From 50c8ef07b6c312248697abc37b5486ee2a147644 Mon Sep 17 00:00:00 2001
From: Jiaxun Yang <jiaxun.yang@flygoat.com>
Date: Tue, 18 Jun 2024 14:18:28 +0100
Subject: [PATCH] jtagremote: Implement ntrst pin

ntrst pin is critical to some JTAG taps to put tap
into a known state.

Implement it in jtagremote testbench with corresponding
remote bitbang commands and hook it up in litex_sim.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 .../sim/core/modules/jtagremote/jtagremote.c  | 41 +++++++++++++------
 litex/tools/litex_sim.py                      |  6 +--
 2 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/litex/build/sim/core/modules/jtagremote/jtagremote.c b/litex/build/sim/core/modules/jtagremote/jtagremote.c
index 1b0fa4e25..29b4df1e7 100644
--- a/litex/build/sim/core/modules/jtagremote/jtagremote.c
+++ b/litex/build/sim/core/modules/jtagremote/jtagremote.c
@@ -15,6 +15,7 @@ struct session_s {
 	char *tdo;
 	char *tck;
 	char *tms;
+	char *ntrst;
 	char *sys_clk;
 	struct event *ev;
 	char databuf[2048];
@@ -199,6 +200,7 @@ static int jtagremote_add_pads(void *sess, struct pad_list_s *plist)
     litex_sim_module_pads_get(pads, "tdi", (void**)&s->tdi);
     litex_sim_module_pads_get(pads, "tdo", (void**)&s->tdo);
     litex_sim_module_pads_get(pads, "tms", (void**)&s->tms);
+    litex_sim_module_pads_get(pads, "ntrst", (void**)&s->ntrst);
   }
 
   if(!strcmp(plist->name, "sys_clk"))
@@ -227,19 +229,34 @@ static int jtagremote_tick(void *sess, uint64_t time_ps)
   {
 	  c = s->databuf[s->data_start];
 
-	  if((c >= '0') && (c <= '7')){
-		  *s->tck = ((c - '0') >> 2) & 1;
-		  *s->tms = ((c - '0') >> 1) & 1;
-		  *s->tdi = (c - '0')  & 1;
-	  }
-	  if(c == 'R'){
-		  val = *s->tdo + '0';
-		  if(-1 == write(s->fd, &val, 1)) {
-			  eprintf("Error writing on socket\n");
-			  ret = RC_ERROR;
-			  goto out;
-		  }
+	  switch(c) {
+	  case '0'...'7':
+		*s->tck = ((c - '0') >> 2) & 1;
+		*s->tms = ((c - '0') >> 1) & 1;
+		*s->tdi = (c - '0')  & 1;
+		break;
+	  case 'r':
+	  case 's':
+		/* Deassert reset */
+		*s->ntrst = 1;
+		break;
+	  case 't':
+	  case 'u':
+		/* Assert reset */
+		*s->ntrst = 0;
+		break;
+	  case 'R':
+		val = *s->tdo + '0';
+		if(write(s->fd, &val, 1) == -1) {
+			eprintf("Error writing on socket\n");
+			ret = RC_ERROR;
+			goto out;
+		}
+		break;
+	  default:
+		break;
 	  }
+
 	  s->data_start = (s->data_start + 1) % 2048;
 	  s->datalen--;
   }
diff --git a/litex/tools/litex_sim.py b/litex/tools/litex_sim.py
index 5a1cb0da8..ac0a28c38 100755
--- a/litex/tools/litex_sim.py
+++ b/litex/tools/litex_sim.py
@@ -135,6 +135,7 @@ _io = [
         Subsignal("tms", Pins(1)),
         Subsignal("tdi", Pins(1)),
         Subsignal("tdo", Pins(1)),
+        Subsignal("ntrst", Pins(1)),
     ),
 
     # Video (VGA).
@@ -277,10 +278,7 @@ class SimSoC(SoCCore):
         # JTAG -------------------------------------------------------------------------------------
         if with_jtag:
             jtag_pads = platform.request("jtag")
-            self.comb += self.cpu.jtag_clk.eq(jtag_pads.tck)
-            self.comb += self.cpu.jtag_tms.eq(jtag_pads.tms)
-            self.comb += self.cpu.jtag_tdi.eq(jtag_pads.tdi)
-            self.comb += jtag_pads.tdo.eq(self.cpu.jtag_tdo)
+            self.cpu.add_jtag(jtag_pads)
 
         # SDCard -----------------------------------------------------------------------------------
         if with_sdcard: