New function nfc_idle() to set the NFC device in idle mode.

nfc_disconnect() now switch NFC device into idle before disconnecting;
pn53x_data now have a operating_mode enum to know the current running mode (initiator, target or idle);
new pn53x_PowerDown wrapper for PowerDown (PN532) command;

Note: ARYGON idle mode now to be implemented and ACR122 does not support this mode.

libnfc/drivers/acr122.c

@@ -427,5 +427,6 @@ const struct nfc_driver_t acr122_driver = {
   .configure  = pn53x_configure,
 
   .abort_command  = NULL,
+  .idle  = NULL,
 };
 

libnfc/drivers/arygon.c

@@ -494,5 +494,7 @@ const struct nfc_driver_t arygon_driver = {
   .configure  = pn53x_configure,
 
   .abort_command  = arygon_abort_command,
+  // FIXME Implement me
+  .idle  = NULL,
 };
 

libnfc/drivers/pn532_uart.c

@@ -444,5 +444,6 @@ const struct nfc_driver_t pn532_uart_driver = {
   .configure  = pn53x_configure,
 
   .abort_command  = pn532_uart_abort_command,
+  .idle  = pn53x_idle,
 };
 

libnfc/drivers/pn53x_usb.c

@@ -341,16 +341,17 @@ error:
 void
 pn53x_usb_disconnect (nfc_device_t * pnd)
 {
-  int     res;
-
   pn53x_usb_ack (pnd);
 
+  pn53x_idle (pnd);
+
   if (DRIVER_DATA (pnd)->model == ASK_LOGO) {
     /* Set P30, P31, P32, P33, P35 to logic 1 and P34 to 0 logic */
     /* ie. Switch all LEDs off and turn off progressive field */
     pn53x_write_register (pnd, SFR_P3, 0xFF, _BV (P30) | _BV (P31) | _BV (P32) | _BV (P33) | _BV (P35));
   }
 
+  int res;
   if ((res = usb_release_interface (DRIVER_DATA (pnd)->pudh, 0)) < 0) {
     ERR ("usb_release_interface failed (%i)", res);
   }
@@ -654,4 +655,5 @@ const struct nfc_driver_t pn53x_usb_driver = {
   .configure  = pn53x_usb_configure,
 
   .abort_command  = pn53x_usb_abort_command,
+  .idle  = pn53x_idle,
 };