stm32: Add option to put ISR, flash and UART code in RAM.

This allows UART RX to function while flash erase/writes operations are
under way, preventing lost serial data so long as it fits in the UART RX
buffer.

This enables (among other things) mpremote to successfully copy files to
boards that use a UART REPL.

Enable via the following option placed in `mpconfigboard.mk`:

    MICROPY_HW_ENABLE_ISR_UART_FLASH_FUNCS_IN_RAM = 1

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

28 files changed, 109 insertions, 48 deletions

diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index 497e409c6..806added4 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -143,7 +143,15 @@ CFLAGS += -DMICROPY_FLOAT_IMPL=MICROPY_FLOAT_IMPL_FLOAT
 CFLAGS += -fsingle-precision-constant
 endif
 
-LDFLAGS += -nostdlib -L $(LD_DIR) $(addprefix -T,$(LD_FILES)) -Wl,-Map=$(@:.elf=.map) -Wl,--cref
+# Configure linker include dir for ram/rom isr support
+ifeq ($(MICROPY_HW_ENABLE_ISR_UART_FLASH_FUNCS_IN_RAM),1)
+CFLAGS += -DMICROPY_HW_ENABLE_ISR_UART_FLASH_FUNCS_IN_RAM=1
+LD_ISR_DIR = boards/common_isr_ram
+else
+LD_ISR_DIR = boards/common_isr_rom
+endif
+
+LDFLAGS += -nostdlib -L $(LD_DIR) -L $(LD_ISR_DIR) $(addprefix -T,$(LD_FILES)) -Wl,-Map=$(@:.elf=.map) -Wl,--cref
 LDFLAGS += -Wl,--defsym=_estack_reserve=8
 LIBS += "$(shell $(CC) $(CFLAGS) -print-libgcc-file-name)"
 
@@ -465,7 +473,8 @@ OBJ += $(GEN_PINS_SRC:.c=.o)
 # Don't use -O3 with this file because gcc tries to optimise memset in terms of itself.
 $(BUILD)/shared/libc/string0.o: COPT += -O2
 
-# We put several files into the first 16K section with the ISRs.
+ifneq ($(MICROPY_HW_ENABLE_ISR_UART_FLASH_FUNCS_IN_RAM),1)
+# If MBOOT or RAM_IFS is not used we put several files into the first 16K section with the ISRs.
 # If we compile these using -O0 then it won't fit. So if you really want these
 # to be compiled with -O0, then edit boards/common.ld (in the .isr_vector section)
 # and comment out the following lines.
@@ -474,6 +483,7 @@ $(filter $(PY_BUILD)/../extmod/vfs_fat_%.o, $(PY_O)): COPT += -Os
 $(PY_BUILD)/formatfloat.o: COPT += -Os
 $(PY_BUILD)/parsenum.o: COPT += -Os
 $(PY_BUILD)/mpprint.o: COPT += -Os
+endif
 
 all: $(TOP)/lib/stm32lib/README.md all_main $(BUILD)/firmware.hex
 
@@ -557,7 +567,7 @@ TEXT0_ADDR ?= 0x08000000
 ifeq ($(TEXT1_ADDR),)
 # No TEXT1_ADDR given so put all firmware at TEXT0_ADDR location
 
-TEXT0_SECTIONS ?= .isr_vector .text .data .ARM
+TEXT0_SECTIONS ?= .isr_vector .isr_extratext .text .data .ARM
 
 deploy-stlink: $(BUILD)/firmware.bin
 	$(call RUN_STLINK,$^,$(TEXT0_ADDR))
@@ -574,7 +584,7 @@ $(BUILD)/firmware.dfu: $(BUILD)/firmware.bin
 else
 # TEXT0_ADDR and TEXT1_ADDR are specified so split firmware between these locations
 
