Fix up linker script; improve startup code; printf to USB.

10 files changed, 145 insertions, 153 deletions

diff --git a/stm/lib/usbd_cdc_core.h b/stm/lib/usbd_cdc_core.h
index 3187deb3d..026462143 100644
--- a/stm/lib/usbd_cdc_core.h
+++ b/stm/lib/usbd_cdc_core.h
@@ -97,7 +97,7 @@ typedef struct _CDC_IF_PROP
   uint16_t (*pIf_Init)     (void);   

   uint16_t (*pIf_DeInit)   (void);   

   uint16_t (*pIf_Ctrl)     (uint32_t Cmd, uint8_t* Buf, uint32_t Len);

-  uint16_t (*pIf_DataTx)   (uint8_t* Buf, uint32_t Len);

+  uint16_t (*pIf_DataTx)   (const uint8_t* Buf, uint32_t Len);

   uint16_t (*pIf_DataRx)   (uint8_t* Buf, uint32_t Len);

 }

 CDC_IF_Prop_TypeDef;

diff --git a/stm/lib/usbd_cdc_vcp.c b/stm/lib/usbd_cdc_vcp.c
index 9cf8fb258..b7330d9f6 100644
--- a/stm/lib/usbd_cdc_vcp.c
+++ b/stm/lib/usbd_cdc_vcp.c
@@ -60,7 +60,7 @@ extern uint32_t APP_Rx_ptr_in;    /* Increment this pointer or roll it back to
 static uint16_t VCP_Init     (void);

 static uint16_t VCP_DeInit   (void);

 static uint16_t VCP_Ctrl     (uint32_t Cmd, uint8_t* Buf, uint32_t Len);

-static uint16_t VCP_DataTx   (uint8_t* Buf, uint32_t Len);

+static uint16_t VCP_DataTx   (const uint8_t* Buf, uint32_t Len);

 static uint16_t VCP_DataRx   (uint8_t* Buf, uint32_t Len);

 

 CDC_IF_Prop_TypeDef VCP_fops = 

@@ -181,7 +181,7 @@ static uint16_t VCP_Ctrl (uint32_t Cmd, uint8_t* Buf, uint32_t Len)
   * @param  Len: Number of data to be sent (in bytes)

   * @retval Result of the opeartion: USBD_OK if all operations are OK else VCP_FAIL

   */

-static uint16_t VCP_DataTx (uint8_t* Buf, uint32_t Len)

+static uint16_t VCP_DataTx (const uint8_t* Buf, uint32_t Len)

 {

     for (int i = 0; i < Len; i++) {

         APP_Rx_Buffer[APP_Rx_ptr_in] = Buf[i];

@@ -212,7 +212,7 @@ static uint16_t VCP_DataTx (uint8_t* Buf, uint32_t Len)
   * @retval Result of the opeartion: USBD_OK if all operations are OK else VCP_FAIL

   */

 static uint16_t VCP_DataRx (uint8_t* Buf, uint32_t Len) {

-    printf("%.*s", (int)Len, Buf);

+    //printf("%.*s", (int)Len, Buf);

     return USBD_OK;

 }

 

diff --git a/stm/lib/usbd_conf.h b/stm/lib/usbd_conf.h
index 4bab9e3c2..60243d2f6 100644
--- a/stm/lib/usbd_conf.h
+++ b/stm/lib/usbd_conf.h
@@ -20,7 +20,4 @@
 #define MSC_MAX_PACKET              64
 #define MSC_MEDIA_PACKET            4096
 
-// for both?
-#define APP_FOPS                        VCP_fops
-
 #endif //__USBD_CONF__H__
diff --git a/stm/lib/usbd_pyb_core.c b/stm/lib/usbd_pyb_core.c
index 9c0f1caa0..ea8f05a81 100644
--- a/stm/lib/usbd_pyb_core.c
+++ b/stm/lib/usbd_pyb_core.c
@@ -96,7 +96,7 @@ static uint8_t *usbd_pyb_GetCfgDesc (uint8_t speed, uint16_t *length);
 /** @defgroup usbd_cdc_Private_Variables

   * @{

   */ 

-extern CDC_IF_Prop_TypeDef  APP_FOPS;

+extern CDC_IF_Prop_TypeDef  VCP_fops;

 extern uint8_t USBD_DeviceDesc   [USB_SIZ_DEVICE_DESC];

