From a51286396fd480656b56c728c2f702e18c02aac7 Mon Sep 17 00:00:00 2001
From: 94xhn <87560781+94xhn@users.noreply.github.com>
Date: Sat, 11 Jul 2026 23:45:23 +0800
Subject: [PATCH] fix(HardwareTimer): guard HERTZ_FORMAT get* against
 register==0

getCount(HERTZ_FORMAT) and getCaptureCompare(..., HERTZ_COMPARE_FORMAT)
both compute getTimerClkFreq() / (register * Prescalerfactor), dividing
directly by the live CNT (counter) or CCR (capture/compare) hardware
register with no zero-guard.

Both registers legitimately read 0 with no caller error involved:
- CNT is 0 right at/after every timer reset or overflow, simply from
  the timer running (getOverflow()/setOverflow() already special-case
  this exact situation via the ARR+1 "period" offset; getCount() and
  getCaptureCompare() do not).
- CCR is 0 on reset before the first setCaptureCompare() call, and in
  Input Capture mode holds whatever was last captured, which is 0
  before any edge has been captured or if an edge lands exactly at
  CNT == 0.

Hitting either case triggers an integer divide by zero: undefined
behavior in C/C++, verified to crash (SIGFPE-equivalent) on a desktop
toolchain. On Cortex-M without DIV_0_TRP configured (the default),
UDIV silently returns 0, so on-target this instead silently reports
"0 Hz" with no indication anything went wrong.

Add an explicit zero-check to both HERTZ_FORMAT branches, returning 0
(no meaningful frequency available) instead of dividing, matching the
existing "do not underflow" zero-guard style already used by
setOverflow() in this same file. No public API/signature changes.

Signed-off-by: 94xhn <87560781+94xhn@users.noreply.github.com>
---
 libraries/SrcWrapper/src/HardwareTimer.cpp | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/libraries/SrcWrapper/src/HardwareTimer.cpp b/libraries/SrcWrapper/src/HardwareTimer.cpp
index 5c88223e21..4f832a1ea0 100644
--- a/libraries/SrcWrapper/src/HardwareTimer.cpp
+++ b/libraries/SrcWrapper/src/HardwareTimer.cpp
@@ -729,7 +729,10 @@ uint32_t HardwareTimer::getCount(TimerFormat_t format)
       return_value = (uint32_t)((CNT_RegisterValue * Prescalerfactor * 1000000.0) / getTimerClkFreq());
       break;
     case HERTZ_FORMAT:
-      return_value = (uint32_t)(getTimerClkFreq() / (CNT_RegisterValue  * Prescalerfactor));
+      // CNT_RegisterValue is 0 right at/after every timer reset or overflow,
+      // which is a normal, reachable state (not a caller error): avoid a
+      // divide by zero and report 0 (no meaningful frequency available).
+      return_value = (CNT_RegisterValue == 0) ? 0 : (uint32_t)(getTimerClkFreq() / (CNT_RegisterValue * Prescalerfactor));
       break;
     case TICK_FORMAT:
     default :
@@ -1186,7 +1189,12 @@ uint32_t HardwareTimer::getCaptureCompare(uint32_t channel,  TimerCompareFormat_
       return_value = (uint32_t)((CCR_RegisterValue * Prescalerfactor * 1000000.0) / getTimerClkFreq());
       break;
     case HERTZ_COMPARE_FORMAT:
-      return_value = (uint32_t)(getTimerClkFreq() / (CCR_RegisterValue  * Prescalerfactor));
+      // CCR_RegisterValue is 0 on reset (before the first setCaptureCompare()
+      // call) and, in Input Capture mode, whenever the last captured edge
+      // landed exactly at CNT == 0 or before any edge has been captured yet.
+      // That is a normal, reachable state (not a caller error): avoid a
+      // divide by zero and report 0 (no meaningful frequency available).
+      return_value = (CCR_RegisterValue == 0) ? 0 : (uint32_t)(getTimerClkFreq() / (CCR_RegisterValue * Prescalerfactor));
       break;
     case PERCENT_COMPARE_FORMAT:
       return_value = (CCR_RegisterValue * 100) / LL_TIM_GetAutoReload(_timerObj.instance);