mimxrt: Add support for a UF2 bootloader.

Allowing to use e.g. the Adafruit bootloaders with MicroPython.  The .uf2
file is created in addition to the .bin and .hex files allowing to use the
latter ones without the bootloader for debugging and testing.

Changes:

- Set the location of the ISR Vector and .text segment to 0x6000C000 and
  0x6000C400.
- Reserve an area at the start of ITCM for a copy of the interrupt vector
  table and copy the table on reset to this place.
- Extend `machine.bootloader()` by setting the magic number to enable the
  bootloader on reset.
- Create a .uf2 file which skips the segments below 0x6000C000.

The bootloader has to be installed as a preparation step using the board
specific methods, but then the firmware's .uf2 file version can be
installed using the bootloader.  The bootloader can be invoked with:

- double reset
- calling machine.bootloader()
- Using the touch1200 method

Double reset is hard to achieve on MIMXRT boards, since there is no clean
reset pin.  Some MIMXRT boards provide it by switching the power.

Some boards are excluded from the .uf2 build:

- MIMXRT1050_EVK: The uf2 bootloader is built for the QSPI version of the
  board.  MicroPython supports the Hyperflash version.
- MIMXRT1176_EVK: No support for this board yet, but it should be possible.

Signed-off-by: robert-hh <robert@hammelrath.com>

22 files changed, 87 insertions, 20 deletions

diff --git a/ports/mimxrt/Makefile b/ports/mimxrt/Makefile
index 3a9550cc9..ad7d853b6 100644
--- a/ports/mimxrt/Makefile
+++ b/ports/mimxrt/Makefile
@@ -21,6 +21,7 @@ BUILD ?= build-$(BOARD)
 PORT ?= /dev/ttyACM0
 CROSS_COMPILE ?= arm-none-eabi-
 GIT_SUBMODULES += lib/tinyusb lib/nxp_driver
+UF2CONV ?= $(TOP)/tools/uf2conv.py
 
 # MicroPython feature configurations
 MICROPY_VFS_LFS2 ?= 1
@@ -162,6 +163,13 @@ SRC_HAL_IMX_C += \
 	$(MCU_DIR)/drivers/fsl_romapi.c
 endif
 
+# If not empty, then it is 10xx.
+ifneq ($(findstring MIMXRT10, $(MCU_SERIES)),)
+APPLICATION_ADDR := 0x6000C000
+else
+APPLICATION_ADDR := 0x3000C000
+endif
+
 ifeq ($(MCU_SERIES), MIMXRT1176)
 INC += -I$(TOP)/$(MCU_DIR)/drivers/cm7
 
@@ -253,6 +261,11 @@ else
     $(error Error: Unknown board flash type $(MICROPY_HW_FLASH_TYPE))
 endif
 
+# Set a flag if the UF2 bootloader is used
+ifeq ($(USE_UF2_BOOTLOADER),1)
+	CFLAGS += -DMICROPY_MACHINE_UF2_BOOTLOADER=1
+endif
+
 # Add sources for respective board flash type
 # Add hal/flexspi_nor_flash.c or hal/flashspi_hyper_flash.c respectively
 SRC_HAL_C += hal/flexspi_$(subst qspi_,,$(FLEXSPI_FLASH_TYPE)).c
@@ -470,7 +483,11 @@ $(BUILD)/lib/tinyusb/src/device/usbd.o: CFLAGS += -Wno-missing-braces
 # Build targets
 # =============================================================================
 
+ifeq ($(USE_UF2_BOOTLOADER),1)
+all: $(BUILD)/firmware.hex $(BUILD)/firmware.bin $(BUILD)/firmware.uf2
+else
 all: $(BUILD)/firmware.hex $(BUILD)/firmware.bin
+endif
 
 # Process linker scripts with C preprocessor to exchange LDDEFINES and
 #	aggregate output of preprocessor in a single linker script `link.ld`
@@ -487,6 +504,10 @@ $(BUILD)/firmware.bin: $(BUILD)/firmware.elf
 $(BUILD)/firmware.hex: $(BUILD)/firmware.elf
 	$(Q)$(OBJCOPY) -O ihex -R .eeprom $< $@
 