 

 __ALIGN_BEGIN static uint8_t usbd_cdc_AltSet __ALIGN_END = 0;

@@ -322,7 +322,7 @@ static uint8_t usbd_pyb_Init(void *pdev, uint8_t cfgidx) {
     */

 

     // Initialize the Interface physical components

-    APP_FOPS.pIf_Init();

+    VCP_fops.pIf_Init();

 

     // Prepare Out endpoint to receive next packet */

     DCD_EP_PrepareRx(pdev,

@@ -367,7 +367,7 @@ static uint8_t usbd_pyb_DeInit(void *pdev, uint8_t cfgidx) {
     DCD_EP_Close(pdev, CDC_CMD_EP);

 

     // Restore default state of the Interface physical components

-    APP_FOPS.pIf_DeInit();

+    VCP_fops.pIf_DeInit();

 

     //----------------------------------

     // MSC component

@@ -475,7 +475,7 @@ static uint8_t usbd_pyb_Setup(void *pdev, USB_SETUP_REQ *req) {
                         // Device-to-Host request

 

                         // Get the data to be sent to Host from interface layer

-                        APP_FOPS.pIf_Ctrl(req->bRequest, CmdBuff, req->wLength);

+                        VCP_fops.pIf_Ctrl(req->bRequest, CmdBuff, req->wLength);

 

                         // Send the data to the host

                         return USBD_CtlSendData(pdev, CmdBuff, req->wLength);

@@ -495,7 +495,7 @@ static uint8_t usbd_pyb_Setup(void *pdev, USB_SETUP_REQ *req) {
                     // Not a Data request

 

                     // Transfer the command to the interface layer */

-                    return APP_FOPS.pIf_Ctrl(req->bRequest, NULL, 0);

+                    return VCP_fops.pIf_Ctrl(req->bRequest, NULL, 0);

                 }

 

             } else if (req->wIndex == 2) {

@@ -537,7 +537,7 @@ static uint8_t usbd_pyb_Setup(void *pdev, USB_SETUP_REQ *req) {
 static uint8_t usbd_pyb_EP0_RxReady(void *pdev) {

     if (cdcCmd != NO_CMD) {

         // Process the data

-        APP_FOPS.pIf_Ctrl(cdcCmd, CmdBuff, cdcLen);

+        VCP_fops.pIf_Ctrl(cdcCmd, CmdBuff, cdcLen);

 

         // Reset the command variable to default value

         cdcCmd = NO_CMD;

@@ -612,7 +612,7 @@ static uint8_t usbd_pyb_DataOut(void *pdev, uint8_t epnum) {
 

             /* USB data will be immediately processed, this allow next USB traffic being 

                NAKed till the end of the application Xfer */

-            APP_FOPS.pIf_DataRx(USB_Rx_Buffer, USB_Rx_Cnt);

+            VCP_fops.pIf_DataRx(USB_Rx_Buffer, USB_Rx_Cnt);

 

             // Prepare Out endpoint to receive next packet */

             DCD_EP_PrepareRx(pdev,

diff --git a/stm/main.c b/stm/main.c
index 9eb31db53..a45a90c5e 100644
--- a/stm/main.c
+++ b/stm/main.c
@@ -6,7 +6,7 @@
 
 void delay_ms(int ms);
 
-void impl02_c_version() {
+static void impl02_c_version() {
     int x = 0;
     while (x < 400) {
         int y = 0;
@@ -52,7 +52,7 @@ void gpio_pin_af(GPIO_TypeDef *gpio, uint32_t pin, uint32_t af) {
     set_bits(&gpio->AFR[pin >> 3], 4 * (pin & 0x07), 0xf, af);
 }
 
-void mma_init() {
+static void mma_init() {
     RCC->APB1ENR |= RCC_APB1ENR_I2C1EN; // enable I2C1
     gpio_pin_init(GPIOB, 6 /* B6 is SCL */, 2 /* AF mode */, 1 /* open drain output */, 1 /* 25 MHz */, 0 /* no pull up or pull down */);
     gpio_pin_init(GPIOB, 7 /* B7 is SDA */, 2 /* AF mode */, 1 /* open drain output */, 1 /* 25 MHz */, 0 /* no pull up or pull down */);
@@ -82,14 +82,14 @@ void mma_init() {
     // set START bit in CR1 to generate a start cond!
 }
 
