I would like to receive any length of data from USART2 DMA circular mode, then transmit the identical data via USART1 DMA normal mode.

However, I found that there is a probability that even USART2 receives the full data, USART1 will miss to transmit some bytes.

volatile uint8_t RxMsg_USART2_temp[1];
volatile uint8_t RxMsg_USART2[120];
HAL_UART_Receive_DMA(&huart2, RxMsg_USART2_temp, sizeof(RxMsg_USART2_temp));

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart){
    if(huart->Instance == USART2){
        if( RxMsg_USART2_temp[0] != 'n' ){
            RxMsg_USART2[idx] = RxMsg_USART2_temp[0];
            idx++;
        }else{
            RxMsg_USART2[idx] = RxMsg_USART2_temp[0];
            HAL_UART_Transmit_DMA(&huart1, RxMsg_USART2, idx+1);
        }
    }
}

void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart){
    if(huart->Instance == USART1){
        memset(RxMsg_USART2_temp, 0, sizeof(RxMsg_USART2_temp));
        memset(RxMsg_USART2, 0, sizeof(RxMsg_USART2));
        idx = 0;
    }
}