Implement PD 3.0 collision avoidance

It's pretty easy to implement, it turns out!  A new event gets sent to
the protocol TX thread when the PE is starting an AMS.  Just before the
message is transmitted, the TX thread checks if that event was received,
and if it was, it waits for the Type-C Current to look like 3.0 A
(SinkTxOk) before proceeding.  Now, to the best of my knowledge, we're
actually doing Power Delivery 3.0 as correctly as we ever did Power
Delivery 2.0, which is to say, everything is right except we don't do
BIST.

lib/docs/firmware_structure.svg

@@ -363,9 +363,9 @@
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      inkscape:pageshadow="2"
-     inkscape:zoom="3.959798"
-     inkscape:cx="149.55024"
-     inkscape:cy="821.73649"
+     inkscape:zoom="5.6"
+     inkscape:cx="193.2269"
+     inkscape:cy="800.04611"
      inkscape:document-units="mm"
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      showgrid="true"
@@ -957,5 +957,16 @@
          x="85.978149"
          id="tspan5148"
          sodipodi:role="line">PPS_REQUEST</tspan></text>
+    <text
+       id="text972"
+       y="91.465988"
+       x="82.486923"
+       style="font-style:normal;font-weight:normal;font-size:2.11666656px;line-height:3.30729151px;font-family:sans-serif;text-align:end;letter-spacing:0px;word-spacing:0px;text-anchor:end;fill:#000000;fill-opacity:1;stroke:none;stroke-width:0.13229166px;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1"
+       xml:space="preserve"><tspan
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:1.76388884px;font-family:'Source Code Pro';-inkscape-font-specification:'Source Code Pro';text-align:end;text-anchor:end;stroke-width:0.13229166px"
+         y="91.465988"
+         x="82.486923"
+         id="tspan970"
+         sodipodi:role="line">START_AMS</tspan></text>
   </g>
 </svg>

lib/include/pdb_fusb.h

@@ -45,7 +45,9 @@ enum fusb_typec_current {
     fusb_tcc_none = 0,
     fusb_tcc_default = 1,
     fusb_tcc_1_5 = 2,
-    fusb_tcc_3_0 = 3
+    fusb_sink_tx_ng = 2,
+    fusb_tcc_3_0 = 3,
+    fusb_sink_tx_ok = 3
 };
 
 

lib/src/policy_engine.c

@@ -350,6 +350,8 @@ static enum policy_engine_state pe_sink_ready(struct pdb_config *cfg)
 
     /* If the DPM wants us to, send a Get_Source_Cap message */
     if (evt & PDB_EVT_PE_GET_SOURCE_CAP) {
+        /* Tell the protocol layer we're starting an AMS */
+        chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_START_AMS);
         return PESinkGetSourceCap;
     }
 
@@ -363,11 +365,15 @@ static enum policy_engine_state pe_sink_ready(struct pdb_config *cfg)
             chPoolFree(&pdb_msg_pool, cfg->pe._message);
             cfg->pe._message = NULL;
         }
+        /* Tell the protocol layer we're starting an AMS */
+        chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_START_AMS);
         return PESinkEvalCap;
     }
 
     /* If SinkPPSPeriodicTimer ran out, send a new request */
     if (evt & PDB_EVT_PE_PPS_REQUEST) {
+        /* Tell the protocol layer we're starting an AMS */
+        chEvtSignal(cfg->prl.tx_thread, PDB_EVT_PRLTX_START_AMS);
         return PESinkSelectCap;
     }
 

lib/src/protocol_tx.c

@@ -131,6 +131,17 @@ static enum protocol_tx_state protocol_tx_construct_message(struct pdb_config *c
     cfg->prl._tx_message->hdr &= ~PD_HDR_MESSAGEID;
     cfg->prl._tx_message->hdr |= (cfg->prl._tx_messageidcounter % 8) << PD_HDR_MESSAGEID_SHIFT;
 
+    /* PD 3.0 collision avoidance */
+    if ((cfg->pe.hdr_template & PD_HDR_SPECREV) == PD_SPECREV_3_0) {
+        /* If we're starting an AMS, wait for permission to transmit */
+        evt = chEvtGetAndClearEvents(PDB_EVT_PRLTX_START_AMS);
+        if (evt & PDB_EVT_PRLTX_START_AMS) {
+            while (fusb_get_typec_current(&cfg->fusb) != fusb_sink_tx_ok) {
+                chThdSleepMilliseconds(1);
+            }
+        }
+    }
+
     /* Send the message to the PHY */
     fusb_send_message(&cfg->fusb, cfg->prl._tx_message);
 

lib/src/protocol_tx.h

@@ -32,6 +32,7 @@
 #define PDB_EVT_PRLTX_I_RETRYFAIL EVENT_MASK(2)
 #define PDB_EVT_PRLTX_DISCARD EVENT_MASK(3)
 #define PDB_EVT_PRLTX_MSG_TX EVENT_MASK(4)
+#define PDB_EVT_PRLTX_START_AMS EVENT_MASK(5)
 
 
 /*