ports: Make new ports/ sub-directory and move all ports there.

This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.

10 files changed, 608 insertions, 0 deletions

diff --git a/ports/minimal/Makefile b/ports/minimal/Makefile
new file mode 100644
index 000000000..c95d639af
--- /dev/null
+++ b/ports/minimal/Makefile
@@ -0,0 +1,90 @@
+include ../py/mkenv.mk
+
+CROSS = 0
+
+# qstr definitions (must come before including py.mk)
+QSTR_DEFS = qstrdefsport.h
+
+# include py core make definitions
+include $(TOP)/py/py.mk
+
+ifeq ($(CROSS), 1)
+CROSS_COMPILE = arm-none-eabi-
+endif
+
+INC += -I.
+INC += -I$(TOP)
+INC += -I$(BUILD)
+
+ifeq ($(CROSS), 1)
+DFU = $(TOP)/tools/dfu.py
+PYDFU = $(TOP)/tools/pydfu.py
+CFLAGS_CORTEX_M4 = -mthumb -mtune=cortex-m4 -mabi=aapcs-linux -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard -fsingle-precision-constant -Wdouble-promotion
+CFLAGS = $(INC) -Wall -Werror -std=c99 -nostdlib $(CFLAGS_CORTEX_M4) $(COPT)
+LDFLAGS = -nostdlib -T stm32f405.ld -Map=$@.map --cref --gc-sections
+else
+LD = gcc
+CFLAGS = -m32 $(INC) -Wall -Werror -std=c99 $(COPT)
+LDFLAGS = -m32 -Wl,-Map=$@.map,--cref -Wl,--gc-sections
+endif
+
+# Tune for Debugging or Optimization
+ifeq ($(DEBUG), 1)
+CFLAGS += -O0 -ggdb
+else
+CFLAGS += -Os -DNDEBUG
+CFLAGS += -fdata-sections -ffunction-sections
+endif
+
+LIBS =
+
+SRC_C = \
+	main.c \
+	uart_core.c \
+	lib/utils/stdout_helpers.c \
+	lib/utils/pyexec.c \
+	lib/libc/string0.c \
+	lib/mp-readline/readline.c \
+	$(BUILD)/_frozen_mpy.c \
+
+OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
+
+ifeq ($(CROSS), 1)
+all: $(BUILD)/firmware.dfu
+else
+all: $(BUILD)/firmware.elf
+endif
+
+$(BUILD)/_frozen_mpy.c: frozentest.mpy $(BUILD)/genhdr/qstrdefs.generated.h
+	$(ECHO) "MISC freezing bytecode"
+	$(Q)$(TOP)/tools/mpy-tool.py -f -q $(BUILD)/genhdr/qstrdefs.preprocessed.h -mlongint-impl=none $< > $@
+
+$(BUILD)/firmware.elf: $(OBJ)
+	$(ECHO) "LINK $@"
+	$(Q)$(LD) $(LDFLAGS) -o $@ $^ $(LIBS)
+	$(Q)$(SIZE) $@
+
+$(BUILD)/firmware.bin: $(BUILD)/firmware.elf
+	$(Q)$(OBJCOPY) -O binary -j .isr_vector -j .text -j .data $^ $(BUILD)/firmware.bin
+
+$(BUILD)/firmware.dfu: $(BUILD)/firmware.bin
+	$(ECHO) "Create $@"
+	$(Q)$(PYTHON) $(DFU) -b 0x08000000:$(BUILD)/firmware.bin $@
+
+deploy: $(BUILD)/firmware.dfu
+	$(ECHO) "Writing $< to the board"
+	$(Q)$(PYTHON) $(PYDFU) -u $<
+
+# Run emulation build on a POSIX system with suitable terminal settings
+run:
+	stty raw opost -echo
+	build/firmware.elf
+	@echo Resetting terminal...