+$(BUILD)/firmware.uf2: $(BUILD)/firmware.elf
+	$(Q)$(OBJCOPY) -O binary -R .stack -R .ivt -R .flash_config $^ $@-binpart
+	$(Q)$(PYTHON) $(UF2CONV) -b $(APPLICATION_ADDR) -f MIMXRT10XX -c -o $@ $@-binpart
+
 # Making OBJ use an order-only dependency on the generated pins.h file
 # has the side effect of making the pins.h file before we actually compile
 # any of the objects. The normal dependency generation will deal with the
diff --git a/ports/mimxrt/boards/ADAFRUIT_METRO_M7/mpconfigboard.mk b/ports/mimxrt/boards/ADAFRUIT_METRO_M7/mpconfigboard.mk
index a8f7add6d..74d3a6f0f 100644
--- a/ports/mimxrt/boards/ADAFRUIT_METRO_M7/mpconfigboard.mk
+++ b/ports/mimxrt/boards/ADAFRUIT_METRO_M7/mpconfigboard.mk
@@ -8,3 +8,5 @@ MICROPY_HW_FLASH_SIZE ?= 0x800000  # 8MB
 MICROPY_PY_NETWORK_NINAW10 ?= 1
 MICROPY_PY_SSL ?= 1
 MICROPY_SSL_MBEDTLS ?= 1
+
+USE_UF2_BOOTLOADER = 1
diff --git a/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.mk b/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.mk
index dd5258590..1aef451e2 100644
--- a/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.mk
+++ b/ports/mimxrt/boards/MIMXRT1010_EVK/mpconfigboard.mk
@@ -5,6 +5,8 @@ MICROPY_FLOAT_IMPL = single
 MICROPY_HW_FLASH_TYPE = qspi_nor_flash
 MICROPY_HW_FLASH_SIZE = 0x1000000  # 16MB
 
+USE_UF2_BOOTLOADER = 1
+
 JLINK_PATH ?= /media/RT1010-EVK/
 JLINK_COMMANDER_SCRIPT = $(BUILD)/script.jlink
 
diff --git a/ports/mimxrt/boards/MIMXRT1011.ld b/ports/mimxrt/boards/MIMXRT1011.ld
index 908eefffd..ab363bd56 100644
--- a/ports/mimxrt/boards/MIMXRT1011.ld
+++ b/ports/mimxrt/boards/MIMXRT1011.ld
@@ -14,9 +14,9 @@ flash_config_start  = flash_start + 0x00000400;
 flash_config_size   = 0x00000C00;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00100000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1015.ld b/ports/mimxrt/boards/MIMXRT1015.ld
index 90336a243..0237d348c 100644
--- a/ports/mimxrt/boards/MIMXRT1015.ld
+++ b/ports/mimxrt/boards/MIMXRT1015.ld
@@ -14,9 +14,9 @@ flash_config_start  = flash_start;
 flash_config_size   = 0x00001000;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00100000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1015_EVK/mpconfigboard.mk b/ports/mimxrt/boards/MIMXRT1015_EVK/mpconfigboard.mk
index 34e5cdee5..0f719ac0a 100644
--- a/ports/mimxrt/boards/MIMXRT1015_EVK/mpconfigboard.mk
+++ b/ports/mimxrt/boards/MIMXRT1015_EVK/mpconfigboard.mk
@@ -6,3 +6,5 @@ MICROPY_HW_FLASH_TYPE = qspi_nor_flash
 MICROPY_HW_FLASH_SIZE = 0x1000000  # 16MB
 
 MICROPY_BOOT_BUFFER_SIZE = (32 * 1024)
+
+USE_UF2_BOOTLOADER = 1
diff --git a/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.mk b/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.mk
index c98843a1a..7715e669f 100644
--- a/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.mk
+++ b/ports/mimxrt/boards/MIMXRT1020_EVK/mpconfigboard.mk
@@ -12,6 +12,8 @@ MICROPY_PY_LWIP = 1
 MICROPY_PY_SSL = 1
 MICROPY_SSL_MBEDTLS = 1
 
+USE_UF2_BOOTLOADER = 1
+
 FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py
 
