From 238cda0b90c3ac4ae8acc7c298391b8d449d83a2 Mon Sep 17 00:00:00 2001
From: JF <jf@codingfield.com>
Date: Fri, 19 Jun 2020 22:10:30 +0200
Subject: [PATCH] Apply fix for errata 87 (FPU issue).

---
 src/FreeRTOS/port_cmsis_systick.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/FreeRTOS/port_cmsis_systick.c b/src/FreeRTOS/port_cmsis_systick.c
index 58c51bb7..b2cc14cd 100644
--- a/src/FreeRTOS/port_cmsis_systick.c
+++ b/src/FreeRTOS/port_cmsis_systick.c
@@ -251,6 +251,14 @@ void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
             else
 #endif
             {
+                // Fix ERRATA 87 (https://infocenter.nordicsemi.com/index.jsp?topic=%252Fcom.nordic.infocenter.sdk5.v11.0.0%252Findex.html&cp=4_0_0)
+                // Clear FPU interrupt before going to sleep. This prevent unexpected wake-up.
+                #define FPU_EXCEPTION_MASK 0x0000009F
+                /* Clear exceptions and PendingIRQ from the FPU unit */
+                __set_FPSCR(__get_FPSCR()  & ~(FPU_EXCEPTION_MASK));
+                (void) __get_FPSCR();
+                NVIC_ClearPendingIRQ(FPU_IRQn);
+
                 /* No SD -  we would just block interrupts globally.
                 * BASEPRI cannot be used for that because it would prevent WFE from wake up.
                 */