stm32: In link script, define start of stack separately from heap end.

Previously the end of the heap was the start (lowest address) of the stack.
With the changes in this commit these addresses are now independent,
allowing a board to place the heap and stack in separate locations.

26 files changed, 92 insertions, 86 deletions

diff --git a/ports/stm32/boards/PYBD_SF2/f722_qspi.ld b/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
index 49b46bce5..e9d6fa3c3 100644
--- a/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
+++ b/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
@@ -29,16 +29,16 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K;
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = _ram_end - 16K; /* 16k stack */
+_heap_end = _sstack;
 
 ENTRY(Reset_Handler)
 
diff --git a/ports/stm32/boards/PYBD_SF6/f767.ld b/ports/stm32/boards/PYBD_SF6/f767.ld
index 7f13eb45f..2a474fba0 100644
--- a/ports/stm32/boards/PYBD_SF6/f767.ld
+++ b/ports/stm32/boards/PYBD_SF6/f767.ld
@@ -28,16 +28,16 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 24K;
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = _ram_end - 24K; /* 24k stack */
+_heap_end = _sstack;
 
 ENTRY(Reset_Handler)
 
diff --git a/ports/stm32/boards/STM32F769DISC/f769_qspi.ld b/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
index eb2cf783e..362fab330 100644
--- a/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
+++ b/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
@@ -27,14 +27,16 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 32K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20078000; /* tunable */
+_heap_end = _sstack;
 
 ENTRY(Reset_Handler)
 
diff --git a/ports/stm32/boards/stm32f091xc.ld b/ports/stm32/boards/stm32f091xc.ld
index 73b844295..5e1e9e7bd 100644
--- a/ports/stm32/boards/stm32f091xc.ld
+++ b/ports/stm32/boards/stm32f091xc.ld
@@ -14,13 +14,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 6K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20006800; /* room for a 6k stack */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f401xd.ld b/ports/stm32/boards/stm32f401xd.ld
index 7c0e79018..50cb3c571 100644
--- a/ports/stm32/boards/stm32f401xd.ld
+++ b/ports/stm32/boards/stm32f401xd.ld
@@ -14,15 +14,15 @@ MEMORY
 
 /* produce a link error if there is not this amount of RAM for these sections */
 _minimum_stack_size = 2K;
-_minimum_heap_size = 16K;
+_minimum_heap_size = 16K; /* tunable */
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K;
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20014000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f401xe.ld b/ports/stm32/boards/stm32f401xe.ld
index e76bbad1c..78e0dc1cb 100644
--- a/ports/stm32/boards/stm32f401xe.ld
+++ b/ports/stm32/boards/stm32f401xe.ld
@@ -16,13 +16,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20014000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f405.ld b/ports/stm32/boards/stm32f405.ld
index 0375491f6..13133e8c6 100644
--- a/ports/stm32/boards/stm32f405.ld
+++ b/ports/stm32/boards/stm32f405.ld
@@ -17,13 +17,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2001c000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f411.ld b/ports/stm32/boards/stm32f411.ld
index 9e3e6bc15..8ae5f6929 100644
--- a/ports/stm32/boards/stm32f411.ld
+++ b/ports/stm32/boards/stm32f411.ld
@@ -16,13 +16,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2001c000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f413xg.ld b/ports/stm32/boards/stm32f413xg.ld
index cac313bc6..c2719b834 100644
--- a/ports/stm32/boards/stm32f413xg.ld
+++ b/ports/stm32/boards/stm32f413xg.ld
@@ -19,13 +19,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = _ram_end - 16K; /* 240K, tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f413xh.ld b/ports/stm32/boards/stm32f413xh.ld
index f6dc430e3..017dbbac1 100644
--- a/ports/stm32/boards/stm32f413xh.ld
+++ b/ports/stm32/boards/stm32f413xh.ld
@@ -19,13 +19,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = _ram_end - 16K; /* 240K, tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f429.ld b/ports/stm32/boards/stm32f429.ld
index d91f625ef..35d0736ee 100644
--- a/ports/stm32/boards/stm32f429.ld
+++ b/ports/stm32/boards/stm32f429.ld
@@ -17,13 +17,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2002c000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f439.ld b/ports/stm32/boards/stm32f439.ld
index 16c606ecc..2b51c3a37 100644
--- a/ports/stm32/boards/stm32f439.ld
+++ b/ports/stm32/boards/stm32f439.ld
@@ -18,11 +18,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* top end of the stack */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2002c000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f722.ld b/ports/stm32/boards/stm32f722.ld
index f2a1d8511..8986c68d5 100644
--- a/ports/stm32/boards/stm32f722.ld
+++ b/ports/stm32/boards/stm32f722.ld
@@ -15,13 +15,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 32K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20038000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f746.ld b/ports/stm32/boards/stm32f746.ld
index b5864453d..330dd9714 100644
--- a/ports/stm32/boards/stm32f746.ld
+++ b/ports/stm32/boards/stm32f746.ld
@@ -1,5 +1,5 @@
 /*
-    GNU linker script for STM32F405
+    GNU linker script for STM32F746
 */
 
