chore: rewrite to modbus rtu

systick.h

@@ -0,0 +1,27 @@
+#ifndef SYSTICK_H
+#define SYSTICK_H
+
+#include <stdio.h>
+
+#include "ch32v003fun.h"
+
+// Number of ticks elapsed per millisecond (48,000 when using 48MHz Clock)
+#define SYSTICK_ONE_MILLISECOND ((uint32_t)FUNCONF_SYSTEM_CORE_CLOCK / 1000)
+// Number of ticks elapsed per microsecond (48 when using 48MHz Clock)
+#define SYSTICK_ONE_MICROSECOND ((uint32_t)FUNCONF_SYSTEM_CORE_CLOCK / 1000000)
+
+// Simple macro functions to give a arduino-like functions to call
+// millis() reads the incremented systick variable
+// micros() reads the raw SysTick Count, and divides it by the number of
+// ticks per microsecond ( WARN: Wraps every 90 seconds!)
+#define millis() (systick_millis)
+#define micros() (SysTick->CNT / SYSTICK_ONE_MICROSECOND)
+
+// Incremented in the SysTick IRQ - in this example once per millisecond
+extern volatile uint32_t systick_millis;
+
+// Function declarations
+void systick_init(void);
+void SysTick_Handler(void) __attribute__((interrupt));
+
+#endif  // SYSTICK_H