stm32f1: Use internal functions for early USB gpio toggle

Avoid using the "low-level" library timing utilities.  This is in
preparation for using SysTick as part of the timer implementation.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/stm32f1/internal.h

@@ -8,4 +8,6 @@
 extern GPIO_TypeDef *const digital_regs[];
 extern uint32_t const digital_pins[];
 
+void udelay(uint32_t usecs);
+
 #endif // internal.h

src/stm32f1/main.c

@@ -5,6 +5,8 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include "autoconf.h"
+#include "board/internal.h" // udelay
+#include "board/misc.h" // timer_read_time
 #include "command.h" // DECL_CONSTANT
 #include "stm32f1xx.h"
 #include "stm32f1xx_ll_system.h"
@@ -19,6 +21,7 @@
 
 DECL_CONSTANT(MCU, "stm32f103");
 
+
 /****************************************************************
  * dynamic memory pool
  ****************************************************************/
@@ -128,6 +131,20 @@ void io_config(void)
     LL_DBGMCU_SetTracePinAssignment(LL_DBGMCU_TRACE_NONE);
 }
 
+// Implement simple early-boot delay mechanism
+void
+udelay(uint32_t usecs)
+{
+    if (!(CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)) {
+        CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
+        DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
+    }
+
+    uint32_t end = timer_read_time() + timer_from_us(usecs);
+    while (timer_is_before(timer_read_time(), end))
+        ;
+}
+
 // Main entry point
 int
 main(void)

src/stm32f1/usbserial.c

@@ -5,13 +5,13 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include <string.h> // NULL
+#include "board/gpio.h" // gpio_out_setup
 #include "board/io.h" // writeb
 #include "board/usb_cdc.h" // usb_notify_ep0
 #include "board/usb_cdc_ep.h" // USB_CDC_EP_BULK_IN
+#include "internal.h" // GPIO
 #include "sched.h" // DECL_INIT
 #include "stm32f1xx.h" // USB
-#include "stm32f1xx_ll_gpio.h" // LL_GPIO_SetOutputPin
-#include "stm32f1xx_ll_utils.h" // LL_mDelay
 
 
 /****************************************************************
@@ -226,10 +226,9 @@ void
 usb_init(void)
 {
     // Pull the D+ pin low briefly to signal a new connection
-    LL_GPIO_ResetOutputPin(GPIOA, LL_GPIO_PIN_12);
+    gpio_out_setup(GPIO('A', 12), 0);
-    LL_GPIO_SetPinMode(GPIOA, LL_GPIO_PIN_12, LL_GPIO_MODE_OUTPUT);
+    udelay(5000);
-    LL_mDelay(5);
+    gpio_in_setup(GPIO('A', 12), 0);
-    LL_GPIO_SetPinMode(GPIOA, LL_GPIO_PIN_12, LL_GPIO_MODE_FLOATING);
 
     // Setup USB packet memory
     btable_configure();