 /* Specify the memory areas */
@@ -17,13 +17,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2004c000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f767.ld b/ports/stm32/boards/stm32f767.ld
index c05fd8021..47e992c2d 100644
--- a/ports/stm32/boards/stm32f767.ld
+++ b/ports/stm32/boards/stm32f767.ld
@@ -18,13 +18,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 32K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20078000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32f769.ld b/ports/stm32/boards/stm32f769.ld
index d6da43943..41bb321a3 100644
--- a/ports/stm32/boards/stm32f769.ld
+++ b/ports/stm32/boards/stm32f769.ld
@@ -17,13 +17,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 32K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20078000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32h743.ld b/ports/stm32/boards/stm32h743.ld
index ca429edb7..0f1c2b777 100644
--- a/ports/stm32/boards/stm32h743.ld
+++ b/ports/stm32/boards/stm32h743.ld
@@ -17,13 +17,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define tho top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2407C000; /* tunable */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32l432.ld b/ports/stm32/boards/stm32l432.ld
index 70956c95b..40515e75b 100644
--- a/ports/stm32/boards/stm32l432.ld
+++ b/ports/stm32/boards/stm32l432.ld
@@ -15,13 +15,13 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define the top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 6K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2000A800; /* room for a 6k stack */
+_heap_end = _sstack;
diff --git a/ports/stm32/boards/stm32l476xe.ld b/ports/stm32/boards/stm32l476xe.ld
index 31929517d..330ec96e6 100644
--- a/ports/stm32/boards/stm32l476xe.ld
+++ b/ports/stm32/boards/stm32l476xe.ld
@@ -18,10 +18,10 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define the top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_fs_cache_start = ORIGIN(FS_CACHE);
@@ -29,7 +29,7 @@ _ram_fs_cache_end = ORIGIN(FS_CACHE) + LENGTH(FS_CACHE);
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20014000; /* tunable */
+_heap_end = _sstack;
 
 _flash_fs_start = ORIGIN(FLASH_FS);
 _flash_fs_end   = ORIGIN(FLASH_FS) + LENGTH(FLASH_FS);
diff --git a/ports/stm32/boards/stm32l476xg.ld b/ports/stm32/boards/stm32l476xg.ld
index 59c5d90b6..7983fb39a 100644
--- a/ports/stm32/boards/stm32l476xg.ld
+++ b/ports/stm32/boards/stm32l476xg.ld
@@ -18,10 +18,10 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define the top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
+_sstack = _estack - 16K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_fs_cache_start = ORIGIN(FS_CACHE);
@@ -29,7 +29,7 @@ _ram_fs_cache_end = ORIGIN(FS_CACHE) + LENGTH(FS_CACHE);
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x20014000; /* tunable */
+_heap_end = _sstack;
 
 _flash_fs_start = ORIGIN(FLASH_FS);
 _flash_fs_end   = ORIGIN(FLASH_FS) + LENGTH(FLASH_FS);
diff --git a/ports/stm32/boards/stm32l496xg.ld b/ports/stm32/boards/stm32l496xg.ld
index b42087319..e1ceb5070 100644
--- a/ports/stm32/boards/stm32l496xg.ld
+++ b/ports/stm32/boards/stm32l496xg.ld
@@ -18,10 +18,10 @@ MEMORY
 _minimum_stack_size = 2K;
 _minimum_heap_size = 16K;
 
-/* Define the top end of the stack.  The stack is full descending so begins just
-   above last byte of RAM.  Note that EABI requires the stack to be 8-byte
-   aligned for a call. */
+/* Define the stack.  The stack is full descending so begins just above last byte
+   of RAM.  Note that EABI requires the stack to be 8-byte aligned for a call. */
 _estack = ORIGIN(RAM) + LENGTH(RAM) + LENGTH(SRAM2);
+_sstack = _estack - 206K; /* tunable */
 