-TEXT0_SECTIONS ?= .isr_vector
+TEXT0_SECTIONS ?= .isr_vector .isr_extratext
 TEXT1_SECTIONS ?= .text .data .ARM
 
 deploy-stlink: $(BUILD)/firmware0.bin $(BUILD)/firmware1.bin
diff --git a/ports/stm32/boards/PYBD_SF2/f722_qspi.ld b/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
index 6ce4c74c3..70d7f9cc4 100644
--- a/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
+++ b/ports/stm32/boards/PYBD_SF2/f722_qspi.ld
@@ -19,7 +19,6 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 512K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 32K     /* sectors 0,1 */
     FLASH_APP (rx)  : ORIGIN = 0x08008000, LENGTH = 480K    /* sectors 2-7 */
     FLASH_EXT (rx)  : ORIGIN = 0x90000000, LENGTH = 2048K   /* external QSPI */
     RAM (rwx)       : ORIGIN = 0x20000000, LENGTH = 256K    /* DTCM+SRAM1+SRAM2 */
diff --git a/ports/stm32/boards/PYBD_SF6/f767.ld b/ports/stm32/boards/PYBD_SF6/f767.ld
index 167d2c6a1..4262a48a9 100644
--- a/ports/stm32/boards/PYBD_SF6/f767.ld
+++ b/ports/stm32/boards/PYBD_SF6/f767.ld
@@ -17,7 +17,6 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
     FLASH_APP (rx)  : ORIGIN = 0x08008000, LENGTH = 2016K   /* sectors 1-11 3x32K 1*128K 7*256K */
     FLASH_EXT (rx)  : ORIGIN = 0x90000000, LENGTH = 2048K   /* external QSPI */
     RAM (rwx)       : ORIGIN = 0x20000000, LENGTH = 512K    /* DTCM=128k, SRAM1=368K, SRAM2=16K */
diff --git a/ports/stm32/boards/STM32F769DISC/f769_qspi.ld b/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
index b6515b066..cde1ef5ca 100644
--- a/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
+++ b/ports/stm32/boards/STM32F769DISC/f769_qspi.ld
@@ -40,6 +40,7 @@ _heap_end = _sstack;
 
 ENTRY(Reset_Handler)
 
+REGION_ALIAS("FLASH_ISR", FLASH_APP);
 REGION_ALIAS("FLASH_COMMON", FLASH_APP);
 
 SECTIONS
diff --git a/ports/stm32/boards/common_basic.ld b/ports/stm32/boards/common_basic.ld
index 9916a4c25..9c2afc3ed 100644
--- a/ports/stm32/boards/common_basic.ld
+++ b/ports/stm32/boards/common_basic.ld
@@ -12,6 +12,7 @@
 
 ENTRY(Reset_Handler)
 
+REGION_ALIAS("FLASH_ISR", FLASH);
 REGION_ALIAS("FLASH_COMMON", FLASH);
 
 /* define output sections */
diff --git a/ports/stm32/boards/common_bl.ld b/ports/stm32/boards/common_bl.ld
index b17fe9874..e2320be6f 100644
--- a/ports/stm32/boards/common_bl.ld
+++ b/ports/stm32/boards/common_bl.ld
@@ -12,6 +12,7 @@
 
 ENTRY(Reset_Handler)
 
+REGION_ALIAS("FLASH_ISR", FLASH_APP);
 REGION_ALIAS("FLASH_COMMON", FLASH_APP);
 
 /* define output sections */
diff --git a/ports/stm32/boards/common_blifs.ld b/ports/stm32/boards/common_blifs.ld
index 51969e1f9..ec6caa0a6 100644
--- a/ports/stm32/boards/common_blifs.ld
+++ b/ports/stm32/boards/common_blifs.ld
@@ -12,6 +12,7 @@
 
 ENTRY(Reset_Handler)
 
+REGION_ALIAS("FLASH_ISR", FLASH_TEXT);
 REGION_ALIAS("FLASH_COMMON", FLASH_TEXT);
 