+# This sleep is useful to spot segfaults
+	sleep 1
+	reset
+
+test: $(BUILD)/firmware.elf
+	$(Q)/bin/echo -e "print('hello world!', list(x+1 for x in range(10)), end='eol\\\\n')\\r\\n\\x04" | $(BUILD)/firmware.elf | tail -n2 | grep "^hello world! \\[1, 2, 3, 4, 5, 6, 7, 8, 9, 10\\]eol"
+
+include $(TOP)/py/mkrules.mk
diff --git a/ports/minimal/README.md b/ports/minimal/README.md
new file mode 100644
index 000000000..14b8c00a3
--- /dev/null
+++ b/ports/minimal/README.md
@@ -0,0 +1,47 @@
+# The minimal port
+
+This port is intended to be a minimal MicroPython port that actually runs.
+It can run under Linux (or similar) and on any STM32F4xx MCU (eg the pyboard).
+
+## Building and running Linux version
+
+By default the port will be built for the host machine:
+
+    $ make
+
+To run a small test script do:
+
+    $ make run
+
+## Building for an STM32 MCU
+
+The Makefile has the ability to build for a Cortex-M CPU, and by default
+includes some start-up code for an STM32F4xx MCU and also enables a UART
+for communication.  To build:
+
+    $ make CROSS=1
+
+If you previously built the Linux version, you will need to first run
+`make clean` to get rid of incompatible object files.
+
+Building will produce the build/firmware.dfu file which can be programmed
+to an MCU using:
+
+    $ make CROSS=1 deploy
+
+This version of the build will work out-of-the-box on a pyboard (and
+anything similar), and will give you a MicroPython REPL on UART1 at 9600
+baud.  Pin PA13 will also be driven high, and this turns on the red LED on
+the pyboard.
+
+## Building without the built-in MicroPython compiler
+
+This minimal port can be built with the built-in MicroPython compiler
+disabled.  This will reduce the firmware by about 20k on a Thumb2 machine,
+and by about 40k on 32-bit x86.  Without the compiler the REPL will be
+disabled, but pre-compiled scripts can still be executed.
+
+To test out this feature, change the `MICROPY_ENABLE_COMPILER` config
+option to "0" in the mpconfigport.h file in this directory.  Then
+recompile and run the firmware and it will execute the frozentest.py
+file.
diff --git a/ports/minimal/frozentest.mpy b/ports/minimal/frozentest.mpy
new file mode 100644
index 000000000..87f9581bf
--- /dev/null
+++ b/ports/minimal/frozentest.mpy
diff --git a/ports/minimal/frozentest.py b/ports/minimal/frozentest.py
new file mode 100644
index 000000000..0f99b7429
--- /dev/null
+++ b/ports/minimal/frozentest.py
@@ -0,0 +1,7 @@
+print('uPy')
+print('a long string that is not interned')
+print('a string that has unicode αβγ chars')
+print(b'bytes 1234\x01')
+print(123456789)
+for i in range(4):
+    print(i)
diff --git a/ports/minimal/main.c b/ports/minimal/main.c
new file mode 100644
index 000000000..e28cfe45e
--- /dev/null
+++ b/ports/minimal/main.c
@@ -0,0 +1,257 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "py/nlr.h"
+#include "py/compile.h"
+#include "py/runtime.h"
+#include "py/repl.h"
+#include "py/gc.h"
+#include "py/mperrno.h"
+#include "lib/utils/pyexec.h"
+
+#if MICROPY_ENABLE_COMPILER
