Konstantin Kochin / Mbed OS STM32F103C8T6_USBSerial_Demo

Demo of the usage USBDevice library with Blue Pill STM32F103C8T6 board.

Dependencies:   USBDevice

STM32F103C8T6 USBSerial Demo

This project contains demo of the USB serial usage for a cheap developer board Blue Pill with STM32F103C8T6 mcu.

/media/uploads/vznncv/stm32f103c8_usbserial.jpg

The USB serial port provides a good communication channel between PC and microcontroller. Especially it can be useful for a debug purposes.

Notes

  • by the specifications this board has only 64KB of the flash, but actually it can have 128KB, that will be useful for a debug builds as it requires about 100KB of the flash for this demo.
  • the board can have some problems with an USB because it has wrong value of the pull-up resistor
  • for steady reading of data from a serial port, the project contains python script serial_reader.py (it requires PySerial and six python libraries), that is steady to the board reloading
  • the project depends on the fork of the USBDevice library. This fork contains some fixes and support of the BLUE_PILL_STM32F103C8 target.
  • the mbed-os now contains correct code for a clock initialization of the BLUE_PILL_STM32F103C8 target, so you don't need to adjust the board clocks separately

Diff: patches/STM32F103C8T6_128KB.ld

Revision:
0:24604e97c40c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/patches/STM32F103C8T6_128KB.ld	Fri Aug 04 18:41:22 2017 +0300
@@ -0,0 +1,155 @@
+/* Linker script for Blue Pill STM32F103C8T6 with 128KB flash memory. */
+/* Linker script to configure memory regions. */
+MEMORY
+{ 
+  FLASH (rx) : ORIGIN = 0x08000000, LENGTH = 128K
+  RAM (rwx) : ORIGIN = 0x200000EC, LENGTH = 20K - 0xEC
+}
+
+/* Linker script to place sections and symbol values. Should be used together
+ * with other linker script that defines memory regions FLASH and RAM.
+ * It references following symbols, which must be defined in code:
+ *   Reset_Handler : Entry of reset handler
+ * 
+ * It defines following symbols, which code can use without definition:
+ *   __exidx_start
+ *   __exidx_end
+ *   __etext
+ *   __data_start__
+ *   __preinit_array_start
+ *   __preinit_array_end
+ *   __init_array_start
+ *   __init_array_end
+ *   __fini_array_start
+ *   __fini_array_end
+ *   __data_end__
+ *   __bss_start__
+ *   __bss_end__
+ *   __end__
+ *   end
+ *   __HeapLimit
+ *   __StackLimit
+ *   __StackTop
+ *   __stack
+ *   _estack
+ */
+ENTRY(Reset_Handler)
+
+SECTIONS
+{
+    .text :
+    {
+        KEEP(*(.isr_vector))
+        *(.text*)
+        KEEP(*(.init))
+        KEEP(*(.fini))
+
+        /* .ctors */
+        *crtbegin.o(.ctors)
+        *crtbegin?.o(.ctors)
+        *(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors)
+        *(SORT(.ctors.*))
+        *(.ctors)
+
+        /* .dtors */
+        *crtbegin.o(.dtors)
+        *crtbegin?.o(.dtors)
+        *(EXCLUDE_FILE(*crtend?.o *crtend.o) .dtors)
+        *(SORT(.dtors.*))
+        *(.dtors)
+
+        *(.rodata*)
+
+        KEEP(*(.eh_frame*))
+    } > FLASH
+
+    .ARM.extab : 
+    {
+        *(.ARM.extab* .gnu.linkonce.armextab.*)
+    } > FLASH
+
+    __exidx_start = .;
+    .ARM.exidx :
+    {
+        *(.ARM.exidx* .gnu.linkonce.armexidx.*)
+    } > FLASH
+    __exidx_end = .;
+
+    __etext = .;
+    _sidata = .;
+
+    .data : AT (__etext)
+    {
+        __data_start__ = .;
+        _sdata = .;
+        *(vtable)
+        *(.data*)
+
+        . = ALIGN(4);
+        /* preinit data */
+        PROVIDE_HIDDEN (__preinit_array_start = .);
+        KEEP(*(.preinit_array))
+        PROVIDE_HIDDEN (__preinit_array_end = .);
+
+        . = ALIGN(4);
+        /* init data */
+        PROVIDE_HIDDEN (__init_array_start = .);
+        KEEP(*(SORT(.init_array.*)))
+        KEEP(*(.init_array))
+        PROVIDE_HIDDEN (__init_array_end = .);
+
+
+        . = ALIGN(4);
+        /* finit data */
+        PROVIDE_HIDDEN (__fini_array_start = .);
+        KEEP(*(SORT(.fini_array.*)))
+        KEEP(*(.fini_array))
+        PROVIDE_HIDDEN (__fini_array_end = .);
+
+        KEEP(*(.jcr*))
+        . = ALIGN(4);
+        /* All data end */
+        __data_end__ = .;
+        _edata = .;
+
+    } > RAM
+
+    .bss :
+    {
+        . = ALIGN(4);
+        __bss_start__ = .;
+        _sbss = .;
+        *(.bss*)
+        *(COMMON)
+        . = ALIGN(4);
+        __bss_end__ = .;
+        _ebss = .;
+    } > RAM
+    
+    .heap (COPY):
+    {
+        __end__ = .;
+        end = __end__;
+        *(.heap*)
+        __HeapLimit = .;
+    } > RAM
+
+    /* .stack_dummy section doesn't contains any symbols. It is only
+     * used for linker to calculate size of stack sections, and assign
+     * values to stack symbols later */
+    .stack_dummy (COPY):
+    {
+        *(.stack*)
+    } > RAM
+
+    /* Set stack top to end of RAM, and stack limit move down by
+     * size of stack_dummy section */
+    __StackTop = ORIGIN(RAM) + LENGTH(RAM);
+    _estack = __StackTop;
+    __StackLimit = __StackTop - SIZEOF(.stack_dummy);
+    PROVIDE(__stack = __StackTop);
+    
+    /* Check if data + heap + stack exceeds RAM limit */
+    ASSERT(__StackLimit >= __HeapLimit, "region RAM overflowed with stack")
+}
+