-uint32_t i2c_get_sr() {
+static uint32_t i2c_get_sr() {
     // must read SR1 first, then SR2, as the read can clear some flags
     uint32_t sr1 = I2C1->SR1;
     uint32_t sr2 = I2C1->SR2;
     return (sr2 << 16) | sr1;
 }
 
-void mma_restart(uint8_t addr, int write) {
+static void mma_restart(uint8_t addr, int write) {
     // send start condition
     I2C1->CR1 |= I2C_CR1_START;
 
@@ -112,7 +112,7 @@ void mma_restart(uint8_t addr, int write) {
     }
 }
 
-void mma_start(uint8_t addr, int write) {
+static void mma_start(uint8_t addr, int write) {
     // wait until I2C is not busy
     while (I2C1->SR2 & I2C_SR2_BUSY) {
     }
@@ -121,7 +121,7 @@ void mma_start(uint8_t addr, int write) {
     mma_restart(addr, write);
 }
 
-void mma_send_byte(uint8_t data) {
+static void mma_send_byte(uint8_t data) {
     // send byte
     I2C1->DR = data;
     // wait for TRA, BUSY, MSL, TXE and BTF (byte transmitted)
@@ -134,7 +134,7 @@ void mma_send_byte(uint8_t data) {
     }
 }
 
-uint8_t mma_read_ack() {
+static uint8_t mma_read_ack() {
     // enable ACK of received byte
     I2C1->CR1 |= I2C_CR1_ACK;
     // wait for BUSY, MSL and RXNE (byte received)
@@ -145,7 +145,7 @@ uint8_t mma_read_ack() {
     return data;
 }
 
-uint8_t mma_read_nack() {
+static uint8_t mma_read_nack() {
     // disable ACK of received byte (to indicate end of receiving)
     I2C1->CR1 &= (uint16_t)~((uint16_t)I2C_CR1_ACK);
     // last byte should apparently also generate a stop condition
@@ -158,7 +158,7 @@ uint8_t mma_read_nack() {
     return data;
 }
 
-void mma_stop() {
+static void mma_stop() {
     // send stop condition
     I2C1->CR1 |= I2C_CR1_STOP;
 }
@@ -440,6 +440,8 @@ py_obj_t pyb_sw() {
 FATFS fatfs0;
 
 #include "nlr.h"
+
+/*
 void g(uint i) {
     printf("g:%d\n", i);
     if (i & 1) {
@@ -467,8 +469,13 @@ void f() {
 void nlr_test() {
     f(1);
 }
+*/
+
+int dummy_bss;
 
 int main() {
+    int dummy;
+
     // should disable JTAG
 
     qstr_init();
@@ -486,12 +493,13 @@ int main() {
     for (int i = 0; i < 2; i++) {
         led_state(PYB_LEDR1_PORT_NUM, 1);
         led_state(PYB_LEDR2_PORT_NUM, 0);
-        delay_ms(200);
+        delay_ms(100);
         led_state(PYB_LEDR1_PORT_NUM, 0);
         led_state(PYB_LEDR2_PORT_NUM, 1);
-        delay_ms(200);
+        delay_ms(100);
     }
 
+    // turn LEDs off
     led_state(PYB_LEDR1_PORT_NUM, 0);
     led_state(PYB_LEDR2_PORT_NUM, 0);
     led_state(PYB_LEDG1_PORT_NUM, 0);
@@ -508,30 +516,48 @@ int main() {
     }
     */
 
