Update requested power after writing configuration

The PD Buddy Sink now requests new power after configuration is written.
This means that in Setup mode, the voltage and current can be
re-negotiated on the fly.  Cool, huh?

It's still impossible to turn the output on and off from the shell.  New
commands will allow that soon enough, though.  Also, I'm seeing some
weird behavior when switching to/from 5 V (power shuts off entirely
sometimes), but I suspect that's a quirk of the source I'm using (Asus
USB 3.1 UPD Panel) and not the PD Buddy Sink itself.  I plan to make or
buy a USB power/data splitter to verify this.

src/policy_engine.c

     /* Wait for an event */
     if (min_power) {
         evt = chEvtWaitAnyTimeout(PDB_EVT_PE_MSG_RX | PDB_EVT_PE_RESET
-                | PDB_EVT_PE_I_OVRTEMP, PD_T_SINK_REQUEST);
+                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP,
+                PD_T_SINK_REQUEST);
     } else {
         evt = chEvtWaitAny(PDB_EVT_PE_MSG_RX | PDB_EVT_PE_RESET
-                | PDB_EVT_PE_I_OVRTEMP);
+                | PDB_EVT_PE_I_OVRTEMP | PDB_EVT_PE_GET_SOURCE_CAP);
     }
 
     /* If we got reset signaling, transition to default */
         return PESinkHardReset;
     }
 
+    /* If the DPM wants us to, send a Get_Source_Cap message */
+    if (evt & PDB_EVT_PE_GET_SOURCE_CAP) {
+        return PESinkGetSourceCap;
+    }
+
     /* If no event was received, the timer ran out. */
     if (evt == 0) {
         /* Repeat our Request message */
 
 static enum policy_engine_state pe_sink_get_source_cap(void)
 {
-    /* Stubbed until we actually have a need for this */
+    /* Get a message object */
+    union pd_msg *get_source_cap = chPoolAlloc(&pdb_msg_pool);
+    /* Make a Get_Source_Cap message */
+    get_source_cap->hdr = PD_MSGTYPE_GET_SOURCE_CAP | PD_DATAROLE_UFP
+        | PD_SPECREV_2_0 | PD_POWERROLE_SINK | PD_NUMOBJ(0);
+    /* Transmit the Get_Source_Cap */
+    chMBPost(&pdb_prltx_mailbox, (msg_t) get_source_cap, TIME_IMMEDIATE);
+    chEvtSignal(pdb_prltx_thread, PDB_EVT_PRLTX_MSG_TX);
+    eventmask_t evt = chEvtWaitAny(PDB_EVT_PE_TX_DONE | PDB_EVT_PE_TX_ERR
+            | PDB_EVT_PE_RESET);
+    /* Free the sent message */
+    chPoolFree(&pdb_msg_pool, get_source_cap);
+    get_source_cap = NULL;
+    /* If we got reset signaling, transition to default */
+    if (evt & PDB_EVT_PE_RESET) {
+        return PESinkTransitionDefault;
+    }
+    /* If the message transmission failed, send a hard reset */
+    if ((evt & PDB_EVT_PE_TX_DONE) == 0) {
+        return PESinkHardReset;
+    }
+
     return PESinkReady;
 }
 

src/policy_engine.h

 #define PDB_EVT_PE_TX_ERR EVENT_MASK(3)
 #define PDB_EVT_PE_HARD_SENT EVENT_MASK(4)
 #define PDB_EVT_PE_I_OVRTEMP EVENT_MASK(5)
+#define PDB_EVT_PE_GET_SOURCE_CAP EVENT_MASK(6)
 
 /* The Policy Engine thread object */
 extern thread_t *pdb_pe_thread;

src/shell.c

 #include "usbcfg.h"
 #include "storage.h"
 #include "led.h"
+#include "policy_engine.h"
 #include "pd.h"
 
 
     }
 
     pdb_config_flash_update(&tmpcfg);
+
+    chEvtSignal(pdb_pe_thread, PDB_EVT_PE_GET_SOURCE_CAP);
 }
 
 static void cmd_load(BaseSequentialStream *chp, int argc, char *argv[])