From e48d343c5c67b8b3384a372b916279b5f00f8260 Mon Sep 17 00:00:00 2001
From: Christian Molson <christian@cmolabs.org>
Date: Wed, 9 Dec 2020 16:22:38 -0500
Subject: [PATCH] Fix issue with command parity, adding too many bits to
 command

---
 armsrc/em4x70.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/armsrc/em4x70.c b/armsrc/em4x70.c
index 80f04c8e9..1feb448c7 100644
--- a/armsrc/em4x70.c
+++ b/armsrc/em4x70.c
@@ -278,12 +278,18 @@ static void em4x70_send_bit(int bit) {
 
 
 /**
- * em4x70_send_command without parity
+ * em4x70_send_command
  */
 static void em4170_send_command(uint8_t command) {
     int parity = 0;
+    int msb_bit = 0;
+
+    // Non automotive EM4x70 based tags are 3 bits + 1 parity.
+    // So drop the MSB and send a parity bit instead after the command
+    if(command_parity)
+        msb_bit = 1;
     
-    for (int i = 0; i < 4; i++) {
+    for (int i = msb_bit; i < 4; i++) {
         int bit = (command >> (3 - i)) & 1;
         em4x70_send_bit(bit);
         parity ^= bit;