Fix STM32L-Discovery clock setup - The X3 crystal is not fitted on the board

arch/arm/src/stm32/chip/stm32l15xxx_rcc.h

@@ -90,6 +90,12 @@
                                               /* Bits 19-23: Reserved */
 #define RCC_CR_PLLON                (1 << 24) /* Bit 24: PLL enable */
 #define RCC_CR_PLLRDY               (1 << 25) /* Bit 25: PLL clock ready flag */
+                                              /* Bits 26-27: Reserved */
+#define RCC_CR_CSSON                (1 << 28) /* Bit 16: Clock security system enable */
+#define RCC_CR_RTCPRE_SHIFT         (29)      /* Bits 29-30: RTC/LCD prescaler */
+#define RCC_CR_RTCPRE_MASK          (3 << RCC_CR_RTCPRE_SHIFT)
+                                              /* Bit 31: Reserved */
+#define RCC_CR_RSTVAL               0x00000300
 
 /* Internal clock sources calibration register */
 

arch/arm/src/stm32/stm32l15xxx_rcc.c

@@ -67,6 +67,7 @@
 
 static inline void rcc_reset(void)
 {
+#if 0 /* None of this is necessary if only called from power up */
   uint32_t regval;
 
   /* Make sure that all devices are out of reset */
@@ -82,9 +83,14 @@ static inline void rcc_reset(void)
   putreg32(0, STM32_RCC_APB1ENR);           /* Disable APB1 Peripheral Clock */
 
   /* Set the Internal clock sources calibration register to its reset value.
-   * MSI to the default frequency (nomially 2.097MHz), MSITRIM=0, HSITRIM=0x10 */
+   * MSI to the default frequency (nominally 2.097MHz), MSITRIM=0, HSITRIM=0x10.
+   * Preserve the factory HSICAL and MSICAL settings.
+   */
 
-  putreg32(RCC_ICSR_RSTVAL, STM32_RCC_ICSCR);
+  regval  = getreg32(STM32_RCC_ICSCR);
+  regval &= (RCC_ICSCR_HSICAL_MASK | RCC_ICSCR_MSICAL_MASK);
+  regval |= (RCC_ICSR_RSTVAL & ~(RCC_ICSCR_HSICAL_MASK | RCC_ICSCR_MSICAL_MASK));
+  putreg32(regval, STM32_RCC_ICSCR);
 
   /* Enable the internal MSI */
 
@@ -106,12 +112,12 @@ static inline void rcc_reset(void)
 
   while ((getreg32(STM32_RCC_CFGR) & RCC_CFGR_SWS_MASK) != RCC_CFGR_SWS_MSI);
 
-  /* Now we can disable the alternative clock sources: HSE, HSI, and PLL. Also,
+  /* Now we can disable the alternative clock sources: HSE, HSI, PLL, CSS and RTCPRE. Also,
-   * reset the HSE bypass.
+   * reset the HSE bypass.  This restores the RCC CR to its reset state.
    */
 
   regval  = getreg32(STM32_RCC_CR);         /* Disable the HSE and the PLL */
-  regval &= ~(RCC_CR_HSION | RCC_CR_HSEON | RCC_CR_PLLON);
+  regval &= ~(RCC_CR_HSION | RCC_CR_HSEON | RCC_CR_PLLON | RCC_CR_CSSON | RCC_CR_RTCPRE_MASK);
   putreg32(regval, STM32_RCC_CR);
 
   regval  = getreg32(STM32_RCC_CR);         /* Reset HSEBYP bit */
@@ -146,6 +152,7 @@ static inline void rcc_reset(void)
   putreg32(regval, STM32_FLASH_ACR);
 
   /* Check that 32-bit access is taken into account by reading FLASH_ACR */
+#endif
 }
 
 /****************************************************************************
@@ -483,19 +490,40 @@ static void stm32_stdclockconfig(void)
 {
   uint32_t regval;
 
-  /* If the PLL is using the HSE, or the HSE is the system clock */
+  /* First, enable the source clock only the PLL (via HSE or HSI), HSE, and HSI
+   * are supported in this implementation.
+   */
 