 /* define output sections */
diff --git a/ports/stm32/boards/common_ifs.ld b/ports/stm32/boards/common_ifs.ld
index 33fa948bb..47b0190c4 100644
--- a/ports/stm32/boards/common_ifs.ld
+++ b/ports/stm32/boards/common_ifs.ld
@@ -13,36 +13,14 @@
 
 ENTRY(Reset_Handler)
 
+REGION_ALIAS("FLASH_ISR", FLASH_START);
 REGION_ALIAS("FLASH_COMMON", FLASH_TEXT);
 
 /* define output sections */
 SECTIONS
 {
-    /* The startup code goes first into FLASH */
-    .isr_vector :
-    {
-        . = ALIGN(4);
-        KEEP(*(.isr_vector)) /* Startup code */
-
-        /* This first flash block is 16K and the isr vectors only take up
-           about 400 bytes. So we pull in a couple of object files to pad it
-           out. */
-
-        . = ALIGN(4);
-
-        /* NOTE: If you update the list of files contained in .isr_vector,
-                 then be sure to also update smhal/Makefile where it forcibly
-           builds each of these files with -Os */
-
-        */ff.o(.text*)
-        */vfs_fat_*.o(.text*)
-        */py/formatfloat.o(.text*)
-        */py/parsenum.o(.text*)
-        */py/mpprint.o(.text*)
-
-        . = ALIGN(4);
-    } >FLASH_ISR
-
+    INCLUDE common_isr.ld
+    INCLUDE common_isr_extratext.ld
     INCLUDE common_text.ld
     INCLUDE common_extratext_data_in_flash.ld
     INCLUDE common_bss_heap_stack.ld
diff --git a/ports/stm32/boards/common_isr_ram/common_isr.ld b/ports/stm32/boards/common_isr_ram/common_isr.ld
new file mode 100644
index 000000000..7d8f9a64c
--- /dev/null
+++ b/ports/stm32/boards/common_isr_ram/common_isr.ld
@@ -0,0 +1,36 @@
+/* This linker script fragment is intended to be included in SECTIONS. */
+
+/* The startup code goes first into FLASH */
+.isr_vector :
+{
+    . = ALIGN(4);
+    __isr_vector_ram_start = .;
+
+    KEEP(*(.isr_vector)) /* Startup code */
+
+    /* These functions need to run from ram to enable uart
+       reception during flash erase/write operations.
+       Defining them here ensures they're copied from
+       flash (in main.c) along with the isr_vector above.
+    */
+    . = ALIGN(4);
+    *(.text.pendsv_kbd_intr)
+    *(.text.pendsv_schedule_dispatch)
+    *(.text.storage_systick_callback)
+    *(.text.SysTick_Handler)
+    *(.text.uart_irq_handler)
+    *(.text.UART*_IRQHandler)
+    *(.text.USART*_IRQHandler)
+    *(.text.FLASH_PageErase)
+    *(.text.FLASH_SectorErase)
+    *(.text.FLASH_WaitForLastOperation)
+    *(.text.HAL_FLASHEx_Erase)
+    *(.text.HAL_GetTick)
+
+    __isr_vector_ram_end = .;
+    . = ALIGN(4);
+
+} >RAM AT >FLASH_ISR
+
+/* Used by the start-up code to initialise data */
+__isr_vector_flash_addr = LOADADDR(.isr_vector);
diff --git a/ports/stm32/boards/common_isr_ram/common_isr_extratext.ld b/ports/stm32/boards/common_isr_ram/common_isr_extratext.ld
new file mode 100644
index 000000000..e69de29bb
--- /dev/null
+++ b/ports/stm32/boards/common_isr_ram/common_isr_extratext.ld
diff --git a/ports/stm32/boards/common_isr.ld b/ports/stm32/boards/common_isr_rom/common_isr.ld
index 0f9b8bcaa..8d20acde7 100644
--- a/ports/stm32/boards/common_isr.ld
+++ b/ports/stm32/boards/common_isr_rom/common_isr.ld
@@ -6,4 +6,4 @@
     . = ALIGN(4);
     KEEP(*(.isr_vector)) /* Startup code */
     . = ALIGN(4);
-} >FLASH_COMMON
+} >FLASH_ISR
diff --git a/ports/stm32/boards/common_isr_rom/common_isr_extratext.ld b/ports/stm32/boards/common_isr_rom/common_isr_extratext.ld
new file mode 100644
index 000000000..cacd32043
--- /dev/null
+++ b/ports/stm32/boards/common_isr_rom/common_isr_extratext.ld