+void do_str(const char *src, mp_parse_input_kind_t input_kind) {
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_lexer_t *lex = mp_lexer_new_from_str_len(MP_QSTR__lt_stdin_gt_, src, strlen(src), 0);
+        qstr source_name = lex->source_name;
+        mp_parse_tree_t parse_tree = mp_parse(lex, input_kind);
+        mp_obj_t module_fun = mp_compile(&parse_tree, source_name, MP_EMIT_OPT_NONE, true);
+        mp_call_function_0(module_fun);
+        nlr_pop();
+    } else {
+        // uncaught exception
+        mp_obj_print_exception(&mp_plat_print, (mp_obj_t)nlr.ret_val);
+    }
+}
+#endif
+
+static char *stack_top;
+static char heap[2048];
+
+int main(int argc, char **argv) {
+    int stack_dummy;
+    stack_top = (char*)&stack_dummy;
+
+    #if MICROPY_ENABLE_GC
+    gc_init(heap, heap + sizeof(heap));
+    #endif
+    mp_init();
+    #if MICROPY_ENABLE_COMPILER
+    #if MICROPY_REPL_EVENT_DRIVEN
+    pyexec_event_repl_init();
+    for (;;) {
+        int c = mp_hal_stdin_rx_chr();
+        if (pyexec_event_repl_process_char(c)) {
+            break;
+        }
+    }
+    #else
+    pyexec_friendly_repl();
+    #endif
+    //do_str("print('hello world!', list(x+1 for x in range(10)), end='eol\\n')", MP_PARSE_SINGLE_INPUT);
+    //do_str("for i in range(10):\r\n  print(i)", MP_PARSE_FILE_INPUT);
+    #else
+    pyexec_frozen_module("frozentest.py");
+    #endif
+    mp_deinit();
+    return 0;
+}
+
+void gc_collect(void) {
+    // WARNING: This gc_collect implementation doesn't try to get root
+    // pointers from CPU registers, and thus may function incorrectly.
+    void *dummy;
+    gc_collect_start();
+    gc_collect_root(&dummy, ((mp_uint_t)stack_top - (mp_uint_t)&dummy) / sizeof(mp_uint_t));
+    gc_collect_end();
+    gc_dump_info();
+}
+
+mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
+    mp_raise_OSError(MP_ENOENT);
+}
+
+mp_import_stat_t mp_import_stat(const char *path) {
+    return MP_IMPORT_STAT_NO_EXIST;
+}
+
+mp_obj_t mp_builtin_open(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs) {
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(mp_builtin_open_obj, 1, mp_builtin_open);
+
+void nlr_jump_fail(void *val) {
+    while (1);
+}
+
+void NORETURN __fatal_error(const char *msg) {
+    while (1);
+}
+
+#ifndef NDEBUG
+void MP_WEAK __assert_func(const char *file, int line, const char *func, const char *expr) {
+    printf("Assertion '%s' failed, at file %s:%d\n", expr, file, line);
+    __fatal_error("Assertion failed");
+}
+#endif
+
+#if MICROPY_MIN_USE_CORTEX_CPU
+
+// this is a minimal IRQ and reset framework for any Cortex-M CPU
+
+extern uint32_t _estack, _sidata, _sdata, _edata, _sbss, _ebss;
+
+void Reset_Handler(void) __attribute__((naked));
+void Reset_Handler(void) {
+    // set stack pointer
+    __asm volatile ("ldr sp, =_estack");
+    // copy .data section from flash to RAM
+    for (uint32_t *src = &_sidata, *dest = &_sdata; dest < &_edata;) {
+        *dest++ = *src++;
+    }
+    // zero out .bss section
+    for (uint32_t *dest = &_sbss; dest < &_ebss;) {
+        *dest++ = 0;