 JLINK_PATH ?= /media/RT1020-EVK/
diff --git a/ports/mimxrt/boards/MIMXRT1021.ld b/ports/mimxrt/boards/MIMXRT1021.ld
index bef0c13df..78add04c0 100644
--- a/ports/mimxrt/boards/MIMXRT1021.ld
+++ b/ports/mimxrt/boards/MIMXRT1021.ld
@@ -14,9 +14,9 @@ flash_config_start  = flash_start;
 flash_config_size   = 0x00001000;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00100000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1052.ld b/ports/mimxrt/boards/MIMXRT1052.ld
index ca656711a..ea034d713 100644
--- a/ports/mimxrt/boards/MIMXRT1052.ld
+++ b/ports/mimxrt/boards/MIMXRT1052.ld
@@ -16,9 +16,9 @@ flash_config_start  = flash_start;
 flash_config_size   = 0x00001000;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00200000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.mk b/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.mk
index 3af7cd231..f57aaff3b 100644
--- a/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.mk
+++ b/ports/mimxrt/boards/MIMXRT1060_EVK/mpconfigboard.mk
@@ -12,6 +12,8 @@ MICROPY_PY_LWIP = 1
 MICROPY_PY_SSL = 1
 MICROPY_SSL_MBEDTLS = 1
 
+USE_UF2_BOOTLOADER = 1
+
 FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py
 
 JLINK_PATH ?= /media/RT1060-EVK/
diff --git a/ports/mimxrt/boards/MIMXRT1062.ld b/ports/mimxrt/boards/MIMXRT1062.ld
index 5b91550d9..3d7e6d063 100644
--- a/ports/mimxrt/boards/MIMXRT1062.ld
+++ b/ports/mimxrt/boards/MIMXRT1062.ld
@@ -16,9 +16,9 @@ flash_config_start  = flash_start;
 flash_config_size   = 0x00001000;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00100000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1064.ld b/ports/mimxrt/boards/MIMXRT1064.ld
index 708dac4d5..7c35cb60c 100644
--- a/ports/mimxrt/boards/MIMXRT1064.ld
+++ b/ports/mimxrt/boards/MIMXRT1064.ld
@@ -10,9 +10,9 @@ flash_config_start  = flash_start;
 flash_config_size   = 0x00001000;
 ivt_start           = flash_start + 0x00001000;
 ivt_size            = 0x00001000;
-interrupts_start    = flash_start + 0x00002000;
+interrupts_start    = flash_start + 0x0000C000;
 interrupts_size     = 0x00000400;
-text_start          = flash_start + 0x00002400;
+text_start          = flash_start + 0x0000C400;
 vfs_start           = flash_start + 0x00100000;
 text_size           = ((vfs_start) - (text_start));
 vfs_size            = ((flash_end) - (vfs_start));
diff --git a/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.mk b/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.mk
index 95cfb4585..f175d2637 100644
--- a/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.mk
+++ b/ports/mimxrt/boards/MIMXRT1064_EVK/mpconfigboard.mk
@@ -12,6 +12,8 @@ MICROPY_PY_LWIP = 1
 MICROPY_PY_SSL = 1
 MICROPY_SSL_MBEDTLS = 1
 
+USE_UF2_BOOTLOADER = 1
+
 FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py
 
 JLINK_PATH ?= /media/RT1064-EVK/
diff --git a/ports/mimxrt/boards/OLIMEX_RT1010/mpconfigboard.mk b/ports/mimxrt/boards/OLIMEX_RT1010/mpconfigboard.mk
index 58429d298..1de497d74 100644
--- a/ports/mimxrt/boards/OLIMEX_RT1010/mpconfigboard.mk
+++ b/ports/mimxrt/boards/OLIMEX_RT1010/mpconfigboard.mk
@@ -6,6 +6,8 @@ MICROPY_HW_FLASH_TYPE = qspi_nor_flash
 MICROPY_HW_FLASH_SIZE = 0x200000  # 2MB
 MICROPY_HW_FLASH_RESERVED ?= 0x1000  # 4KB
 
+USE_UF2_BOOTLOADER = 1
+
 CFLAGS += -DMICROPY_HW_FLASH_DQS=kFlexSPIReadSampleClk_LoopbackInternally
 
 SRC_C += \
diff --git a/ports/mimxrt/boards/SEEED_ARCH_MIX/mpconfigboard.mk b/ports/mimxrt/boards/SEEED_ARCH_MIX/mpconfigboard.mk
index 63e68e1e5..c691e2dcb 100644
--- a/ports/mimxrt/boards/SEEED_ARCH_MIX/mpconfigboard.mk
+++ b/ports/mimxrt/boards/SEEED_ARCH_MIX/mpconfigboard.mk
@@ -12,6 +12,8 @@ MICROPY_PY_LWIP = 1
 MICROPY_PY_SSL = 1
 MICROPY_SSL_MBEDTLS = 1
 