 #if (STM32_CFGR_PLLSRC == RCC_CFGR_PLLSRC) || (STM32_SYSCLK_SW == RCC_CFGR_SW_HSE)
-  /* Enable HSE clocking */
+  /* The PLL is using the HSE, or the HSE is the system clock.  In either
+   * case, we need to enable HSE clocking.
+   */
 
   if (!stm32_rcc_enablehse())
     {
       /* In the case of a timeout starting the HSE, we really don't have a
-       * strategy.  This is almost always a hardware failure or misconfiguration.
+       * strategy.  This is almost always a hardware failure or
+       * misconfiguration (for example, if no crystal is fitted on the board.
        */
 
       return;
     }
+
+#elif (STM32_CFGR_PLLSRC == 0) || (STM32_SYSCLK_SW == RCC_CFGR_SW_HSI)
+  /* The PLL is using the HSI, or the HSI is the system clock.  In either
+   * case, we need to enable HSI clocking.
+   */
+
+  regval  = getreg32(STM32_RCC_CR);   /* Enable the HSI */
+  regval |= RCC_CR_HSION;
+  putreg32(regval, STM32_RCC_CR);
+
+  /* Wait until the HSI clock is ready.  Since this is an internal clock, no
+   * timeout is expected
+   */
+
+  while ((getreg32(STM32_RCC_CR) & RCC_CR_HSIRDY) == 0);
+
 #endif
 
   /* Increasing the CPU frequency (in the same voltage range):

configs/stm32ldiscovery/README.txt

@@ -444,6 +444,11 @@ GND and (external) 5V are available on both P1 and P2.  Note:  These signals
 may be at lower voltage levels and, hence, may not properly drive an external
 RS-232 transceiver.
 
+NOTE:  The crystal X3 is not installed on the STM32L3-Discovery.  As a
+result, the HSE clock is not availabled and the less acurate HSI must be
+used.  This may limit the accuracy of the computed baud, especially at
+higher BAUD.
+
 A USB serial console is another option.
 
 Debugging
@@ -707,6 +712,8 @@ Where <subdir> is one of the following:
        USB converter.  The UART1 TX and RX pins should be available on
        PA9 and PA10, respectively.
 
+       The serial console is configured for 57600 8N1
+
     3. Support for NSH built-in applications is *not* enabled.
 
     4. By default, this configuration uses the CodeSourcery toolchain

configs/stm32ldiscovery/include/board.h

@@ -60,7 +60,8 @@
  * - HSI high-speed internal oscillator clock
  *   Generated from an internal 16 MHz RC oscillator
  * - HSE high-speed external oscillator clock
- *   Driven by the 8MHz crystal (X1) on the OSC_IN and OSC_OUT pins
+ *   Normally driven by an external crystal (X3).  However, this crystal is not fitted
+ *   on the STM32L-Discovery board.
  * - PLL clock
  * - MSI multispeed internal oscillator clock
  *   The MSI clock signal is generated from an internal RC oscillator. Seven frequency
@@ -74,7 +75,7 @@
  *   Driven by 32.768KHz crystal (X2) on the OSC32_IN and OSC32_OUT pins.
  */
 
-#define STM32_BOARD_XTAL        8000000ul        /* X1 on board */
+#define STM32_BOARD_XTAL        8000000ul        /* X3 on board (not fitted)*/
 
 #define STM32_HSI_FREQUENCY     16000000ul       /* Approximately 16MHz */
 #define STM32_HSE_FREQUENCY     STM32_BOARD_XTAL
@@ -84,11 +85,11 @@
 
 /* PLL Configuration
  *
- *   - PLL source is HSE/1    -> 8MHz input
+ *   - PLL source is HSI      -> 16MHz input (nominal)
- *   - PLL multipler is 8     -> 64MHz PLL VCO clock output
+ *   - PLL multipler is 4     -> 64MHz PLL VCO clock output
  *   - PLL output divider 2   -> 32MHz divided down PLL VCO clock output
  *
- * Resulting SYSCLK frequency is 8MHz (XTAL) x 8 / 2 = 32MHz
+ * Resulting SYSCLK frequency is 16MHz x 4 / 2 = 32MHz
  *
  * USB/SDIO:
  *   If the USB or SDIO interface is used in the application, the PLL VCO
@@ -105,10 +106,10 @@
  *   The minimum input clock frequency for PLL is 2 MHz (when using HSE as PLL source).
  */
 
-#define STM32_CFGR_PLLSRC       RCC_CFGR_PLLSRC         /* Source is 8MHz HSE */
+#define STM32_CFGR_PLLSRC       0                       /* Source is 16MHz HSI */
-#define STM32_CFGR_PLLMUL       RCC_CFGR_PLLMUL_CLKx8   /* PLLMUL = 8 */
+#define STM32_CFGR_PLLMUL       RCC_CFGR_PLLMUL_CLKx4   /* PLLMUL = 4 */
 #define STM32_CFGR_PLLDIV       RCC_CFGR_PLLDIV_2       /* PLLDIV = 2 */
-#define STM32_PLL_FREQUENCY     (8*STM32_BOARD_XTAL)    /* PLL VCO Frequency is 64MHz */
+#define STM32_PLL_FREQUENCY     (4*STM32_HSE_FREQUENCY) /* PLL VCO Frequency is 64MHz */
 
