The normal HAL library is not useful for continuous reception or commands with different length.
If you have the complete HAL package installed, you could look at the examples for the LowLevel interface.
Projects\STM32F411RE-Nucleo\Examples_LL\USART\USART_Communication_Rx_IT_Continuous
The main thing is to set you usart to continuous reception:
void Configure_USART(void) {
/* (1) Enable GPIO clock and configures the USART pins *********************/
/* Enable the peripheral clock of GPIO Port */
USARTx_GPIO_CLK_ENABLE();
/* Configure Tx Pin as : Alternate function, High Speed, Push pull, Pull up */
LL_GPIO_SetPinMode(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_MODE_ALTERNATE);
USARTx_SET_TX_GPIO_AF();
LL_GPIO_SetPinSpeed(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_SPEED_FREQ_HIGH);
LL_GPIO_SetPinOutputType(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
LL_GPIO_SetPinPull(USARTx_TX_GPIO_PORT, USARTx_TX_PIN, LL_GPIO_PULL_UP);
/* Configure Rx Pin as : Alternate function, High Speed, Push pull, Pull up */
LL_GPIO_SetPinMode(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_MODE_ALTERNATE);
USARTx_SET_RX_GPIO_AF();
LL_GPIO_SetPinSpeed(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_SPEED_FREQ_HIGH);
LL_GPIO_SetPinOutputType(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
LL_GPIO_SetPinPull(USARTx_RX_GPIO_PORT, USARTx_RX_PIN, LL_GPIO_PULL_UP);
/* (2) NVIC Configuration for USART interrupts */
/* - Set priority for USARTx_IRQn */
/* - Enable USARTx_IRQn */
NVIC_SetPriority(USARTx_IRQn, 0);
NVIC_EnableIRQ(USARTx_IRQn);
/* (3) Enable USART peripheral clock and clock source ***********************/
USARTx_CLK_ENABLE();
/* (4) Configure USART functional parameters ********************************/
/* TX/RX direction */
LL_USART_SetTransferDirection(USARTx_INSTANCE, LL_USART_DIRECTION_TX_RX);
/* 8 data bit, 1 start bit, 1 stop bit, no parity */
LL_USART_ConfigCharacter(USARTx_INSTANCE, LL_USART_DATAWIDTH_8B, LL_USART_PARITY_NONE, LL_USART_STOPBITS_1);
/* No Hardware Flow control */
/* Reset value is LL_USART_HWCONTROL_NONE */
// LL_USART_SetHWFlowCtrl(USARTx_INSTANCE, LL_USART_HWCONTROL_NONE);
/* Oversampling by 16 */
/* Reset value is LL_USART_OVERSAMPLING_16 */
// LL_USART_SetOverSampling(USARTx_INSTANCE, LL_USART_OVERSAMPLING_16);
/* Set Baudrate to 115200 using APB frequency set to 100000000/APB_Div Hz */
/* Frequency available for USART peripheral can also be calculated through LL RCC macro */
/* Ex :
Periphclk = LL_RCC_GetUSARTClockFreq(Instance); or
LL_RCC_GetUARTClockFreq(Instance); depending on USART/UART instance
In this example, Peripheral Clock is expected to be equal to
100000000/APB_Div Hz => equal to SystemCoreClock/APB_Div
*/
LL_USART_SetBaudRate(USARTx_INSTANCE, SystemCoreClock/APB_Div, LL_USART_OVERSAMPLING_16, 115200);
/* (5) Enable USART *********************************************************/
LL_USART_Enable(USARTx_INSTANCE);
}
The USART IT Handler should look like
void USARTx_IRQHandler(void)
{
/* Check RXNE flag value in SR register */
if(LL_USART_IsActiveFlag_RXNE(USARTx_INSTANCE) && LL_USART_IsEnabledIT_RXNE(USARTx_INSTANCE))
{
/* RXNE flag will be cleared by reading of DR register (done in call) */
/* Call function in charge of handling Character reception */
USART_CharReception_Callback();
}
else
{
/* Call Error function */
Error_Callback();
}
}
The last thing to set up is the Callback
void USART_CharReception_Callback(void);
Where you could put the bytes into an buffer and handle it in the main loop or where you want.