Posted on June 25, 2011 at 02:08Hello!
Have you attempted to use two stop bits in transmission from this processor family and seen it work?
Yes, I took a look at my test project and saw, I was also using USART3 on STM32F103RC for DMX packet sending in DMA mode.
My USART init structure is (to use with the ST peripheral library):
static const USART_InitTypeDef
USART_InitStructure = {
DMX_BAUD_RATE,
USART_WordLength_8b,
USART_StopBits_2,
USART_Parity_No,
USART_Mode_Tx,
USART_HardwareFlowControl_None
};
The USART3 ISR processes the first interrupt on TC flag after BREAK has been sent (I use a lot of macros to access registers but they have self explaining names):
/******************************************************************************/
//
// DMX SENDER UART IRQ Handler: on TC only!
// If entered while low baud rate, BREAK complete, - start DMA
// else the last byte sent, - restart packet.
//
/******************************************************************************/
void DMX_USART_IRQHandler(
void)
{
USART_TCIE_CLEAR(DMX_USART); // disable USART TC interrupt
if (DMX_USART->BRR != _BRR) { // low speed: BREAK gone
_SetBaud(1); // set full baud rate
// see Fig.295, page 787, RM0008, Doc ID 13902 Rev 12,
// for multibyte communication with DMA:
USART_TC_CLEAR(DMX_USART); // clear USART TC flag
DMA_IF_CLEAR_BITS(DMX_USART_DMA,
DMX_DMA_IT_TCx); // clear DMA TC flag
DMA_TCIE_SET(DMX_USART_DMA_C); // enable DMA TC interrupt
DMA_ENABLE (DMX_USART_DMA_C); // transmit bytes via DMA
} else { // ALL BYTES sent, start again
NVIC_SetPriority(DMX_USART_IRQn, LOWEST_IT_Priority);
DMX_Sender_Start();
}
}
The DMA ISR looks like:
/******************************************************************************/
//
// DMA Channel IRQ handler
//
// Occures as soon as the last byte moved into USART->DR.
// At this point TXE is still reset, the byte is being transmitted,
// USART TC bit would occure after the STOP bit.
//
// ATTENTION: occures two bytes before! See multibyte communication with DMA
//
/******************************************************************************/
void DMX_DMA_HANDLER(
void) // DMX_USART_DMA_C is responsible for USART TX
{
DMA_TCIE_CLEAR(DMX_USART_DMA_C); // disable DMA TC interrupt
DMX_USART_TCIE_ON; // reenable USART TC interrupt
}
The whole process is started by:
void DMX_Sender_Start(
void)
{
DMX_SendBuffer[1] += 50; // DEBUG SHOW!!!
DMA_DISABLE(DMX_USART_DMA_C); // disable DMA channel
DMA_RELOAD (DMX_USART_DMA_C, (DMX_BUFSIZE+1));// reload DMA channel counter
_SetBaud(2); // set half baud
DMX_USART_TCIE_INIT; // clear USART TC flag, enable its interrupt
USART_PUT_DR(DMX_USART, 0); // send '0'
}
