Added "identify" command

The GUI will have a button to identify a particular PD Buddy Sink, in
case several are connected to the computer at once.  The button will
cause the LED to blink quickly for a couple seconds, then go back to
normal.  To allow this, I added a new LED blink mode (FAST_BLINK_SLOW)
that causes 8 fast blinks, then returns to SLOW_BLINK mode.  A new
"identify" command triggers this LED mode.

src/led.c

 #define LED_MEDIUM MS2ST(250)
 #define LED_SLOW MS2ST(500)
 
-/* Number of blinks for medium blink off mode */
+/* Number of blinks for temporary modes */
 #define LED_MEDIUM_BLINKS 3
+#define LED_FAST_BLINKS 8
 
 
 thread_t *pdb_led_thread;
                     palToggleLine(LINE_LED);
                 }
                 break;
+            case PDB_EVT_LED_FAST_BLINK_SLOW:
+                timeout = LED_FAST;
+                if (i == 0) {
+                    palSetLine(LINE_LED);
+                } else if (i < (LED_FAST_BLINKS * 2)) {
+                    palToggleLine(LINE_LED);
+                } else {
+                    palClearLine(LINE_LED);
+                    timeout = TIME_INFINITE;
+                    chEvtSignal(pdb_led_thread, PDB_EVT_LED_SLOW_BLINK);
+                }
+                break;
             default:
                 break;
         }

src/led.h

 #define PDB_EVT_LED_FAST_BLINK EVENT_MASK(2)
 #define PDB_EVT_LED_MEDIUM_BLINK_OFF EVENT_MASK(3)
 #define PDB_EVT_LED_SLOW_BLINK EVENT_MASK(4)
+#define PDB_EVT_LED_FAST_BLINK_SLOW EVENT_MASK(5)
 
 /* The LED thread object */
 extern thread_t *pdb_led_thread;

src/shell.c

 
 #include "usbcfg.h"
 #include "storage.h"
+#include "led.h"
 
 
 /* Buffer for unwritten configuration */
 {
     (void) argv;
     if (argc > 0) {
-        chprintf(chp, "Usage: get_tmpcfg [index]\r\n");
+        chprintf(chp, "Usage: get_tmpcfg\r\n");
         return;
     }
 
     }
 }
 
+static void cmd_identify(BaseSequentialStream *chp, int argc, char *argv[])
+{
+    (void) chp;
+    (void) argv;
+    if (argc > 0) {
+        chprintf(chp, "Usage: identify\r\n");
+        return;
+    }
+
+    chEvtSignal(pdb_led_thread, PDB_EVT_LED_FAST_BLINK_SLOW);
+}
+
 static const struct pdb_shell_cmd commands[] = {
     {"erase", cmd_erase, "Erase all stored configuration"},
     {"write", cmd_write, "Write the changes to flash"},
     {"set_v", cmd_set_v, "Set the voltage in millivolts"},
     {"set_i", cmd_set_i, "Set the current in milliamps"},
     /* TODO {"set_v_range", cmd_set_v_range, "Set the minimum and maximum voltage in millivolts"},*/
+    {"identify", cmd_identify, "Blink the LED to identify the device"},
     {NULL, NULL, NULL}
 };