+    }
+    // jump to board initialisation
+    void _start(void);
+    _start();
+}
+
+void Default_Handler(void) {
+    for (;;) {
+    }
+}
+
+const uint32_t isr_vector[] __attribute__((section(".isr_vector"))) = {
+    (uint32_t)&_estack,
+    (uint32_t)&Reset_Handler,
+    (uint32_t)&Default_Handler, // NMI_Handler
+    (uint32_t)&Default_Handler, // HardFault_Handler
+    (uint32_t)&Default_Handler, // MemManage_Handler
+    (uint32_t)&Default_Handler, // BusFault_Handler
+    (uint32_t)&Default_Handler, // UsageFault_Handler
+    0,
+    0,
+    0,
+    0,
+    (uint32_t)&Default_Handler, // SVC_Handler
+    (uint32_t)&Default_Handler, // DebugMon_Handler
+    0,
+    (uint32_t)&Default_Handler, // PendSV_Handler
+    (uint32_t)&Default_Handler, // SysTick_Handler
+};
+
+void _start(void) {
+    // when we get here: stack is initialised, bss is clear, data is copied
+
+    // SCB->CCR: enable 8-byte stack alignment for IRQ handlers, in accord with EABI
+    *((volatile uint32_t*)0xe000ed14) |= 1 << 9;
+
+    // initialise the cpu and peripherals
+    #if MICROPY_MIN_USE_STM32_MCU
+    void stm32_init(void);
+    stm32_init();
+    #endif
+
+    // now that we have a basic system up and running we can call main
+    main(0, NULL);
+
+    // we must not return
+    for (;;) {
+    }
+}
+
+#endif
+
+#if MICROPY_MIN_USE_STM32_MCU
+
+// this is minimal set-up code for an STM32 MCU
+
+typedef struct {
+    volatile uint32_t CR;
+    volatile uint32_t PLLCFGR;
+    volatile uint32_t CFGR;
+    volatile uint32_t CIR;
+    uint32_t _1[8];
+    volatile uint32_t AHB1ENR;
+    volatile uint32_t AHB2ENR;
+    volatile uint32_t AHB3ENR;
+    uint32_t _2;
+    volatile uint32_t APB1ENR;
+    volatile uint32_t APB2ENR;
+} periph_rcc_t;
+
+typedef struct {
+    volatile uint32_t MODER;
+    volatile uint32_t OTYPER;
+    volatile uint32_t OSPEEDR;
+    volatile uint32_t PUPDR;
+    volatile uint32_t IDR;
+    volatile uint32_t ODR;
+    volatile uint16_t BSRRL;
+    volatile uint16_t BSRRH;
+    volatile uint32_t LCKR;
+    volatile uint32_t AFR[2];
+} periph_gpio_t;
+
+typedef struct {
+    volatile uint32_t SR;
+    volatile uint32_t DR;
+    volatile uint32_t BRR;
+    volatile uint32_t CR1;
+} periph_uart_t;
+
+#define USART1 ((periph_uart_t*) 0x40011000)
+#define GPIOA  ((periph_gpio_t*) 0x40020000)
+#define GPIOB  ((periph_gpio_t*) 0x40020400)
+#define RCC    ((periph_rcc_t*)  0x40023800)
+
+// simple GPIO interface
+#define GPIO_MODE_IN (0)
+#define GPIO_MODE_OUT (1)
+#define GPIO_MODE_ALT (2)
+#define GPIO_PULL_NONE (0)
+#define GPIO_PULL_UP (0)
+#define GPIO_PULL_DOWN (1)
+void gpio_init(periph_gpio_t *gpio, int pin, int mode, int pull, int alt) {
+    gpio->MODER = (gpio->MODER & ~(3 << (2 * pin))) | (mode << (2 * pin));
+    // OTYPER is left as default push-pull
+    // OSPEEDR is left as default low speed
+    gpio->PUPDR = (gpio->PUPDR & ~(3 << (2 * pin))) | (pull << (2 * pin));
+    gpio->AFR[pin >> 3] = (gpio->AFR[pin >> 3] & ~(15 << (4 * (pin & 7)))) | (alt << (4 * (pin & 7)));
+}
