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AP_ESC_Telem: fix RPM timeout race

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The RPM telemetry data structure can get updated by another thread at
any time. This can cause (now - last_update_us) to be negative, which
looks like the data is nearly UINT32_MAX microseconds stale. To fix
this, we need to use signed integers for the time difference. The
data_valid flag prevents us from accidentally counting extremely stale
data as valid when the signed time difference wraps around, so this
is safe.
This commit is contained in:
Bob Long 2025-01-02 12:13:25 +11:00
parent e1fd90bc6c
commit 6a3a2b40bf
2 changed files with 9 additions and 7 deletions
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12
libraries/AP_ESC_Telem/AP_ESC_Telem.cpp
View File

@ -27,7 +27,7 @@
//#define ESC_TELEM_DEBUG
#define ESC_RPM_CHECK_TIMEOUT_US 210000UL // timeout for motor running validity
#define ESC_RPM_CHECK_TIMEOUT_US 210000L // timeout for motor running validity
extern const AP_HAL::HAL& hal;
@ -202,7 +202,7 @@ bool AP_ESC_Telem::get_rpm(uint8_t esc_index, float& rpm) const
const uint32_t now = AP_HAL::micros();
if (rpm_data_within_timeout(rpmdata, now, ESC_RPM_DATA_TIMEOUT_US)) {
const float slew = MIN(1.0f, (now - rpmdata.last_update_us) * rpmdata.update_rate_hz * (1.0f / 1e6f));
const float slew = constrain_float(int32_t(now - rpmdata.last_update_us) * rpmdata.update_rate_hz * (1.0f / 1e6f), 0, 1);
rpm = (rpmdata.prev_rpm + (rpmdata.rpm - rpmdata.prev_rpm) * slew);
#if AP_SCRIPTING_ENABLED
@ -811,16 +811,18 @@ void AP_ESC_Telem::update()
const uint32_t now_us = AP_HAL::micros();
for (uint8_t i = 0; i < ESC_TELEM_MAX_ESCS; i++) {
// Invalidate RPM data if not received for too long
if ((now_us - _rpm_data[i].last_update_us) > ESC_RPM_DATA_TIMEOUT_US) {
// (last_update_us might be fresher than now_us, so we use a signed difference)
if (int32_t(now_us - _rpm_data[i].last_update_us) > ESC_RPM_DATA_TIMEOUT_US) {
_rpm_data[i].data_valid = false;
}
}
}
bool AP_ESC_Telem::rpm_data_within_timeout(const volatile AP_ESC_Telem_Backend::RpmData &instance, const uint32_t now_us, const uint32_t timeout_us)
bool AP_ESC_Telem::rpm_data_within_timeout(const volatile AP_ESC_Telem_Backend::RpmData &instance, const uint32_t now_us, const int32_t timeout_us)
{
// easy case, has the time window been crossed so it's invalid
if ((now_us - instance.last_update_us) > timeout_us) {
// (last_update_us might be fresher than now_us, so we use a signed difference)
if (int32_t(now_us - instance.last_update_us) > timeout_us) {
return false;
}
// we never got a valid data, to it's invalid

4
libraries/AP_ESC_Telem/AP_ESC_Telem.h
View File

@ -13,7 +13,7 @@
static_assert(ESC_TELEM_MAX_ESCS > 0, "Cannot have 0 ESC telemetry instances");
#define ESC_TELEM_DATA_TIMEOUT_MS 5000UL
#define ESC_RPM_DATA_TIMEOUT_US 1000000UL
#define ESC_RPM_DATA_TIMEOUT_US 1000000L
class AP_ESC_Telem {
public:
@ -134,7 +134,7 @@ public:
private:
// helper that validates RPM data
static bool rpm_data_within_timeout (const volatile AP_ESC_Telem_Backend::RpmData &instance, const uint32_t now_us, const uint32_t timeout_us);
static bool rpm_data_within_timeout (const volatile AP_ESC_Telem_Backend::RpmData &instance, const uint32_t now_us, const int32_t timeout_us);
static bool was_rpm_data_ever_reported (const volatile AP_ESC_Telem_Backend::RpmData &instance);
#if AP_EXTENDED_DSHOT_TELEM_V2_ENABLED