-    /*
-    extern int _sidata;
-    extern int _sdata;
-    extern int _edata;
-    extern int _sbss;
-    extern int _ebss;
-    delay_ms(2000);
-    printf("_sidata=%04x\n", _sidata);
-    printf("_sdata=%04x\n", _sdata);
-    printf("_edata=%04x\n", _edata);
-    printf("_sbss=%04x\n", _sbss);
-    printf("_ebss=%04x\n", _ebss);
-    //printf("sizeof(int)=%d\n", sizeof(int)); // 4
-    delay_ms(2000);
-    */
+    // USB
+    if (1) {
+        void usb_init();
+        usb_init();
+    }
+
+    for (;;) {
+        led_state(PYB_LEDG1_PORT_NUM, 1);
+        delay_ms(100);
+        led_state(PYB_LEDG1_PORT_NUM, 0);
+        extern void *_sidata;
+        extern void *_sdata;
+        extern void *_edata;
+        extern void *_sbss;
+        extern void *_ebss;
+        extern void *_estack;
+        extern void *_etext;
+        extern void *_heap_start;
+        if (sw_get()) {
+            printf("_sidata=%p\n", &_sidata);
+            printf("_sdata=%p\n", &_sdata);
+            printf("_edata=%p\n", &_edata);
+            printf("_sbss=%p\n", &_sbss);
+            printf("_ebss=%p\n", &_ebss);
+            printf("_estack=%p\n", &_estack);
+            printf("_etext=%p\n", &_etext);
+            printf("_heap_start=%p\n", &_heap_start);
+            printf("&dummy=%p\n", &dummy);
+            printf("&dummy_bss=%p\n", &dummy_bss);
+            printf("dummy_bss=%x\n", dummy_bss);
+            //printf("sizeof(int)=%d\n", sizeof(int)); // 4
+            delay_ms(1000);
+        }
+        delay_ms(500);
+    }
 
     //printf("init;al=%u\n", m_get_total_bytes_allocated()); // 1600, due to qstr_init
     //delay_ms(1000);
 
-    nlr_test();
-
     #if 1
     // Python!
-    if (1) {
+    if (0) {
         //const char *pysrc = "def f():\n  x=x+1\nprint(42)\n";
         const char *pysrc =
             // impl01.py
@@ -802,12 +828,6 @@ int main() {
         //usb_vcp_init();
     }
 
-    // USB testing
-    if (0) {
-        void usb_init();
-        usb_init();
-    }
-
     int i = 0;
     int n = 0;
 
@@ -833,55 +853,3 @@ int main() {
 
     return 0;
 }
-
-/*
-void testf() {
-    testf(1, 2, 3);
-    testf(1, 2, 3, 4);
-    testf(1, 2, 3, 4, 5);
-    testf(1, 2, 3, 4, 5, 6);
-    testf(1, 2, 3, 4, 5, 6, 7);
-}
-
-int testg(int a, int b, int c, int d, int e) {
-    return a + b + c + d + testh(e);
-}
-
-int testh(int x, byte *y) {
-    return x + (y[-2] << 2);
-}
-*/
-
-/*
-void print_int(int x, int y, int z, int zz) {
-    printf("I %x %x %x %x", x, y, z, zz);
-    byte* ptr = (byte*)z;
-    printf("\nP %02x %02x %02x %02x", ptr[-4], ptr[-3], ptr[-2], ptr[-1]);
-    for (;;) {
-    }
-}
-void print_int_0(int x) { printf("P0 %x", x); }
-void print_int_1(int x) { printf("P1 %x", x); }
-void print_int_2(int x) { printf("P2 %x", x); }
-void print_int_3(int x) { printf("P3 %x", x); }
-void print_int_4(int x) { printf("P4 %x", x); }
-
-typedef struct _b_t {
-    void (*m1)(void*, int);
-    void (*m2)(void*, int);
-} b_t;
-typedef struct _a_t {
-    b_t *b;
-} a_t;
-void b_m1(b_t*, int);
-void b_m2(b_t*, int);
-void f1(a_t *a) {
-    a->b->m1(a->b, 2);
-    a->b->m2(a->b, 4);
-    b_m1(a->b, 2);
-    b_m2(a->b, 4);
-}
-void b_m1(b_t *b, int x) {
-    b->m1(b, x);
-}
-*/
diff --git a/stm/malloc0.c b/stm/malloc0.c
index 55c1ae804..1b45846e6 100644
--- a/stm/malloc0.c
+++ b/stm/malloc0.c
@@ -5,7 +5,8 @@ static uint32_t mem = 0;
 
 void *malloc(size_t n) {
     if (mem == 0) {
-        mem = 0x20008000; // need to use big ram block so we can execute code from it; start up a bit in case that's where bss is...?
+        extern uint32_t _heap_start;
+        mem = &_heap_start; // need to use big ram block so we can execute code from it (is it true that we can't execute from CCM?)
     }
     void *ptr = (void*)mem;
     mem = (mem + n + 3) & (~3);
diff --git a/stm/printf.c b/stm/printf.c
index 1cdb6a48f..edfee8e91 100644
--- a/stm/printf.c
+++ b/stm/printf.c
@@ -209,17 +209,17 @@ int pfenv_printf(pfenv_t *pfenv, const char *fmt, va_list args) {
 }
 
 void lcd_print_strn(const char *str, unsigned int len);
+void usb_vcp_send(const char* str, int len);
 