+USE_UF2_BOOTLOADER = 1
+
 FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py
 
 CFLAGS += -DSPI_RETRY_TIMES=1000000
diff --git a/ports/mimxrt/boards/TEENSY40/mpconfigboard.mk b/ports/mimxrt/boards/TEENSY40/mpconfigboard.mk
index 07f174944..87c122da9 100644
--- a/ports/mimxrt/boards/TEENSY40/mpconfigboard.mk
+++ b/ports/mimxrt/boards/TEENSY40/mpconfigboard.mk
@@ -6,5 +6,7 @@ MICROPY_HW_FLASH_TYPE = qspi_nor_flash
 MICROPY_HW_FLASH_SIZE = 0x200000  # 2MB
 MICROPY_HW_FLASH_RESERVED ?= 0x1000  # 4KB
 
+USE_UF2_BOOTLOADER = 1
+
 deploy: $(BUILD)/firmware.hex
 	teensy_loader_cli --mcu=imxrt1062 -v -w $<
diff --git a/ports/mimxrt/boards/TEENSY41/mpconfigboard.mk b/ports/mimxrt/boards/TEENSY41/mpconfigboard.mk
index b297448a3..e28310d09 100755
--- a/ports/mimxrt/boards/TEENSY41/mpconfigboard.mk
+++ b/ports/mimxrt/boards/TEENSY41/mpconfigboard.mk
@@ -10,6 +10,8 @@ MICROPY_PY_LWIP = 1
 MICROPY_PY_SSL = 1
 MICROPY_SSL_MBEDTLS = 1
 
+USE_UF2_BOOTLOADER = 1
+
 FROZEN_MANIFEST ?= $(BOARD_DIR)/manifest.py
 
 deploy: $(BUILD)/firmware.hex
diff --git a/ports/mimxrt/boards/common.ld b/ports/mimxrt/boards/common.ld
index 587fc82a1..477ba38bc 100644
--- a/ports/mimxrt/boards/common.ld
+++ b/ports/mimxrt/boards/common.ld
@@ -42,7 +42,8 @@ MEMORY
   m_vfs          (RX) : ORIGIN = vfs_start,             LENGTH = vfs_size
   /* Teensy uses the last bit of flash for recovery. */
   m_reserved     (RX) : ORIGIN = (vfs_start + vfs_size), LENGTH = reserved_size
-  m_itcm         (RX) : ORIGIN = itcm_start,            LENGTH = itcm_size
+  m_isr          (RX) : ORIGIN = itcm_start,            LENGTH = 0x400
+  m_itcm         (RX) : ORIGIN = itcm_start + 0x400,    LENGTH = itcm_size - 0x400
   m_dtcm         (RW) : ORIGIN = dtcm_start,            LENGTH = dtcm_size
   m_ocrm         (RW) : ORIGIN = ocrm_start,            LENGTH = ocrm_size
 
@@ -80,7 +81,8 @@ SECTIONS
     . = ALIGN(4);
   } > m_ivt
 
-  /* The startup code goes first into internal RAM */
+  /* ISR Vector table in flash. Copied to ITCM by ResetHandler(). */
+
   .interrupts :
   {
     __Vectors = .;
@@ -90,10 +92,9 @@ SECTIONS
     . = ALIGN(4);
   } > m_interrupts
 
-  __VECTOR_RAM = __Vectors;
-  __RAM_VECTOR_TABLE_SIZE_BYTES = 0x0;
+  __Vectors_RAM = ORIGIN(m_isr);
 
-  /* The program code and other data goes into internal RAM */
+  /* Some program code and other data goes into internal RAM */
   .text :
   {
     . = ALIGN(4);
diff --git a/ports/mimxrt/hal/resethandler_MIMXRT10xx.S b/ports/mimxrt/hal/resethandler_MIMXRT10xx.S
index fe933c6d6..2fb877285 100644
--- a/ports/mimxrt/hal/resethandler_MIMXRT10xx.S
+++ b/ports/mimxrt/hal/resethandler_MIMXRT10xx.S
@@ -64,6 +64,19 @@ Reset_Handler:
  *      __ram_function_start__/__ram_function_end__ : ramfunction region
  *      copied to. Both must be aligned to 4 bytes boundary.  */
 
