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Check busy bit #21

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fc95b8f
Accelerometer: Wait for EC busy bit and validate sample ID
JohnAZoidberg Mar 1, 2026
12ea959
Accelerometer: Check CrosEcReadMemU8 return values
JohnAZoidberg Mar 1, 2026
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116 changes: 99 additions & 17 deletions FrameworkSensors/AccelerometerClient.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -517,34 +517,115 @@ AccelerometerDevice::GetData(

SENSOR_FunctionEnter();

//
// Read sensor data safely using the EC busy bit and sample ID protocol.
// The EC sets the busy bit while updating sensor data and increments the
// sample ID (lower 4 bits of ACC_STATUS) after each update. We must:
// 1. Wait for the busy bit to clear
// 2. Record the sample ID
// 3. Read all sensor data
// 4. Re-read ACC_STATUS and verify the busy bit is still clear
// and the sample ID hasn't changed
// This guarantees we didn't read partially-updated data.
//
UINT8 acc_status = 0;
CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_STATUS, &acc_status);
TraceInformation("Status: (%02x), Present: %d, Busy: %d\n",
acc_status,
(acc_status & EC_MEMMAP_ACC_STATUS_PRESENCE_BIT) > 0,
(acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) > 0);
UINT8 samp_id = 0xFF;
UINT8 status = 0;
int attempts = 0;

#define quarter (0xFFFF/4)
#define MAX_SENSOR_READ_ATTEMPTS 5
#define MAX_BUSY_WAIT_ATTEMPTS 50
#define BUSY_WAIT_SLEEP_INTERVAL 5
#define BUSY_WAIT_SLEEP_MS 25

// Helper: read a byte from EC memory map, goto Exit on failure.
// Note: CrosEcReadMemU8 already traces its own errors internally.
// We cannot use WPP trace macros inside #define because WPP generates
// per-line identifiers that break when the macro is expanded elsewhere.
#define EC_READ_U8(offset, dest) do { \
if (CrosEcReadMemU8(Handle, (offset), (dest)) == 0) { \
Status = STATUS_IO_DEVICE_ERROR; \
goto Exit; \
} \
} while (0)

UINT8 lid_angle_bytes[2] = {0};
CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 0, &lid_angle_bytes[0]);
CrosEcReadMemU8(Handle, EC_MEMMAP_ACC_DATA + 1, &lid_angle_bytes[1]);
UINT16 lid_angle = lid_angle_bytes[0] + (lid_angle_bytes[1] << 8);
UINT16 lid_angle = 0;
UINT SensorOffset = 6 * m_LidSensorIndex + EC_MEMMAP_ACC_DATA + 2;
UINT8 Sensor1[6] = {0};

while ((status & (EC_MEMMAP_ACC_STATUS_BUSY_BIT |
EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK)) != samp_id) {

if (attempts++ >= MAX_SENSOR_READ_ATTEMPTS) {
TraceError("%!FUNC! Failed to get consistent sensor data after %d attempts", attempts);
Status = STATUS_IO_DEVICE_ERROR;
goto Exit;
}

//
// Poll ACC_STATUS until the EC is not busy
//
int busy_attempts = 0;
EC_READ_U8(EC_MEMMAP_ACC_STATUS, &acc_status);

while (acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) {
if (busy_attempts++ >= MAX_BUSY_WAIT_ATTEMPTS) {
TraceError("%!FUNC! EC busy bit stuck after %d attempts", busy_attempts);
Status = STATUS_IO_DEVICE_ERROR;
goto Exit;
}

if (busy_attempts % BUSY_WAIT_SLEEP_INTERVAL == 0)
Sleep(BUSY_WAIT_SLEEP_MS);

EC_READ_U8(EC_MEMMAP_ACC_STATUS, &acc_status);
}

TraceInformation("Status: (%02x), Present: %d, Busy: %d\n",
acc_status,
(acc_status & EC_MEMMAP_ACC_STATUS_PRESENCE_BIT) > 0,
(acc_status & EC_MEMMAP_ACC_STATUS_BUSY_BIT) > 0);

//
// Record the current sample ID before reading data
//
samp_id = acc_status & EC_MEMMAP_ACC_STATUS_SAMPLE_ID_MASK;

//
// Read all sensor data (unsafe - EC could update mid-read)
//
EC_READ_U8(EC_MEMMAP_ACC_DATA + 0, &lid_angle_bytes[0]);
EC_READ_U8(EC_MEMMAP_ACC_DATA + 1, &lid_angle_bytes[1]);

EC_READ_U8(SensorOffset + 0, &Sensor1[0]);
EC_READ_U8(SensorOffset + 1, &Sensor1[1]);
EC_READ_U8(SensorOffset + 2, &Sensor1[2]);
EC_READ_U8(SensorOffset + 3, &Sensor1[3]);
EC_READ_U8(SensorOffset + 4, &Sensor1[4]);
EC_READ_U8(SensorOffset + 5, &Sensor1[5]);

//
// Re-read ACC_STATUS to verify data consistency
//
EC_READ_U8(EC_MEMMAP_ACC_STATUS, &status);
}

#undef EC_READ_U8

//
// Data is now consistent - process it
//
lid_angle = lid_angle_bytes[0] + (lid_angle_bytes[1] << 8);
TraceInformation("Lid Angle Status: %dDeg%s", lid_angle, lid_angle == 500 ? "(Unreliable)" : "");

// Lid accelerometer is relevant for screen rotation
// Base accelerometer is not used in this driver
// It's only used for lid angle in the EC firmware
UINT SensorOffset = 6 * m_LidSensorIndex + EC_MEMMAP_ACC_DATA + 2;
UINT16 Sensor1[6] = {0};
CrosEcReadMemU8(Handle, SensorOffset, (UINT8*)&Sensor1[0]);
CrosEcReadMemU8(Handle, SensorOffset + 1, (UINT8*)&Sensor1[1]);
CrosEcReadMemU8(Handle, SensorOffset + 2, (UINT8*)&Sensor1[2]);
CrosEcReadMemU8(Handle, SensorOffset + 3, (UINT8*)&Sensor1[3]);
CrosEcReadMemU8(Handle, SensorOffset + 4, (UINT8*)&Sensor1[4]);
CrosEcReadMemU8(Handle, SensorOffset + 5, (UINT8*)&Sensor1[5]);
m_CachedData.Axis.X = (float) (Sensor1[0] + (Sensor1[1] << 8));
m_CachedData.Axis.Y = (float) (Sensor1[2] + (Sensor1[3] << 8));
m_CachedData.Axis.Z = (float) (Sensor1[4] + (Sensor1[5] << 8));
#define quarter (0xFFFF/4)
m_CachedData.Axis.X = -((float) (INT16) m_CachedData.Axis.X) / quarter;
m_CachedData.Axis.Y = -((float) (INT16) m_CachedData.Axis.Y) / quarter;
m_CachedData.Axis.Z = -((float) (INT16) m_CachedData.Axis.Z) / quarter;
Expand Down Expand Up @@ -610,6 +691,7 @@ AccelerometerDevice::GetData(
TraceInformation("COMBO %!FUNC! LAC Data did NOT meet the threshold");
}

Exit:
SENSOR_FunctionExit(Status);
return Status;
}
Expand Down