-void xxx(void *data, const char *str, unsigned int len) {
+void stdout_print_strn(void *data, const char *str, unsigned int len) {
+    // send stdout to LCD and USB CDC VCP
     lcd_print_strn(str, len);
+    usb_vcp_send(str, len);
 }
 
-pfenv_t pfenv_stdout = {0, xxx};
+pfenv_t pfenv_stdout = {0, stdout_print_strn};
 
 int printf(const char *fmt, ...) {
-    //pfenv_t pfenv;
-    //pfenv.data = 0;
-    //pfenv.print_strn = xxx;
     va_list args;
     va_start(args, fmt);
     return pfenv_printf(&pfenv_stdout, fmt, args);
@@ -228,15 +228,15 @@ int printf(const char *fmt, ...) {
 // need this because gcc optimises printf("%c", c) -> putchar(c), and printf("a") -> putchar('a')
 int putchar(int c) {
     char chr = c;
-    xxx(0, &chr, 1);
+    stdout_print_strn(0, &chr, 1);
     return chr;
 }
 
 // need this because gcc optimises printf("string\n") -> puts("string")
 int puts(const char *s) {
-    xxx(0, s, strlen(s));
+    stdout_print_strn(0, s, strlen(s));
     char chr = '\n';
-    xxx(0, &chr, 1);
+    stdout_print_strn(0, &chr, 1);
     return 1;
 }
 
diff --git a/stm/startup_stm32f40xx.s b/stm/startup_stm32f40xx.s
index 194ebac35..a9f21f0b0 100644
--- a/stm/startup_stm32f40xx.s
+++ b/stm/startup_stm32f40xx.s
@@ -72,6 +72,7 @@ defined in linker script */
 Reset_Handler:  
 
 /* Copy the data segment initializers from flash to SRAM */  
+/*
   movs  r1, #0
   b  LoopCopyDataInit
 
@@ -87,9 +88,23 @@ LoopCopyDataInit:
   adds  r2, r0, r1
   cmp  r2, r3
   bcc  CopyDataInit
+  */
+    ldr     r0, =_sidata        @ source pointer
+    ldr     r1, =_sdata         @ destination pointer
+    ldr     r2, =_edata         @ maximum destination pointer
+    b       data_init_entry
+data_init_loop:
+    ldr     r3, [r0], #4
+    str     r3, [r1], #4
+data_init_entry:
+    cmp     r1, r2
+    bcc     data_init_loop
+
+
+/* Zero fill the bss segment. */  
+    /*
   ldr  r2, =_sbss
   b  LoopFillZerobss
-/* Zero fill the bss segment. */  
 FillZerobss:
   movs  r3, #0
   str  r3, [r2], #4
@@ -98,6 +113,17 @@ LoopFillZerobss:
   ldr  r3, = _ebss
   cmp  r2, r3
   bcc  FillZerobss
+  */
+
+    movs    r0, #0              @ source value
+    ldr     r1, =_sbss          @ destination pointer
+    ldr     r2, =_ebss          @ maximum destination pointer
+    b       bss_init_entry
+bss_init_loop:
+    str     r0, [r1], #4
+bss_init_entry:
+    cmp     r1, r2
+    bcc     bss_init_loop
 
 /* Call the clock system intitialization function.*/
   bl  SystemInit   
diff --git a/stm/stm32f405.ld b/stm/stm32f405.ld
index bab247457..cca49bfbd 100644
--- a/stm/stm32f405.ld
+++ b/stm/stm32f405.ld
@@ -2,27 +2,22 @@
     GNU linker script for STM32F405
 */
 
-/* Entry Point */
-ENTRY(Reset_Handler)
-     
 /* Specify the memory areas */
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 0x100000 /* 1 MiB */
-    RAM_CCM (xrw)   : ORIGIN = 0x10000000, LENGTH = 0x010000 /* 64 KiB */
+    CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH = 0x010000 /* 64 KiB */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x020000 /* 128 KiB */
 }
  
