qemu/mcu/arm: Implement a SysTick driver.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

Author: iabdalkader

ports/qemu/Makefile

@@ -77,6 +77,7 @@ LIBS = $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
 SRC_C += \
 	mcu/arm/errorhandler.c \
 	mcu/arm/startup.c \
+	mcu/arm/ticks.c \
 	shared/runtime/semihosting_arm.c \
 
 endif

ports/qemu/mcu/arm/errorhandler.c

@@ -191,7 +191,7 @@ __attribute__((naked)) MP_NORETURN void PendSV_Handler(void) {
     exception_handler(PENDING_SV);
 }
 
-__attribute__((naked)) MP_NORETURN void SysTick_Handler(void) {
+__attribute__((naked, weak)) MP_NORETURN void SysTick_Handler(void) {
     exception_handler(SYSTEM_TICK);
 }
 

ports/qemu/mcu/arm/startup.c

@@ -118,6 +118,9 @@ const uint32_t isr_vector[] __attribute__((section(".isr_vector"))) = {
 void _start(void) {
     mp_semihosting_init();
 
+    extern void ticks_init(void);
+    ticks_init();
+
     // Enable the UART
     uart_init();
 

ports/qemu/mcu/arm/ticks.c

@@ -0,0 +1,85 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2025 Ibrahim Abdelkader <iabdalkader@openmv.io>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+
+// CPU frequency
+#ifndef CPU_FREQ_HZ
+#define CPU_FREQ_HZ             25000000u
+#endif
+
+// SysTick registers
+#define SYSTICK_BASE            0xE000E010
+#define SYSTICK_CSR             (*(volatile uint32_t *)(SYSTICK_BASE + 0x00))
+#define SYSTICK_RVR             (*(volatile uint32_t *)(SYSTICK_BASE + 0x04))
+#define SYSTICK_CVR             (*(volatile uint32_t *)(SYSTICK_BASE + 0x08))
+
+// SysTick config bits
+#define SYSTICK_CSR_ENABLE      (1 << 0)
+#define SYSTICK_CSR_TICKINT     (1 << 1)
+#define SYSTICK_CSR_CLKSOURCE   (1 << 2)
+
+static volatile uint32_t _ticks_ms = 0;
+#if defined(__ARM_ARCH_ISA_ARM)
+static volatile uint32_t _ticks_us = 0;
+#endif
+
+void ticks_init(void) {
+    #if !defined(__ARM_ARCH_ISA_ARM)
+    // Configure SysTick: reload at 1ms intervals (Cortex-M)
+    SYSTICK_CVR = 0;
+    SYSTICK_RVR = (CPU_FREQ_HZ / 1000) - 1;
+    SYSTICK_CSR = SYSTICK_CSR_ENABLE | SYSTICK_CSR_TICKINT | SYSTICK_CSR_CLKSOURCE;
+    #endif
+}
+
+uintptr_t ticks_ms(void) {
+    #if defined(__ARM_ARCH_ISA_ARM)
+    return _ticks_us++ / 1000;
+    #else
+    return _ticks_ms;
+    #endif
+}
+
+uintptr_t ticks_us(void) {
+    #if defined(__ARM_ARCH_ISA_ARM)
+    return _ticks_us++;
+    #else
+    // Get current values atomically
+    uint32_t ms = _ticks_ms;
+    uint32_t cvr = SYSTICK_CVR;
+
+    // Calculate microseconds from the down-counter
+    uint32_t elapsed_cycles = SYSTICK_RVR - cvr;
+    uint32_t us_fraction = (elapsed_cycles * 1000) / (CPU_FREQ_HZ / 1000);
+
+    return (ms * 1000) + us_fraction;
+    #endif
+}
+
+void SysTick_Handler(void) {
+    _ticks_ms++;
+}