+#define gpio_get(gpio, pin) ((gpio->IDR >> (pin)) & 1)
+#define gpio_set(gpio, pin, value) do { gpio->ODR = (gpio->ODR & ~(1 << (pin))) | (value << pin); } while (0)
+#define gpio_low(gpio, pin) do { gpio->BSRRH = (1 << (pin)); } while (0)
+#define gpio_high(gpio, pin) do { gpio->BSRRL = (1 << (pin)); } while (0)
+
+void stm32_init(void) {
+    // basic MCU config
+    RCC->CR |= (uint32_t)0x00000001; // set HSION
+    RCC->CFGR = 0x00000000; // reset all
+    RCC->CR &= (uint32_t)0xfef6ffff; // reset HSEON, CSSON, PLLON
+    RCC->PLLCFGR = 0x24003010; // reset PLLCFGR
+    RCC->CR &= (uint32_t)0xfffbffff; // reset HSEBYP
+    RCC->CIR = 0x00000000; // disable IRQs
+
+    // leave the clock as-is (internal 16MHz)
+
+    // enable GPIO clocks
+    RCC->AHB1ENR |= 0x00000003; // GPIOAEN, GPIOBEN
+
+    // turn on an LED! (on pyboard it's the red one)
+    gpio_init(GPIOA, 13, GPIO_MODE_OUT, GPIO_PULL_NONE, 0);
+    gpio_high(GPIOA, 13);
+
+    // enable UART1 at 9600 baud (TX=B6, RX=B7)
+    gpio_init(GPIOB, 6, GPIO_MODE_ALT, GPIO_PULL_NONE, 7);
+    gpio_init(GPIOB, 7, GPIO_MODE_ALT, GPIO_PULL_NONE, 7);
+    RCC->APB2ENR |= 0x00000010; // USART1EN
+    USART1->BRR = (104 << 4) | 3; // 16MHz/(16*104.1875) = 9598 baud
+    USART1->CR1 = 0x0000200c; // USART enable, tx enable, rx enable
+}
+
+#endif
diff --git a/ports/minimal/mpconfigport.h b/ports/minimal/mpconfigport.h
new file mode 100644
index 000000000..8744ca950
--- /dev/null
+++ b/ports/minimal/mpconfigport.h
@@ -0,0 +1,97 @@
+#include <stdint.h>
+
+// options to control how MicroPython is built
+
+// You can disable the built-in MicroPython compiler by setting the following
+// config option to 0.  If you do this then you won't get a REPL prompt, but you
+// will still be able to execute pre-compiled scripts, compiled with mpy-cross.
+#define MICROPY_ENABLE_COMPILER     (1)
+
+#define MICROPY_QSTR_BYTES_IN_HASH  (1)
+#define MICROPY_QSTR_EXTRA_POOL     mp_qstr_frozen_const_pool
+#define MICROPY_ALLOC_PATH_MAX      (256)
+#define MICROPY_ALLOC_PARSE_CHUNK_INIT (16)
+#define MICROPY_EMIT_X64            (0)
+#define MICROPY_EMIT_THUMB          (0)
+#define MICROPY_EMIT_INLINE_THUMB   (0)
+#define MICROPY_COMP_MODULE_CONST   (0)
+#define MICROPY_COMP_CONST          (0)
+#define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (0)
+#define MICROPY_COMP_TRIPLE_TUPLE_ASSIGN (0)
+#define MICROPY_MEM_STATS           (0)
+#define MICROPY_DEBUG_PRINTERS      (0)
+#define MICROPY_ENABLE_GC           (1)
+#define MICROPY_GC_ALLOC_THRESHOLD  (0)
+#define MICROPY_REPL_EVENT_DRIVEN   (0)
+#define MICROPY_HELPER_REPL         (1)
+#define MICROPY_HELPER_LEXER_UNIX   (0)
+#define MICROPY_ENABLE_SOURCE_LINE  (0)
+#define MICROPY_ENABLE_DOC_STRING   (0)
+#define MICROPY_ERROR_REPORTING     (MICROPY_ERROR_REPORTING_TERSE)
+#define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (0)
+#define MICROPY_PY_ASYNC_AWAIT      (0)
+#define MICROPY_PY_BUILTINS_BYTEARRAY (0)
+#define MICROPY_PY_BUILTINS_MEMORYVIEW (0)
+#define MICROPY_PY_BUILTINS_ENUMERATE (0)
+#define MICROPY_PY_BUILTINS_FILTER  (0)
