diff --git a/SConscript.boardloader b/SConscript.boardloader
index 725db3cc6..06131e608 100644
--- a/SConscript.boardloader
+++ b/SConscript.boardloader
@@ -86,17 +86,27 @@ env.Replace(
     OBJCOPY='arm-none-eabi-objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+if env.get('TREZOR_MODEL') == 'T':
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16'
+    CPU_CCFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mtune=cortex-m4 '
+    CPU_MODEL   = 'STM32F427xx'
+else:
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m3 -mfloat-abi=soft'
+    CPU_CCFLAGS = '-mthumb -mtune=cortex-m3 -mcpu=cortex-m3 -mfloat-abi=soft '
+    CPU_MODEL   = 'STM32F405xx'
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
     '-nostdlib '
     '-std=gnu99 -Wall -Werror -Wdouble-promotion -Wpointer-arith -fno-common '
-    '-mthumb -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard '
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
-    + CCFLAGS_MOD,
+    + CPU_CCFLAGS + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/boardloader/memory.ld -Wl,--gc-sections -Wl,-Map=build/boardloader/boardloader.map -Wl,--warn-common',
     CPPPATH=[
@@ -111,11 +121,11 @@ env.Replace(
     ] + CPPPATH_MOD,
     CPPDEFINES=[
         ('TREZOR_MODEL', '$TREZOR_MODEL'),
-        'STM32F427xx',
+        CPU_MODEL,
         'USE_HAL_DRIVER',
         ('STM32_HAL_H', '"<stm32f4xx.h>"'),
     ] + CPPDEFINES_MOD,
-    ASFLAGS='-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16',
+    ASFLAGS=CPU_ASFLAGS,
     ASPPFLAGS='$CFLAGS $CCFLAGS', )
 
 #
diff --git a/SConscript.bootloader b/SConscript.bootloader
index 601a792af..5bd3199ab 100644
--- a/SConscript.bootloader
+++ b/SConscript.bootloader
@@ -107,17 +107,27 @@ env.Replace(
     OBJCOPY='arm-none-eabi-objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+if env.get('TREZOR_MODEL') == 'T':
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16'
+    CPU_CCFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mtune=cortex-m4 '
+    CPU_MODEL   = 'STM32F427xx'
+else:
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m3 -mfloat-abi=soft'
+    CPU_CCFLAGS = '-mthumb -mtune=cortex-m3 -mcpu=cortex-m3 -mfloat-abi=soft '
+    CPU_MODEL   = 'STM32F405xx'
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
     '-nostdlib '
     '-std=gnu99 -Wall -Werror -Wdouble-promotion -Wpointer-arith -fno-common '
-    '-mthumb -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard '
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
-    + CCFLAGS_MOD,
+    + CPU_CCFLAGS + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/bootloader/memory.ld -Wl,--gc-sections -Wl,-Map=build/bootloader/bootloader.map -Wl,--warn-common',
     CPPPATH=[
@@ -133,12 +143,12 @@ env.Replace(
     ] + CPPPATH_MOD,
     CPPDEFINES=[
         ('TREZOR_MODEL', '$TREZOR_MODEL'),
-        'STM32F427xx',
+        CPU_MODEL,
         'USE_HAL_DRIVER',
         ('STM32_HAL_H', '"<stm32f4xx.h>"'),
         'PB_FIELD_16BIT',
     ] + CPPDEFINES_MOD,
-    ASFLAGS='-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16',
+    ASFLAGS=CPU_ASFLAGS,
     ASPPFLAGS='$CFLAGS $CCFLAGS', )
 
 env.Replace(
diff --git a/SConscript.firmware b/SConscript.firmware
index 6afd6cbe7..0e109dbed 100644
--- a/SConscript.firmware
+++ b/SConscript.firmware
@@ -301,17 +301,27 @@ env.Replace(
     OBJCOPY='arm-none-eabi-objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+if env.get('TREZOR_MODEL') == 'T':
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16'
+    CPU_CCFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mtune=cortex-m4 '
+    CPU_MODEL   = 'STM32F427xx'
+else:
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m3 -mfloat-abi=soft'
+    CPU_CCFLAGS = '-mthumb -mtune=cortex-m3 -mcpu=cortex-m3 -mfloat-abi=soft '
+    CPU_MODEL   = 'STM32F405xx'
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
     '-nostdlib '
     '-std=gnu99 -Wall -Werror -Wdouble-promotion -Wpointer-arith -fno-common '
-    '-mthumb -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard '
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
-    + CCFLAGS_MOD,
+    + CPU_CCFLAGS + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/firmware/memory_${TREZOR_MODEL}.ld -Wl,--gc-sections -Wl,-Map=build/firmware/firmware.map -Wl,--warn-common',
     CPPPATH=[
@@ -327,11 +337,11 @@ env.Replace(
     ] + CPPPATH_MOD,
     CPPDEFINES=[
         ('TREZOR_MODEL', '$TREZOR_MODEL'),
-        'STM32F427xx',
+        CPU_MODEL,
         'USE_HAL_DRIVER',
         ('STM32_HAL_H', '"<stm32f4xx.h>"'),
     ] + CPPDEFINES_MOD,
-    ASFLAGS='-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16',
+    ASFLAGS=CPU_ASFLAGS,
     ASPPFLAGS='$CFLAGS $CCFLAGS', )
 
