep);
+void ed_init(ed_t *instance, const endpoint_t *ep, const td_t *td);
 
-static inline void ed_set_td(ed_t *instance, td_t *td)
+/**
+ * Set the last element of TD list
+ * @param instance ED
+ * @param instance TD to set as the last item.
+ */
+static inline void ed_set_tail_td(ed_t *instance, const td_t *td)
 {
 	assert(instance);
-	uintptr_t pa = addr_to_phys(td);
-	instance->td_head =
-	    ((pa & ED_TDHEAD_PTR_MASK)
-	    | (instance->td_head & ~ED_TDHEAD_PTR_MASK));
+	const uintptr_t pa = addr_to_phys(td);
 	instance->td_tail = pa & ED_TDTAIL_PTR_MASK;
 }
 
-static inline void ed_set_end_td(ed_t *instance, td_t *td)
-{
-	assert(instance);
-	uintptr_t pa = addr_to_phys(td);
-	instance->td_tail = pa & ED_TDTAIL_PTR_MASK;
-}
-
-static inline void ed_append_ed(ed_t *instance, ed_t *next)
+/**
+ * Set next ED in ED chain.
+ * @param instance ED to modify
+ * @param next ED to append
+ */
+static inline void ed_append_ed(ed_t *instance, const ed_t *next)
 {
 	assert(instance);
 	assert(next);
-	uint32_t pa = addr_to_phys(next);
+	const uint32_t pa = addr_to_phys(next);
 	assert((pa & ED_NEXT_PTR_MASK) << ED_NEXT_PTR_SHIFT == pa);
 	instance->next = pa;
 }
 
-static inline int ed_toggle_get(ed_t *instance)
+/**
+ * Get toggle bit value stored in this ED
+ * @param instance ED
+ * @return Toggle bit value
+ */
+static inline int ed_toggle_get(const ed_t *instance)
 {
 	assert(instance);
@@ -114,12 +145,16 @@
 }
 
-static inline void ed_toggle_set(ed_t *instance, int toggle)
+/**
+ * Set toggle bit value stored in this ED
+ * @param instance ED
+ * @param toggle Toggle bit value
+ */
+static inline void ed_toggle_set(ed_t *instance, bool toggle)
 {
 	assert(instance);
-	assert(toggle == 0 || toggle == 1);
-	if (toggle == 1) {
+	if (toggle) {
 		instance->td_head |= ED_TDHEAD_TOGGLE_CARRY;
 	} else {
-		/* clear halted flag when reseting toggle */
+		/* Clear halted flag when reseting toggle TODO: Why? */
 		instance->td_head &= ~ED_TDHEAD_TOGGLE_CARRY;
 		instance->td_head &= ~ED_TDHEAD_HALTED_FLAG;
Index: uspace/drv/bus/usb/ohci/ohci_batch.c
===================================================================
--- uspace/drv/bus/usb/ohci/ohci_batch.c	(revision 721d4b6e1ee228e501502436aef92929f3c14463)
+++ uspace/drv/bus/usb/ohci/ohci_batch.c	(revision 9515f674f1653460bfb4650aefd98bd6c414bd1b)
@@ -217,5 +217,5 @@
 {
 	assert(ohci_batch);
-	ed_set_end_td(ohci_batch->ed, ohci_batch->tds[ohci_batch->td_count]);
+	ed_set_tail_td(ohci_batch->ed, ohci_batch->tds[ohci_batch->td_count]);
 }
 /*----------------------------------------------------------------------------*/
Index: uspace/drv/bus/usb/ohci/ohci_endpoint.c
===================================================================
--- uspace/drv/bus/usb/ohci/ohci_endpoint.c	(revision 721d4b6e1ee228e501502436aef92929f3c14463)
+++ uspace/drv/bus/usb/ohci/ohci_endpoint.c	(revision 9515f674f1653460bfb4650aefd98bd6c414bd1b)
@@ -102,6 +102,5 @@
 	}
 
-	ed_init(ohci_ep->ed, ep);
-	ed_set_td(ohci_ep->ed, ohci_ep->td);
+	ed_init(ohci_ep->ed, ep, ohci_ep->td);
 	endpoint_set_hc_data(
 	    ep, ohci_ep, ohci_endpoint_fini, ohci_ep_toggle_get, ohci_ep_toggle_set);