+#define MICROPY_PY_BUILTINS_FROZENSET (0)
+#define MICROPY_PY_BUILTINS_REVERSED (0)
+#define MICROPY_PY_BUILTINS_SET     (0)
+#define MICROPY_PY_BUILTINS_SLICE   (0)
+#define MICROPY_PY_BUILTINS_PROPERTY (0)
+#define MICROPY_PY_BUILTINS_MIN_MAX (0)
+#define MICROPY_PY___FILE__         (0)
+#define MICROPY_PY_GC               (0)
+#define MICROPY_PY_ARRAY            (0)
+#define MICROPY_PY_ATTRTUPLE        (0)
+#define MICROPY_PY_COLLECTIONS      (0)
+#define MICROPY_PY_MATH             (0)
+#define MICROPY_PY_CMATH            (0)
+#define MICROPY_PY_IO               (0)
+#define MICROPY_PY_STRUCT           (0)
+#define MICROPY_PY_SYS              (0)
+#define MICROPY_MODULE_FROZEN_MPY   (1)
+#define MICROPY_CPYTHON_COMPAT      (0)
+#define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_NONE)
+#define MICROPY_FLOAT_IMPL          (MICROPY_FLOAT_IMPL_NONE)
+
+// type definitions for the specific machine
+
+#define MICROPY_MAKE_POINTER_CALLABLE(p) ((void*)((mp_uint_t)(p) | 1))
+
+// This port is intended to be 32-bit, but unfortunately, int32_t for
+// different targets may be defined in different ways - either as int
+// or as long. This requires different printf formatting specifiers
+// to print such value. So, we avoid int32_t and use int directly.
+#define UINT_FMT "%u"
+#define INT_FMT "%d"
+typedef int mp_int_t; // must be pointer size
+typedef unsigned mp_uint_t; // must be pointer size
+
+typedef long mp_off_t;
+
+#define MP_PLAT_PRINT_STRN(str, len) mp_hal_stdout_tx_strn_cooked(str, len)
+
+// extra built in names to add to the global namespace
+#define MICROPY_PORT_BUILTINS \
+    { MP_ROM_QSTR(MP_QSTR_open), MP_ROM_PTR(&mp_builtin_open_obj) },
+
+// We need to provide a declaration/definition of alloca()
+#include <alloca.h>
+
+#define MICROPY_HW_BOARD_NAME "minimal"
+#define MICROPY_HW_MCU_NAME "unknown-cpu"
+
+#ifdef __linux__
+#define MICROPY_MIN_USE_STDOUT (1)
+#endif
+
+#ifdef __thumb__
+#define MICROPY_MIN_USE_CORTEX_CPU (1)
+#define MICROPY_MIN_USE_STM32_MCU (1)
+#endif
+
+#define MP_STATE_PORT MP_STATE_VM
+
+#define MICROPY_PORT_ROOT_POINTERS \
+    const char *readline_hist[8];
diff --git a/ports/minimal/mphalport.h b/ports/minimal/mphalport.h
new file mode 100644
index 000000000..60d68bd2d
--- /dev/null
+++ b/ports/minimal/mphalport.h
@@ -0,0 +1,2 @@
+static inline mp_uint_t mp_hal_ticks_ms(void) { return 0; }
+static inline void mp_hal_set_interrupt_char(char c) {}
diff --git a/ports/minimal/qstrdefsport.h b/ports/minimal/qstrdefsport.h
new file mode 100644
index 000000000..3ba897069
--- /dev/null
+++ b/ports/minimal/qstrdefsport.h
@@ -0,0 +1 @@
+// qstrs specific to this port
diff --git a/ports/minimal/stm32f405.ld b/ports/minimal/stm32f405.ld
new file mode 100644
index 000000000..a202294a5
--- /dev/null
+++ b/ports/minimal/stm32f405.ld
@@ -0,0 +1,63 @@
+/*
+    GNU linker script for STM32F405
+*/
+
+/* Specify the memory areas */
+MEMORY
+{
+    FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 0x100000 /* entire flash, 1 MiB */
+    CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH = 0x010000 /* 64 KiB */