 env.Replace(
diff --git a/SConscript.prodtest b/SConscript.prodtest
index 86e5854c9..769499392 100644
--- a/SConscript.prodtest
+++ b/SConscript.prodtest
@@ -76,17 +76,18 @@ env.Replace(
     OBJCOPY='arm-none-eabi-objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
     '-nostdlib '
     '-std=gnu99 -Wall -Werror -Wdouble-promotion -Wpointer-arith -fno-common '
-    '-mthumb -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard '
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
-    + CCFLAGS_MOD,
+    + CPU_CCFLAGS + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/prodtest/memory.ld -Wl,--gc-sections -Wl,-Map=build/prodtest/prodtest.map -Wl,--warn-common',
     CPPPATH=[
@@ -100,10 +101,11 @@ env.Replace(
     ] + CPPPATH_MOD,
     CPPDEFINES=[
         ('TREZOR_MODEL', '$TREZOR_MODEL'),
-        'STM32F427xx',
-        ('STM32_HAL_H', '"<stm32f4xx_hal.h>"'),
+        CPU_MODEL,
+        'USE_HAL_DRIVER',
+        ('STM32_HAL_H', '"<stm32f4xx.h>"'),
     ] + CPPDEFINES_MOD,
-    ASFLAGS='-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16',
+    ASFLAGS=CPU_ASFLAGS,
     ASPPFLAGS='$CFLAGS $CCFLAGS', )
 
 env.Replace(
diff --git a/SConscript.reflash b/SConscript.reflash
index 981eaac7a..13669604a 100644
--- a/SConscript.reflash
+++ b/SConscript.reflash
@@ -76,17 +76,27 @@ env.Replace(
     OBJCOPY='arm-none-eabi-objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+if env.get('TREZOR_MODEL') == 'T':
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16'
+    CPU_CCFLAGS = '-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -mtune=cortex-m4 '
+    CPU_MODEL   = 'STM32F427xx'
+else:
+    CPU_ASFLAGS = '-mthumb -mcpu=cortex-m3 -mfloat-abi=soft'
+    CPU_CCFLAGS = '-mthumb -mtune=cortex-m3 -mcpu=cortex-m3 -mfloat-abi=soft '
+    CPU_MODEL   = 'STM32F405xx'
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
     '-nostdlib '
     '-std=gnu99 -Wall -Werror -Wdouble-promotion -Wpointer-arith -fno-common '
-    '-mthumb -mtune=cortex-m4 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard '
     '-fsingle-precision-constant -fdata-sections -ffunction-sections '
     '-ffreestanding '
     '-fstack-protector-all '
-    + CCFLAGS_MOD,
+    + CPU_CCFLAGS + CCFLAGS_MOD,
     CCFLAGS_QSTR='-DNO_QSTR -DN_X64 -DN_X86 -DN_THUMB',
     LINKFLAGS='-T embed/reflash/memory.ld -Wl,--gc-sections -Wl,-Map=build/reflash/reflash.map -Wl,--warn-common',
     CPPPATH=[
@@ -100,10 +110,11 @@ env.Replace(
     ] + CPPPATH_MOD,
     CPPDEFINES=[
         ('TREZOR_MODEL', '$TREZOR_MODEL'),
-        'STM32F427xx',
-        ('STM32_HAL_H', '"<stm32f4xx_hal.h>"'),
+        CPU_MODEL,
+        'USE_HAL_DRIVER',
+        ('STM32_HAL_H', '"<stm32f4xx.h>"'),
     ] + CPPDEFINES_MOD,
-    ASFLAGS='-mthumb -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16',
+    ASFLAGS=CPU_ASFLAGS,
     ASPPFLAGS='$CFLAGS $CCFLAGS', )
 
 env.Replace(
diff --git a/SConscript.unix b/SConscript.unix
index fe345c3ba..da19bd4f8 100644
--- a/SConscript.unix
+++ b/SConscript.unix
@@ -247,7 +247,9 @@ env.Replace(
     OBJCOPY='objcopy', )
 
 env.Replace(
-    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'),
+    TREZOR_MODEL=env.get('ENV').get('TREZOR_MODEL', 'T'), )
+
+env.Replace(
     COPT=env.get('ENV').get('OPTIMIZE', '-Os'),
     CCFLAGS='$COPT '
     '-g3 '
diff --git a/embed/trezorhal/flash.h b/embed/trezorhal/flash.h
index 31d2fda73..4bcf8592e 100644
--- a/embed/trezorhal/flash.h
+++ b/embed/trezorhal/flash.h
@@ -60,7 +60,7 @@
 #define FLASH_SECTOR_COUNT 24
 
 // note: FLASH_SR_RDERR is STM32F42xxx and STM32F43xxx specific (STM32F427) (reference RM0090 section 3.7.5)
-#ifndef FLASH_SR_RDERR
+#ifndef STM32F427xx
 #define FLASH_SR_RDERR 0
 #endif