MSP430F5419A: How to implement interrupt driven UART transmit?

Derek

Part Number: MSP430F5419A

Hello,

I have a product where we need to send a string to a slow serial peripheral (9600 baud) and the messages can be about 100 bytes at a time. I currently have this working tx function:

unsigned int i, len;
len = strlen(_ptr);
for(i=0 ; i<len ; i++)
{
while(!(UCA2IFG&UCTXIFG));
UCA2TXBUF = (unsigned char) _ptr[i];
}
while(UCA2STAT&UCBUSY);

However, since the baud rate is slow, this causes the CPU to spend a lot of time waiting. What is the best way to change this to an interrupt driven routine, or something to unburden the CPU?

Thanks,

Derek

over 1 year ago

0 JD Crutchfield over 1 year ago

TI__Mastermind 27250 points

Hey Derek,

There is some example code in TI Resource explorer.

This is a UART Echo at 9600: https://dev.ti.com/tirex/explore/node?node=A__AGLj99bhfJ8Z15Jhh5LvSQ__msp430ware__IOGqZri__LATEST&placeholder=true

There is also a bit more complex UART transceiver example: https://dev.ti.com/tirex/explore/node?node=A__ACwWKW7sUJopiD6YeXP4dg__msp430ware__IOGqZri__LATEST&placeholder=true

Both of these interrupt off the RX flag, but in your case, you probably need to modify these to actually interrupt off the TX flag to just send the next byte.

Hope these help.

0 David Schultz over 1 year ago in reply to JD Crutchfield

Guru 19685 points

The examples are kind of useless, really.

There are three things needed. The first is a data structure to hold the data. I like a FIFO queue. Two routines are needed, one to insert a byte into the queue. (This should block and wait for space to open up if the queue is full.) A second to return a 16 bit integer. Which holds the data byte if available or -1 if no data is available.

Next is the transmit interrupt service routine. If more data is available in the queue, get it and put it in TXBUF. Otherwise clear TXIE.

Then there is the foreground transmit routine. This inserts data into the queue and then sets TXIE.

This assumes you never ever read UCAIV. Which clears interrupt requests in a way that makes this more difficult.

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MSP430F5419A: How to implement interrupt driven UART transmit?