 /* RAM extents for the garbage collector */
 _ram_fs_cache_start = ORIGIN(FS_CACHE);
@@ -29,7 +29,7 @@ _ram_fs_cache_end = ORIGIN(FS_CACHE) + LENGTH(FS_CACHE);
 _ram_start = ORIGIN(RAM);
 _ram_end = ORIGIN(RAM) + LENGTH(RAM) + LENGTH(SRAM2);
 _heap_start = _ebss; /* heap starts just after statically allocated memory */
-_heap_end = 0x2001C000; /* tunable */
+_heap_end = _sstack;
 
 _flash_fs_start = ORIGIN(FLASH_FS);
 _flash_fs_end   = ORIGIN(FLASH_FS) + LENGTH(FLASH_FS);
diff --git a/ports/stm32/gccollect.h b/ports/stm32/gccollect.h
index 25a74a306..4992a9689 100644
--- a/ports/stm32/gccollect.h
+++ b/ports/stm32/gccollect.h
@@ -37,6 +37,7 @@ extern uint32_t _sbss;
 extern uint32_t _ebss;
 extern uint32_t _heap_start;
 extern uint32_t _heap_end;
+extern uint32_t _sstack;
 extern uint32_t _estack;
 extern uint32_t _ram_end;
 
diff --git a/ports/stm32/main.c b/ports/stm32/main.c
index 44e29921b..523034e09 100644
--- a/ports/stm32/main.c
+++ b/ports/stm32/main.c
@@ -536,7 +536,7 @@ soft_reset:
     // to recover from limit hit.  (Limit is measured in bytes.)
     // Note: stack control relies on main thread being initialised above
     mp_stack_set_top(&_estack);
-    mp_stack_set_limit((char*)&_estack - (char*)&_heap_end - 1024);
+    mp_stack_set_limit((char*)&_estack - (char*)&_sstack - 1024);
 
     // GC init
     gc_init(MICROPY_HEAP_START, MICROPY_HEAP_END);
diff --git a/ports/stm32/modmachine.c b/ports/stm32/modmachine.c
index eca8322ea..cf615ea6a 100644
--- a/ports/stm32/modmachine.c
+++ b/ports/stm32/modmachine.c
@@ -174,6 +174,7 @@ STATIC mp_obj_t machine_info(size_t n_args, const mp_obj_t *args) {
         printf("_edata=%p\n", &_edata);
         printf("_sbss=%p\n", &_sbss);
         printf("_ebss=%p\n", &_ebss);
+        printf("_sstack=%p\n", &_sstack);
         printf("_estack=%p\n", &_estack);
         printf("_ram_start=%p\n", &_ram_start);
         printf("_heap_start=%p\n", &_heap_start);
diff --git a/ports/stm32/pybthread.c b/ports/stm32/pybthread.c
index 6baf88f66..d6e9a3f51 100644
--- a/ports/stm32/pybthread.c
+++ b/ports/stm32/pybthread.c
@@ -70,8 +70,8 @@ void pyb_thread_init(pyb_thread_t *thread) {
     thread->sp = NULL; // will be set when this thread switches out
     thread->local_state = 0; // will be set by mp_thread_init
     thread->arg = NULL;
-    thread->stack = &_heap_end;
-    thread->stack_len = ((uint32_t)&_estack - (uint32_t)&_heap_end) / sizeof(uint32_t);
+    thread->stack = &_sstack;
+    thread->stack_len = ((uint32_t)&_estack - (uint32_t)&_sstack) / sizeof(uint32_t);
     thread->all_next = NULL;
     thread->run_prev = thread;
     thread->run_next = thread;
diff --git a/ports/stm32/stm32_it.c b/ports/stm32/stm32_it.c
index 078b143bb..0c5263e05 100644
--- a/ports/stm32/stm32_it.c
+++ b/ports/stm32/stm32_it.c
@@ -181,7 +181,7 @@ void HardFault_C_Handler(ExceptionRegisters_t *regs) {
     if ((void*)&_ram_start <= (void*)regs && (void*)regs < (void*)&_ram_end) {
         mp_hal_stdout_tx_str("Stack:\r\n");
         uint32_t *stack_top = &_estack;
-        if ((void*)regs < (void*)&_heap_end) {
+        if ((void*)regs < (void*)&_sstack) {
             // stack not in static stack area so limit the amount we print
             stack_top = (uint32_t*)regs + 32;
         }