-/* define stack size and heap size here */
-stack_size = 2048;
-heap_size = 0x4000; /* 16KiB */
- 
-/* define beginning and ending of stack */
-_stack_start = ORIGIN(RAM) + LENGTH(RAM);
-_stack_end = _stack_start - stack_size;
-_estack = _stack_end;
+/* produce a link error if there is not this amount of RAM for these sections */
+_minimum_stack_size = 2K;
+_minimum_heap_size = 16K;
  
-/* Define output sections */
+/* top end of the stack */
+_estack = ORIGIN(RAM) + LENGTH(RAM);
+
+/* define output sections */
 SECTIONS
 {
     /* The startup code goes first into FLASH */
@@ -30,6 +25,7 @@ SECTIONS
     {
         . = ALIGN(4);
         KEEP(*(.isr_vector)) /* Startup code */
+
         . = ALIGN(4);
     } >FLASH
    
@@ -43,10 +39,13 @@ SECTIONS
         *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
     /*  *(.glue_7)   */    /* glue arm to thumb code */
     /*  *(.glue_7t)  */    /* glue thumb to arm code */
+
         . = ALIGN(4);
-        _etext = .;        /* define a global symbols at end of code */
+        _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
      
+    /*
     .ARM.extab :
     {
         *(.ARM.extab* .gnu.linkonce.armextab.*)
@@ -58,51 +57,51 @@ SECTIONS
         *(.ARM.exidx*)
         __exidx_end = .;
     } >FLASH
+    */
         
-    /* used by the startup to initialize data */
-    _sidata = .;
-          
-    /* Initialized data sections goes into RAM, load LMA copy after code */
+    /* 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 */
+        _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 */
+        _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 */
-    . = ALIGN(4);
     .bss :
     {
-        /*  Used by the startup in order to initialize the .bss secion */
-        _sbss = .;         /* define a global symbol at bss start */
-        __bss_start__ = _sbss;
+        . = 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 */
-        __bss_end__ = _ebss;
+        _ebss = .;         /* define a global symbol at bss end; used by startup code */
     } >RAM
 
-    . = ALIGN(4);
+    /* this is to define the start of the heap, and make sure we have a minimum size */
     .heap :
     {
-        _heap_start = .;
-        . = . + heap_size;
-    } > RAM
+        . = ALIGN(4);
+        _heap_start = .;    /* define a global symbol at heap start */
+        . = . + _minimum_heap_size;
+    } >RAM
 
-    . = ALIGN(4);
-    . = _stack_end;
+    /* this just checks there is enough RAM for the stack */
     .stack :
     {
-        . = . + stack_size;
-    } > RAM
+        . = ALIGN(4);
+        . = . + _minimum_stack_size;
+        . = ALIGN(4);
+    } >RAM
 
     /* Remove information from the standard libraries */
     /*
diff --git a/stm/usb.c b/stm/usb.c
index eea7e5a0a..fdb088638 100644
--- a/stm/usb.c
+++ b/stm/usb.c
@@ -1,21 +1,22 @@
 #include "usb_core.h"
 #include "usbd_core.h"
+#include "usbd_cdc_core.h"
 #include "usbd_pyb_core.h"
 #include "usbd_usr.h"
 #include "usbd_desc.h"
 
-//extern CDC_IF_Prop_TypeDef APP_FOPS;
+extern CDC_IF_Prop_TypeDef VCP_fops;
 
+int is_enabled = 0;
 USB_OTG_CORE_HANDLE USB_OTG_dev;
 
-void usb_vcp_init() {
-    //USBD_Init(&USB_OTG_dev, USB_OTG_FS_CORE_ID, &USR_desc, &USBD_CDC_cb, &USR_cb);
+void usb_init() {
+    USBD_Init(&USB_OTG_dev, USB_OTG_FS_CORE_ID, &USR_desc, &USBD_PYB_cb, &USR_cb);
+    is_enabled = 1;
 }
 
 void usb_vcp_send(const char* str, int len) {
-    //APP_FOPS.pIf_DataTx(str, len);
-}
-
-void usb_init() {
-    USBD_Init(&USB_OTG_dev, USB_OTG_FS_CORE_ID, &USR_desc, &USBD_PYB_cb, &USR_cb);
+    if (is_enabled) {
+        VCP_fops.pIf_DataTx((const uint8_t*)str, len);
+    }
 }