 /* Use the PLL and set the SYSCLK source to be the diveded down PLL VCO output
  * frequency (STM32_PLL_FREQUENCY divided by the PLLDIV value).
@@ -292,7 +293,7 @@ extern "C" {
  *
  ************************************************************************************/
 
-EXTERN void stm32_boardinitialize(void);
+void stm32_boardinitialize(void);
 
 /************************************************************************************
  * Name:  stm32_ledinit, stm32_setled, and stm32_setleds
@@ -305,9 +306,9 @@ EXTERN void stm32_boardinitialize(void);
  ************************************************************************************/
 
 #ifndef CONFIG_ARCH_LEDS
-EXTERN void stm32_ledinit(void);
+void stm32_ledinit(void);
-EXTERN void stm32_setled(int led, bool ledon);
+void stm32_setled(int led, bool ledon);
-EXTERN void stm32_setleds(uint8_t ledset);
+void stm32_setleds(uint8_t ledset);
 #endif
 
 /************************************************************************************
@@ -334,10 +335,10 @@ EXTERN void stm32_setleds(uint8_t ledset);
  ************************************************************************************/
 
 #ifdef CONFIG_ARCH_BUTTONS
-EXTERN void up_buttoninit(void);
+void up_buttoninit(void);
-EXTERN uint8_t up_buttons(void);
+uint8_t up_buttons(void);
 #ifdef CONFIG_ARCH_IRQBUTTONS
-EXTERN xcpt_t up_irqbutton(int id, xcpt_t irqhandler);
+xcpt_t up_irqbutton(int id, xcpt_t irqhandler);
 #endif
 #endif
 

configs/stm32ldiscovery/nsh/defconfig

@@ -406,7 +406,7 @@ CONFIG_USART1_SERIAL_CONSOLE=y
 #
 CONFIG_USART1_RXBUFSIZE=64
 CONFIG_USART1_TXBUFSIZE=64
-CONFIG_USART1_BAUD=115200
+CONFIG_USART1_BAUD=57600
 CONFIG_USART1_BITS=8
 CONFIG_USART1_PARITY=0
 CONFIG_USART1_2STOP=0

configs/stm32ldiscovery/src/stm32_userleds.c

@@ -112,7 +112,7 @@ void stm32_setled(int led, bool ledon)
     {
       ledcfg = GPIO_LED1;
     }
-  else if (led == BOARD_LED1)
+  else if (led == BOARD_LED2)
     {
       ledcfg = GPIO_LED2;
     }

configs/stm32ldiscovery/src/stm32ldiscovery.h

@@ -63,20 +63,19 @@
 #endif
 
 /* STM32L-Discovery GPIOs ***************************************************************************/
-/* The STM32L-Discovery board has four LEDs.  Two of these are controlled by
+/* The STM32L-Discovery board has four LEDs.  Two of these are controlled by logic on the board and
- * logic on the board and are not available for software control:
+ * are not available for software control:
  *
- * LD1 COM:   LD2 default status is red. LD2 turns to green to indicate that
+ * LD1 COM:   LD2 default status is red. LD2 turns to green to indicate that communications are in
- *            communications are in progress between the PC and the ST-LINK/V2.
+ *            progress between the PC and the ST-LINK/V2.
  * LD2 PWR:   Red LED indicates that the board is powered.
  *
  * And two LEDs can be controlled by software:
  *
- * User LD3:  Green LED is a user LED connected to the I/O PB7 of the STM32L152
+ * User LD3:  Green LED is a user LED connected to the I/O PB7 of the STM32L152 MCU.
- *            MCU.
+ * User LD4:  Blue LED is a user LED connected to the I/O PB6 of the STM32L152 MCU.
- * User LD4:  Blue LED is a user LED connected to the I/O PB6 of the STM32L152
- *            MCU.
  *
+ * The other side of the LED connects to ground so high value will illuminate the LED.
  */
 
 #define GPIO_LED1       (GPIO_OUTPUT | GPIO_PUSHPULL | GPIO_SPEED_10MHz | \
@@ -85,8 +84,7 @@
                          GPIO_OUTPUT_CLEAR | GPIO_PORTB | GPIO_PIN6)
 
 /* Button definitions *******************************************************************************/
-/* The STM32L-Discovery supports two buttons; only one button is controllable by
+/* The STM32L-Discovery supports two buttons; only one button is controllable by software:
- * software:
  *
  *   B1 USER: user and wake-up button connected to the I/O PA0 of the STM32F303VCT6.
  *   B2 RESET: pushbutton connected to NRST is used to RESET the STM32F303VCT6.