From 38d7a68d9edf1e8ea6e7ed72b41705a2a5882435 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Tue, 30 Apr 2013 19:04:26 -0700
Subject: [PATCH] altos: Use separate exception stack on STM32L

This reserves 512 bytes of memory for a stack, then makes sure that
exceptions continue to use that stack while processes use the per-task
stack.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 src/core/ao_task.c      |  3 +++
 src/stm/altos.ld        |  6 ++++--
 src/stm/ao_arch_funcs.h | 14 ++++++++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/core/ao_task.c b/src/core/ao_task.c
index e1d35d67..0aad6508 100644
--- a/src/core/ao_task.c
+++ b/src/core/ao_task.c
@@ -538,5 +538,8 @@ ao_start_scheduler(void)
 	ao_cur_task_index = AO_NO_TASK_INDEX;
 #endif
 	ao_cur_task = NULL;
+#if HAS_ARCH_START_SCHEDULER
+	ao_arch_start_scheduler();
+#endif
 	ao_yield();
 }
diff --git a/src/stm/altos.ld b/src/stm/altos.ld
index 6affc376..3106cc3b 100644
--- a/src/stm/altos.ld
+++ b/src/stm/altos.ld
@@ -17,7 +17,8 @@
 
 MEMORY {
 	rom (rx) : ORIGIN = 0x08001000, LENGTH = 124K
-	ram (!w) : ORIGIN = 0x20000000, LENGTH = 16K
+	ram (!w) : ORIGIN = 0x20000000, LENGTH = 15872
+	stack (!w) : ORIGIN = 0x20003e00, LENGTH = 512
 }
 
 INCLUDE registers.ld
@@ -86,8 +87,9 @@ SECTIONS {
 		__bss_end__ = .;
 	} >ram
 
-	PROVIDE(__stack__ = ORIGIN(ram) + LENGTH(ram));
 	PROVIDE(end = .);
+
+	PROVIDE(__stack__ = ORIGIN(stack) + LENGTH(stack));
 }
 
 ENTRY(start);
diff --git a/src/stm/ao_arch_funcs.h b/src/stm/ao_arch_funcs.h
index e152440a..0d63b396 100644
--- a/src/stm/ao_arch_funcs.h
+++ b/src/stm/ao_arch_funcs.h
@@ -334,6 +334,20 @@ static inline void ao_arch_restore_stack(void) {
 	/* Return to calling function */
 	asm("bx lr");
 }
+
+#define HAS_ARCH_START_SCHEDULER	1
+
+static inline void ao_arch_start_scheduler(void) {
+	uint32_t	sp;
+	uint32_t	control;
+
+	asm("mrs %0,msp" : "=&r" (sp));
+	asm("msr psp,%0" : : "r" (sp));
+	asm("mrs %0,control" : "=&r" (control));
+	control |= (1 << 1);
+	asm("msr control,%0" : : "r" (control));
+}
+
 #endif
 
 #define ao_arch_isr_stack()
-- 
2.47.2