@@ -0,0 +1,24 @@
+/* This linker script fragment is intended to be included in SECTIONS when
+   common_ifs.ld is used with common_isr.ld
+. */
+
+.isr_extratext :
+{
+    . = ALIGN(4);
+
+    /* This first flash block is 16K and the isr vectors only take up
+        about 400 bytes. So we pull in a couple of object files to pad it
+        out and save flash space in later blocks.
+
+        NOTE: If you update the list of files contained here in .isr_extratext
+        then be sure to also update stm32/Makefile where it builds each of
+        these files with -Os to keep this section as compact as possible.
+    */
+    */ff.o(.text*)
+    */vfs_fat_*.o(.text*)
+    */py/formatfloat.o(.text*)
+    */py/parsenum.o(.text*)
+    */py/mpprint.o(.text*)
+
+    . = ALIGN(4);
+} >FLASH_ISR
diff --git a/ports/stm32/boards/stm32f401xd.ld b/ports/stm32/boards/stm32f401xd.ld
index 33b2912ac..06a62d79b 100644
--- a/ports/stm32/boards/stm32f401xd.ld
+++ b/ports/stm32/boards/stm32f401xd.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 384K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 64K /* sectors 1,2,3,4: 16k+16k+16k+16k(of 64k)=64k */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 256K /* sectors 5,6 are 128K */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 80K
diff --git a/ports/stm32/boards/stm32f401xe.ld b/ports/stm32/boards/stm32f401xe.ld
index d783cd187..54994ab90 100644
--- a/ports/stm32/boards/stm32f401xe.ld
+++ b/ports/stm32/boards/stm32f401xe.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 512K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 64K /* sectors 1,2,3,4: 16k+16k+16k+16k(of 64k)=64k */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 384K /* sectors 5,6,7 are 128K */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 80K
diff --git a/ports/stm32/boards/stm32f405.ld b/ports/stm32/boards/stm32f405.ld
index 6658c1e99..792558b63 100644
--- a/ports/stm32/boards/stm32f405.ld
+++ b/ports/stm32/boards/stm32f405.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1024K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 112K /* sectors 1,2,3,4 are for filesystem */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K /* sectors 5,6,7,8,9,10,11 */
     CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH = 64K
diff --git a/ports/stm32/boards/stm32f411.ld b/ports/stm32/boards/stm32f411.ld
index 6e874f66c..ed78a7fe0 100644
--- a/ports/stm32/boards/stm32f411.ld
+++ b/ports/stm32/boards/stm32f411.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 512K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 64K /* sectors 1,2,3,4: 16k+16k+16k+16k(of 64k)=64k */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 384K /* sectors 5,6,7 are 128K */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 112K
diff --git a/ports/stm32/boards/stm32f412zx.ld b/ports/stm32/boards/stm32f412zx.ld
index c949d827a..b67f1c3e2 100644
--- a/ports/stm32/boards/stm32f412zx.ld
+++ b/ports/stm32/boards/stm32f412zx.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1024K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 64K /* sectors 1,2,3,4: 16k+16k+16k+16k(of 64k)=64k */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K /* sectors 5,6,7,8,9,10,11 are 128K */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 240K
diff --git a/ports/stm32/boards/stm32f413xg.ld b/ports/stm32/boards/stm32f413xg.ld
index cecfcaa88..95c5ecb5e 100644
--- a/ports/stm32/boards/stm32f413xg.ld
