From 97af9e3332435cfd0fbed9487df2b5c08096e973 Mon Sep 17 00:00:00 2001
From: "William D. Jones" <thor0505@comcast.net>
Date: Sun, 6 Oct 2019 20:44:06 -0400
Subject: [PATCH] msp_exp430f5529lp: Make board_millis atomic.

---
 hw/bsp/msp_exp430f5529lp/msp_exp430f5529lp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/bsp/msp_exp430f5529lp/msp_exp430f5529lp.c b/hw/bsp/msp_exp430f5529lp/msp_exp430f5529lp.c
index 4eed41a4f..937c35d92 100644
--- a/hw/bsp/msp_exp430f5529lp/msp_exp430f5529lp.c
+++ b/hw/bsp/msp_exp430f5529lp/msp_exp430f5529lp.c
@@ -200,6 +200,15 @@ void __attribute__ ((interrupt(TIMER0_A0_VECTOR))) TIMER0_A0_ISR (void)
 
 uint32_t board_millis(void)
 {
-  return system_ticks;
+  uint32_t systick_mirror;
+
+  // 32-bit update is not atomic on MSP430. We can read the bottom 16-bits,
+  // an interrupt occurs, updates _all_ 32 bits, and then we return a
+  // garbage value. And I've seen it happen!
+  TA0CCTL0 &= ~CCIE;
+  systick_mirror = system_ticks;
+  TA0CCTL0 |= CCIE;
+
+  return systick_mirror;
 }
 #endif