Added output command

Just as specified last night.  This represents the completion of a big
part of the new interactive Power Delivery features of the shell.
Next up: printing the source's advertised PDOs.

src/device_policy_manager.c

 #include "fusb302b.h"
 
 
+bool pdb_dpm_output_enabled = true;
+
 bool pdb_dpm_led_pd_status = true;
 
 bool pdb_dpm_usb_comms = false;
     dpm_present_voltage = dpm_requested_voltage;
 
     /* Set the power output */
-    if (state) {
+    if (state && pdb_dpm_output_enabled) {
         /* Turn the output on */
         if (pdb_dpm_led_pd_status) {
             chEvtSignal(pdb_led_thread, PDB_EVT_LED_OUTPUT_ON);

src/device_policy_manager.h

 #include "messages.h"
 
 
+/* Whether the DPM is able to turn on the output */
+extern bool pdb_dpm_output_enabled;
+
 /* Whether the DPM sets the LED to indicate the PD status */
 extern bool pdb_dpm_led_pd_status;
 

src/main.c

 static void setup(void)
 {
     /* Configure the DPM to play nice with the shell */
+    pdb_dpm_output_enabled = false;
     pdb_dpm_led_pd_status = false;
     pdb_dpm_usb_comms = true;
 

src/shell.c

 #include "usbcfg.h"
 #include "storage.h"
 #include "led.h"
+#include "device_policy_manager.h"
 #include "policy_engine.h"
 #include "pd.h"
 
     chEvtSignal(pdb_led_thread, PDB_EVT_LED_IDENTIFY);
 }
 
+static void cmd_output(BaseSequentialStream *chp, int argc, char *argv[])
+{
+    if (argc == 0) {
+        /* With no arguments, print the output status */
+        if (pdb_dpm_output_enabled) {
+            chprintf(chp, "enabled\r\n");
+        } else {
+            chprintf(chp, "disabled\r\n");
+        }
+    } else if (argc == 1) {
+        /* Set the output status and re-negotiate power */
+        if (strcmp(argv[0], "enable") == 0) {
+            pdb_dpm_output_enabled = true;
+            chEvtSignal(pdb_pe_thread, PDB_EVT_PE_GET_SOURCE_CAP);
+        } else if (strcmp(argv[0], "disable") == 0) {
+            pdb_dpm_output_enabled = false;
+            chEvtSignal(pdb_pe_thread, PDB_EVT_PE_GET_SOURCE_CAP);
+        } else {
+            /* Or, if the argument was invalid, print a usage message */
+            chprintf(chp, "Usage: output [enable|disable]\r\n");
+        }
+    } else {
+        /* If there are too many arguments, print a usage message */
+        chprintf(chp, "Usage: output [enable|disable]\r\n");
+    }
+}
+
 /*
  * List of shell commands
  */
     {"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"},
+    {"output", cmd_output, "Get or set the output status"},
     {NULL, NULL, NULL}
 };