+++ b/ports/stm32/boards/stm32f413xg.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1024K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 176K /* sectors 1,2,3 are 16K, 4 is 64K, 5 is 128K (64K used) for filesystem */
     FLASH_FS2 (rx)  : ORIGIN = 0x08040000, LENGTH = 64K /* sector 6 is 128K (64K used) for filesystem, Total filesystem 240K */
     FLASH_TEXT (rx) : ORIGIN = 0x08060000, LENGTH = 640K /* sectors 7,8,9,10,11  are 128K*/
diff --git a/ports/stm32/boards/stm32f413xh.ld b/ports/stm32/boards/stm32f413xh.ld
index 0846b5c80..911f496ab 100644
--- a/ports/stm32/boards/stm32f413xh.ld
+++ b/ports/stm32/boards/stm32f413xh.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1536K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 176K /* sectors 1,2,3 are 16K, 4 is 64K, 5 is 128K (64K used) for filesystem */
     FLASH_FS2 (rx)  : ORIGIN = 0x08040000, LENGTH = 64K /* sector 6 is 128K (64K used) for filesystem, Total filesystem 240K */
     FLASH_TEXT (rx) : ORIGIN = 0x08060000, LENGTH = 1152K /* sectors 7,8,9,10,11,12,13,14,15  are 128K*/
diff --git a/ports/stm32/boards/stm32f427xi.ld b/ports/stm32/boards/stm32f427xi.ld
index b40584160..d2f6967a5 100644
--- a/ports/stm32/boards/stm32f427xi.ld
+++ b/ports/stm32/boards/stm32f427xi.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH =   16K /* sector 0, 16 KiB */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH =   16K /* sector 0, 16 KiB */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH =  112K /* sectors 1-4: 3*16K+64K */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH =  896K /* sectors 5-11 are 128K */
     CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH =   64K
diff --git a/ports/stm32/boards/stm32f429.ld b/ports/stm32/boards/stm32f429.ld
index d081c190d..38458aff9 100644
--- a/ports/stm32/boards/stm32f429.ld
+++ b/ports/stm32/boards/stm32f429.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0, 16 KiB */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0, 16 KiB */
     FLASH_FS (rx)   : ORIGIN = 0x08004000, LENGTH = 112K /* sectors 1-4: 3*16K+64K */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K /* sectors 5-11 are 128K */
     CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH = 64K
diff --git a/ports/stm32/boards/stm32f439.ld b/ports/stm32/boards/stm32f439.ld
index 64195368c..551f4ed18 100644
--- a/ports/stm32/boards/stm32f439.ld
+++ b/ports/stm32/boards/stm32f439.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K /* entire flash */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K /* sector 0 */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K /* sectors 5-11 are 128K */
     FLASH_FS (rx)   : ORIGIN = 0x08100000, LENGTH = 192K /* sectors 12-15 are 16K, 16 is 64K, 17 is 128K (64K used) */
     FLASH_FS2 (rx)  : ORIGIN = 0x08140000, LENGTH = 64K /* sector 18 is 128K (64K used) */
diff --git a/ports/stm32/boards/stm32f722.ld b/ports/stm32/boards/stm32f722.ld
index 0520f2e95..1e33295bc 100644
--- a/ports/stm32/boards/stm32f722.ld
+++ b/ports/stm32/boards/stm32f722.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 512K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 16K     /* sector 0, 16K */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 16K     /* sector 0, 16K */
     FLASH_FS (r)    : ORIGIN = 0x08004000, LENGTH = 112K    /* sectors 1-4 3*16KiB 1*64KiB*/
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 384K    /* sectors 5-7 3*128KiB = 384K */
     DTCM (xrw)      : ORIGIN = 0x20000000, LENGTH = 64K     /* Used for storage cache */