+/* Copy the ISR Vector table to the start of ITCM to be available when the
+   .uf2 bootloader is used */
+
+    ldr    r1, = __Vectors
+    ldr    r2, = __Vectors_RAM
+    movs   r3, 1024
+
+.LC_ISR:
+    subs    r3, #4
+    ldr    r0, [r1, r3]
+    str    r0, [r2, r3]
+    bgt    .LC_ISR
+
     ldr    r1, =__etext
     ldr    r2, =__data_start__
     ldr    r3, =__data_end__
diff --git a/ports/mimxrt/modmachine.c b/ports/mimxrt/modmachine.c
index 1212914d3..204699bcc 100644
--- a/ports/mimxrt/modmachine.c
+++ b/ports/mimxrt/modmachine.c
@@ -76,6 +76,11 @@ typedef enum {
     MP_SOFT_RESET
 } reset_reason_t;
 
+// Copied from inc/uf2.h in https://github.com/Microsoft/uf2-samd21
+#define DBL_TAP_REG   SNVS->LPGPR[3]
+#define DBL_TAP_MAGIC 0xf01669ef // Randomly selected, adjusted to have first and last bit set
+#define DBL_TAP_MAGIC_QUICK_BOOT 0xf02669ef
+
 static mp_obj_t mp_machine_unique_id(void) {
     unsigned char id[8];
     mp_hal_get_unique_id(id);
@@ -158,12 +163,17 @@ NORETURN void mp_machine_bootloader(size_t n_args, const mp_obj_t *args) {
     #if defined(MICROPY_BOARD_ENTER_BOOTLOADER)
     // If a board has a custom bootloader, call it first.
     MICROPY_BOARD_ENTER_BOOTLOADER(n_args, args);
-    #elif FSL_ROM_HAS_RUNBOOTLOADER_API
+    #elif FSL_ROM_HAS_RUNBOOTLOADER_API && !MICROPY_MACHINE_UF2_BOOTLOADER
     // If not, enter ROM bootloader in serial downloader / USB mode.
+    // Skip that in case of the UF2 bootloader being available.
     uint32_t arg = 0xEB110000;
     ROM_RunBootloader(&arg);
     #else
-    // No custom bootloader, or run bootloader API, then just reset.
+    // No custom bootloader, or run bootloader API, the set
+    // the flag for the UF2 bootloader
+    // Pretend to be the first of the two reset presses needed to enter the
+    // bootloader. That way one reset will end in the bootloader.
+    DBL_TAP_REG = DBL_TAP_MAGIC;
     WDOG_TriggerSystemSoftwareReset(WDOG1);
     #endif
     while (1) {
diff --git a/ports/mimxrt/mpconfigport.h b/ports/mimxrt/mpconfigport.h
index 923eff4dc..b45f8408e 100644
--- a/ports/mimxrt/mpconfigport.h
+++ b/ports/mimxrt/mpconfigport.h
@@ -115,6 +115,7 @@ uint32_t trng_random_u32(void);
 #define MICROPY_PY_MACHINE_UART_SENDBREAK   (1)
 #define MICROPY_PY_MACHINE_UART_IRQ         (1)
 #define MICROPY_PY_ONEWIRE                  (1)
+#define MICROPY_PY_MACHINE_BOOTLOADER       (1)
 
 // fatfs configuration used in ffconf.h
 #define MICROPY_FATFS_ENABLE_LFN            (2)
@@ -151,6 +152,7 @@ uint32_t trng_random_u32(void);
 
 #define MICROPY_HW_ENABLE_USBDEV            (1)
 #define MICROPY_HW_USB_CDC                  (1)
+#define MICROPY_HW_USB_CDC_1200BPS_TOUCH    (1)
 
 // Hooks to add builtins
 
diff --git a/tools/autobuild/build-boards.sh b/tools/autobuild/build-boards.sh
index 801e7062e..bd6828cb4 100755
--- a/tools/autobuild/build-boards.sh
+++ b/tools/autobuild/build-boards.sh
@@ -99,7 +99,7 @@ function build_esp8266_boards {
 }
 
 function build_mimxrt_boards {
-    build_boards modmimxrt.c $1 $2 bin hex
+    build_boards modmimxrt.c $1 $2 bin hex uf2
 }
 
 function build_nrf_boards {