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After making a small change to my Timer_A ISR (clearing a flag just before enabling it's corresponding interrupt) I start having issues with data transmission on my UART. I'm trying to understand what is going on here.
The line added to my Timer_A ISR which triggers the issues:
CCTL2 &= ~CCIFG;
After some experimentation I found that my homebrew print() function is now sometimes determining the UART transmitter is empty when it shouldn't, and sending a character directly to TXBUF0 when it should be added to my circular buffer. I can work around the issue by checking the TXEPT flag remains set for several cycles but I'm hoping to find a better/more robust solution or an approach that avoids this issue all together. Any ideas or suggestions?
I'm using CCS 6.2.0.00050, targeting an MSP430AFE253 device with Timer_A3 and USART0.
Included below is my code for the UART Tx ISR and print() functions.
#define UART_TX_BUFSIZE (128) // Must be a power of 2
unsigned char uart_tx_buffer[UART_TX_BUFSIZE];
unsigned char uart_tx_buf_widx;
unsigned char uart_tx_buf_ridx;
#pragma vector = USART0TX_VECTOR
__interrupt void USART0_TX(void)
{
if(uart_tx_buf_ridx != uart_tx_buf_widx) // Check if there are any bytes to send
{
TXBUF0 = uart_tx_buffer[uart_tx_buf_ridx]; // Output next byte
uart_tx_buf_ridx = (uart_tx_buf_ridx+1) & (UART_TX_BUFSIZE-1); // Increment & wrap at end of circular buffer
}
}
void printf(char *pstr)
{
if(*pstr == '\0')
return;
// If buffer was empty, fire up the UART to get tx interrupts
if(UTCTL0 & TXEPT) // Transmitter shift register and UxTXBUF are empty or SWRST = 1
TXBUF0 = *pstr++;
while(*pstr != '\0') // Warning : No length limit
{
unsigned char wr_idx_next = (uart_tx_buf_widx+1) & (UART_TX_BUFSIZE-1);
if(wr_idx_next == uart_tx_buf_ridx)
return; // Buffer overflow (discard any remaining chars)
uart_tx_buffer[uart_tx_buf_widx] = *pstr++;
uart_tx_buf_widx = wr_idx_next;
}
}
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