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x020000 /* 128 KiB */
+}
+
+/* top end of the stack */
+_estack = ORIGIN(RAM) + LENGTH(RAM);
+
+/* define output sections */
+SECTIONS
+{
+    /* The program code and other data goes into FLASH */
+    .text :
+    {
+        . = ALIGN(4);
+        KEEP(*(.isr_vector)) /* isr vector table */
+        *(.text)           /* .text sections (code) */
+        *(.text*)          /* .text* sections (code) */
+        *(.rodata)         /* .rodata sections (constants, strings, etc.) */
+        *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
+
+        . = ALIGN(4);
+        _etext = .;        /* define a global symbol at end of code */
+        _sidata = _etext;  /* This is used by the startup in order to initialize the .data secion */
+    } >FLASH
+
+    /* This is the initialized data section
+    The program executes knowing that the data is in the RAM
+    but the loader puts the initial values in the FLASH (inidata).
+    It is one task of the startup to copy the initial values from FLASH to RAM. */
+    .data : AT ( _sidata )
+    {
+        . = ALIGN(4);
+        _sdata = .;        /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
+        *(.data)           /* .data sections */
+        *(.data*)          /* .data* sections */
+
+        . = ALIGN(4);
+        _edata = .;        /* define a global symbol at data end; used by startup code in order to initialise the .data section in RAM */
+    } >RAM
+
+    /* Uninitialized data section */
+    .bss :
+    {
+        . = ALIGN(4);
+        _sbss = .;         /* define a global symbol at bss start; used by startup code */
+        *(.bss)
+        *(.bss*)
+        *(COMMON)
+
+        . = ALIGN(4);
+        _ebss = .;         /* define a global symbol at bss end; used by startup code */
+    } >RAM
+
+    .ARM.attributes 0 : { *(.ARM.attributes) }
+}
diff --git a/ports/minimal/uart_core.c b/ports/minimal/uart_core.c
new file mode 100644
index 000000000..d2d17b4d1
--- /dev/null
+++ b/ports/minimal/uart_core.c
@@ -0,0 +1,44 @@
+#include <unistd.h>
+#include "py/mpconfig.h"
+
+/*
+ * Core UART functions to implement for a port
+ */
+
+#if MICROPY_MIN_USE_STM32_MCU
+typedef struct {
+    volatile uint32_t SR;
+    volatile uint32_t DR;
+} periph_uart_t;
+#define USART1 ((periph_uart_t*)0x40011000)
+#endif
+
+// Receive single character
+int mp_hal_stdin_rx_chr(void) {
+    unsigned char c = 0;
+#if MICROPY_MIN_USE_STDOUT
+    int r = read(0, &c, 1);
+    (void)r;
+#elif MICROPY_MIN_USE_STM32_MCU
+    // wait for RXNE
+    while ((USART1->SR & (1 << 5)) == 0) {
+    }
+    c = USART1->DR;
+#endif
+    return c;
+}
+
+// Send string of given length
+void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
+#if MICROPY_MIN_USE_STDOUT
+    int r = write(1, str, len);
+    (void)r;
+#elif MICROPY_MIN_USE_STM32_MCU
+    while (len--) {
+        // wait for TXE
+        while ((USART1->SR & (1 << 7)) == 0) {
+        }
+        USART1->DR = *str++;
+    }
+#endif
+}