diff --git a/ports/stm32/boards/PYBD_SF2/f722_qspi.ld b/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
index 49b46bce50..e9d6fa3c39 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 7f13eb45fe..2a474fba07 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 eb2cf783eb..362fab3305 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 73b8442957..5e1e9e7bd3 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 7c0e790185..50cb3c571b 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 e76bbad1c2..78e0dc1cba 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 0375491f65..13133e8c6d 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 9e3e6bc154..8ae5f6929c 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 cac313bc67..c2719b834f 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 f6dc430e32..017dbbac17 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 d91f625ef6..35d0736eef 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 16c606eccc..2b51c3a371 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 f2a1d85117..8986c68d52 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 b5864453dd..330dd97141 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 c05fd8021b..47e992c2dd 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 d6da439435..41bb321a37 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 ca429edb7b..0f1c2b777e 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 70956c95be..40515e75b3 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 31929517d7..330ec96e67 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 59c5d90b69..7983fb39a1 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 b420873199..e1ceb50707 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 25a74a306a..4992a96897 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 44e29921b1..523034e097 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 eca8322eac..cf615ea6aa 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 6baf88f66b..d6e9a3f515 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 078b143bbd..0c5263e053 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;
         }