diff --git a/ports/stm32/boards/stm32f746.ld b/ports/stm32/boards/stm32f746.ld
index 854b95463..f6f33ed17 100644
--- a/ports/stm32/boards/stm32f746.ld
+++ b/ports/stm32/boards/stm32f746.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1024K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
     FLASH_FS (r)    : ORIGIN = 0x08008000, LENGTH = 96K     /* sectors 1, 2, 3 (32K each) */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K    /* sectors 4-7 1*128Kib 3*256KiB = 896K */
     DTCM (xrw)      : ORIGIN = 0x20000000, LENGTH = 64K     /* Used for storage cache */
diff --git a/ports/stm32/boards/stm32f767.ld b/ports/stm32/boards/stm32f767.ld
index 580be50dc..6c027a584 100644
--- a/ports/stm32/boards/stm32f767.ld
+++ b/ports/stm32/boards/stm32f767.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
     FLASH_APP (rx)  : ORIGIN = 0x08008000, LENGTH = 2016K   /* sectors 1-11 3x32K 1*128K 7*256K */
     FLASH_FS (r)    : ORIGIN = 0x08008000, LENGTH = 96K     /* sectors 1, 2, 3 (32K each) */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K    /* sectors 4-7 1*128Kib 3*256KiB = 896K */
diff --git a/ports/stm32/boards/stm32f769.ld b/ports/stm32/boards/stm32f769.ld
index 9fc73c859..35b1668b7 100644
--- a/ports/stm32/boards/stm32f769.ld
+++ b/ports/stm32/boards/stm32f769.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 1024K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 32K     /* sector 0, 32K */
     FLASH_FS (r)    : ORIGIN = 0x08008000, LENGTH = 96K     /* sectors 1, 2, 3 (32K each) */
     FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 896K    /* sectors 4-7 1*128Kib 3*256KiB = 896K */
     DTCM (xrw)      : ORIGIN = 0x20000000, LENGTH = 128K    /* Used for storage cache */
diff --git a/ports/stm32/boards/stm32h7b3.ld b/ports/stm32/boards/stm32h7b3.ld
index 83a261029..d9404f3d3 100644
--- a/ports/stm32/boards/stm32h7b3.ld
+++ b/ports/stm32/boards/stm32h7b3.ld
@@ -6,7 +6,7 @@
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 2048K
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 128K    /* sector 0, 128K */
+    FLASH_START (rx): ORIGIN = 0x08000000, LENGTH = 128K    /* sector 0, 128K */
     FLASH_FS (r)    : ORIGIN = 0x08020000, LENGTH = 128K    /* sector 1, 128K */
     FLASH_TEXT (rx) : ORIGIN = 0x08040000, LENGTH = 1792K   /* sectors 6*128 + 8*128 */
     DTCM (xrw)      : ORIGIN = 0x20000000, LENGTH = 128K    /* Used for storage cache */
diff --git a/ports/stm32/main.c b/ports/stm32/main.c
index 90a62c024..df483602d 100644
--- a/ports/stm32/main.c
+++ b/ports/stm32/main.c
@@ -303,10 +303,21 @@ void stm32_main(uint32_t reset_mode) {
     // Low-level MCU initialisation.
     stm32_system_init();
 
-    #if !defined(STM32F0) && defined(MICROPY_HW_VTOR)
+    #if !defined(STM32F0)
+    #if MICROPY_HW_ENABLE_ISR_UART_FLASH_FUNCS_IN_RAM
+    // Copy IRQ vector table to RAM and point VTOR there
+    extern uint32_t __isr_vector_flash_addr, __isr_vector_ram_start, __isr_vector_ram_end;
+    size_t __isr_vector_size = (&__isr_vector_ram_end - &__isr_vector_ram_start) * sizeof(uint32_t);
+    memcpy(&__isr_vector_ram_start, &__isr_vector_flash_addr, __isr_vector_size);
+    SCB->VTOR = (uint32_t)&__isr_vector_ram_start;
+    #else
+    #if defined(MICROPY_HW_VTOR)
     // Change IRQ vector table if configured differently
     SCB->VTOR = MICROPY_HW_VTOR;
     #endif
+    #endif
+    #endif
+
 
     #if __CORTEX_M != 33
     // Enable 8-byte stack alignment for IRQ handlers, in accord with EABI