embed/trezorhal: simplify systick, remove microsecond precision

embed/trezorhal/systick.c

@@ -90,51 +90,10 @@ void mp_hal_delay_us(mp_uint_t usec) {
     }
 }
 
-bool sys_tick_has_passed(uint32_t start_tick, uint32_t delay_ms) {
-    return HAL_GetTick() - start_tick >= delay_ms;
-}
-
-// waits until at least delay_ms milliseconds have passed from the sampling of
-// startTick. Handles overflow properly. Assumes stc was taken from
-// HAL_GetTick() some time before calling this function.
-void sys_tick_wait_at_least(uint32_t start_tick, uint32_t delay_ms) {
-    while (!sys_tick_has_passed(start_tick, delay_ms)) {
-        __WFI(); // enter sleep mode, waiting for interrupt
-    }
-}
-
 mp_uint_t mp_hal_ticks_ms(void) {
     return uwTick;
 }
 
-// The SysTick timer counts down at 168 MHz, so we can use that knowledge
-// to grab a microsecond counter.
-//
-// We assume that HAL_GetTickis returns milliseconds.
 mp_uint_t mp_hal_ticks_us(void) {
-    mp_uint_t irq_state = disable_irq();
-    uint32_t counter = SysTick->VAL;
-    uint32_t milliseconds = HAL_GetTick();
-    uint32_t status  = SysTick->CTRL;
-    enable_irq(irq_state);
-
-    // It's still possible for the countflag bit to get set if the counter was
-    // reloaded between reading VAL and reading CTRL. With interrupts  disabled
-    // it definitely takes less than 50 HCLK cycles between reading VAL and
-    // reading CTRL, so the test (counter > 50) is to cover the case where VAL
-    // is +ve and very close to zero, and the COUNTFLAG bit is also set.
-    if ((status & SysTick_CTRL_COUNTFLAG_Msk) && counter > 50) {
-        // This means that the HW reloaded VAL between the time we read VAL and the
-        // time we read CTRL, which implies that there is an interrupt pending
-        // to increment the tick counter.
-        milliseconds++;
-    }
-    uint32_t load = SysTick->LOAD;
-    counter = load - counter; // Convert from decrementing to incrementing
-
-    // ((load + 1) / 1000) is the number of counts per microsecond.
-    //
-    // counter / ((load + 1) / 1000) scales from the systick clock to microseconds
-    // and is the same thing as (counter * 1000) / (load + 1)
-    return milliseconds * 1000 + (counter * 1000) / (load + 1);
+    return uwTick * 1000;
 }