From 86af4e6680b6a3607c76ef7c944897fce85e3a3d Mon Sep 17 00:00:00 2001
From: 94xhn <87560781+94xhn@users.noreply.github.com>
Date: Sat, 11 Jul 2026 23:28:02 +0800
Subject: [PATCH] fix(HardwareTimer): use ARR+1 in getCaptureCompare
 percent/resolution

getCaptureCompare() divided by LL_TIM_GetAutoReload() (ARR) for
PERCENT_COMPARE_FORMAT and all RESOLUTION_xB_COMPARE_FORMAT cases,
while its counterpart setCaptureCompare() multiplies by ARR+1, per
the code's own comment: "PWM reach 100% with CCRx value strictly
greater than ARR (So ARR+1 in our case)".

This makes get/set inconsistent: reading back a duty cycle written
via setCaptureCompare(ch, 100, PERCENT_COMPARE_FORMAT) does not
return 100, and overshoots more as ARR gets smaller (e.g. ARR=9
reads back 111, ARR=1 reads back 200). When ARR is 0 (a reachable
state, e.g. after setOverflow(1, TICK_FORMAT)), the getter performs
a division by zero.

Use ARR+1 in the getter too, matching the setter and its own
documented rationale.

Signed-off-by: 94xhn <87560781+94xhn@users.noreply.github.com>
---
 libraries/SrcWrapper/src/HardwareTimer.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libraries/SrcWrapper/src/HardwareTimer.cpp b/libraries/SrcWrapper/src/HardwareTimer.cpp
index 5c88223e21..8c4fe21f45 100644
--- a/libraries/SrcWrapper/src/HardwareTimer.cpp
+++ b/libraries/SrcWrapper/src/HardwareTimer.cpp
@@ -1188,8 +1188,11 @@ uint32_t HardwareTimer::getCaptureCompare(uint32_t channel,  TimerCompareFormat_
     case HERTZ_COMPARE_FORMAT:
       return_value = (uint32_t)(getTimerClkFreq() / (CCR_RegisterValue  * Prescalerfactor));
       break;
+    // As per Reference Manual PWM reach 100% with CCRx value strictly greater than ARR
+    // (So ARR+1 in our case). Use the same ARR+1 "full scale" as setCaptureCompare()
+    // so that get/set are consistent, and to avoid a divide by zero when ARR is 0.
     case PERCENT_COMPARE_FORMAT:
-      return_value = (CCR_RegisterValue * 100) / LL_TIM_GetAutoReload(_timerObj.instance);
+      return_value = (CCR_RegisterValue * 100) / (LL_TIM_GetAutoReload(_timerObj.instance) + 1);
       break;
     case RESOLUTION_1B_COMPARE_FORMAT:
     case RESOLUTION_2B_COMPARE_FORMAT:
@@ -1207,7 +1210,7 @@ uint32_t HardwareTimer::getCaptureCompare(uint32_t channel,  TimerCompareFormat_
     case RESOLUTION_14B_COMPARE_FORMAT:
     case RESOLUTION_15B_COMPARE_FORMAT:
     case RESOLUTION_16B_COMPARE_FORMAT:
-      return_value = (CCR_RegisterValue * ((1 << format) - 1)) / LL_TIM_GetAutoReload(_timerObj.instance);
+      return_value = (CCR_RegisterValue * ((1 << format) - 1)) / (LL_TIM_GetAutoReload(_timerObj.instance) + 1);
       break;
     case TICK_COMPARE_FORMAT:
     default :