Hi,
I'm programming an MSP430F5325, using Code Composer Studio and interfacing by way of the programming half of a Launchpad board that is connected to the spy-by-wire pins. My goal is simply to send UART data out the UCA0TXD line at a reasonably fast baud rate like 115K. While I'm basically having success, I'm finding that there seems to be a time lag of about .3 ms between each byte, and I haven't spotted in the docs any explanation about why this is or whether it's possible to eliminate it. The following output from my logic analyzer illustrates what's happening:
Here's the basic code I've been using:
#include "msp430f5325.h"
void main(void) {
WDTCTL = WDTPW + WDTHOLD; // Stop WDT
// Setup clocks.
UCSCTL1 = DCORSEL_5; // Select basic DCO clock range (~2-54 MHz)
UCSCTL2 = 488; // DCO = REFOCLK * 488 (32,768 * 488 = ~16 MHz)
UCSCTL3 = SELREF_2;
UCSCTL4 = SELA_3 | SELS_3; // ACLK = SMCLK = DCOCLK
// Setup USCI for 115 kbaud UART.
P3SEL |= BIT3; // P3.3=UCA0TXD
UCA0CTL1 |= UCSSEL_2; // SMCLK = source for baud rate generation
UCA0BR0 = 138; // SMCLK 16MHz => 115k baud (see MSP430x5xx Family User's Guide table 34-4)
UCA0BR1 = 0; // SMCLK 16MHz => 115k baud
UCA0MCTL = UCBRS_7; // SMCLK 16MHz => 115k baud (Modulation UCBRSx = 7)
UCA0CTL1 &= ~UCSWRST; // **Initialize USCI state machine**
// Main loop.
int j = 0;
while (1) {
while (!(UCA0IFG & UCTXIFG)) ;
UCA0TXBUF = j++;
}
}
I've tried both polling (as shown here) and also interrupts in order to get transmitted the second and subsequent bytes. I've messed around with a number of other options, but have yet to eliminate the long idle period, which as you can see slows down the overall bandwidth of the transmission quite a bit (by about a factor of 3). Thanks in advance for any suggestions!
Christopher
