STM32G4 CORDIC HAL Library HAL_CORDIC_Calculate function
Hi,
There would appear to be an error in the HAL_CORDIC_Calculate that results in errors when gcc optimsation O3 is turned on.
I had the following code:
void CORDIC_SineCalcSingleValue(float radiansNorm, float sin)
{
float angle_q31f;
int32_t angle_q31[1];
/* Convert radians normalised over pi to Q31 format */
angle_q31f = radiansNorm * Q_31;
angle_q31[0] = (int32_t)angle_q31f; // Convert to Q31 integer format
int32_t result_q31[1]; // Output array Cos then Sin
/* Calc sine and cos with CORDIC */
if(HAL_CORDIC_Calculate(&hcordic, angle_q31, result_q31, 1, 500) != HAL_OK) /* HAL_MAX_DELAY */
{
// Handle error
return;
}
// /* Compiler barrier to prevent reordering */
// __asm volatile ("" ::: "memory");
sin = (float)result_q31[0] / Q_31; // Convert back to float
}
My theory is the following although nit is probably wrong.
This code fails because the HAL_CORDIC_Calculate argument result_q31 is not specified as volatile by the HAL function so the function is "skipped" and it does not return so the if function always executes the
// Handle Error
return;
when the O3 optimisation is on even though.the function returns HAL_OK By putting a memory barrier in before the sine = ... the HAL_CORDIC_Calculate is forced to fully evaluate in the order written so that is a fix. But the real issue is the HAL_CORDIC_Calculate should use a volatile for the result arg as the compiler seems to miss the fact the variable is modified by code when it reads the output register: It seems to think it is changed by the peripheral directly.
HAL_StatusTypeDef HAL_CORDIC_Calculate(
CORDIC_HandleTypeDef *hcordic,
int32_t *pInBuff,
volatile int32_t *pOutBuff,
uint32_t NbCalc, uint32_t Timeout)
/**
* @brief Read output data of CORDIC processing, and increment output buffer pointer.
* @PAram hcordic pointer to a CORDIC_HandleTypeDef structure that contains
* the configuration information for CORDIC module.
* @PAram ppOutBuff Pointer to pointer to output buffer.
* @retval none
*/
static void CORDIC_ReadOutDataIncrementPtr(const CORDIC_HandleTypeDef *hcordic, int32_t **ppOutBuff)
{
/* First read of output data from the Read Data register */
**ppOutBuff = (int32_t)READ_REG(hcordic->Instance->RDATA);
/* Increment output data pointer */
(*ppOutBuff)++;
/* Check if second read of output data is expected */
if (HAL_IS_BIT_SET(hcordic->Instance->CSR, CORDIC_CSR_NRES))
{
/* Second read of output data from the Read Data register */
**ppOutBuff = (int32_t)READ_REG(hcordic->Instance->RDATA);
/* Increment output data pointer */
(*ppOutBuff)++;
}
}When the function is called the result variable supplied must of course be volatile.
oid CORDIC_SineCalcSingleValue(float radiansNorm, float sin)
{
float angle_q31f;
int32_t angle_q31[1];
/* Convert radians normalised over pi to Q31 format */
angle_q31f = radiansNorm * Q_31;
angle_q31[0] = (int32_t)angle_q31f; // Convert to Q31 integer format
volatile int32_t result_q31[1]; // Output array Cos then Sin
/* Calc sine and cos with CORDIC */
if(HAL_CORDIC_Calculate(&hcordic, angle_q31, result_q31, 1, 500) != HAL_OK) /* HAL_MAX_DELAY */
{
// Handle error
return;
}
sin = (float)result_q31[0] / Q_31; // Convert back to float
}
When the volatile qualifier is used the function works correctly with gcc O3 optimisation.
The entire file for this working code is attached below.
Nay thoughts would be appreciated.