MSP430I2040 EVM Serial Problem

Andrew,

I don't know the functions UARTCharPut and UARTCharGet, so I don't know how they are working. In general you can, even have to send one byte at a time. It now depends on the function if your code works. If UARTCharPut has a wait function that checks if the transmit buffer is empty before writing another byte into it, then it is OK. If this check isn't integrated, then it will definitely not work because you are overwriting the previous byte again and again, never having one transmitted completely with exception of the last one.

Same for the receive function. You are using a for-loop. If the UARTCharGet has a test-function for a received char, then it will work, otherwise you are returning the same byte over and over again. But: This method isn't a good one - on the one hand you waste a lot of time waiting for an incoming byte doing nothing. This means your program stucks in there until all 32 bytes were received and it cannot do anything else. On the other hand your program will stuck in there forever if only one byte gets lost because you won't reach the 32 anymore.

So yes: Interrupts are made for that! So you should use them. How to set them up properly is shown in various code examples from TI. Create a receive buffer that is filled inside an ISR, setting a flag when 32 bytes were received. In addition think about timeouts for broken messages or things like that. Same for transmitting: Let interrupts send your data so your program can do other things in between the slow UART communication.

Dennis

Thank you Dennis,

The uart functions are directly from the CC3200 SDK uart_demo. They do wait for space to send and wait until a byte is received, I will post them below. You are correct about my method for receiving, I will modify this to show me any single byte that is received without waiting for the rest of the frame since at this stage I just wanted to prove that i could communicate with the MSP430I2040.

In a datasheet for the MSP430I2040 EVM (SLAA638) the end of frame and checksum are described; "The end of the frame is a check sum byte, which is a modulus 256 byte sum of each byte from the beginning of the header to the end of the data field followed by an end of frame marker 0x16." Am I calculating this correctly? For the frame I tried to send I calculated the checksum as follows;

unsigned char ChecksumCMD = 0;
ChecksumCMD = (0x68+0x99+0x99+0x99+0x99+0x99+0x99+0x68+0x23+0x02+0x52+0x00);
//This takes the lowest byte of the addition which should be the same as doing the modulus as below,

unsigned int Checksum2CMD = 0;
Checksum2CMD = (0x68+0x99+0x99+0x99+0x99+0x99+0x99+0x68+0x23+0x02+0x52+0x00)%256;

Here are the UART functions

//*****************************************************************************
void
UARTCharPut(unsigned long ulBase, unsigned char ucData)
{
//
// Check the arguments.
//
ASSERT(UARTBaseValid(ulBase));

//
// Wait until space is available.
//
while(HWREG(ulBase + UART_O_FR) & UART_FR_TXFF)
{
}

//
// Send the char.
//
HWREG(ulBase + UART_O_DR) = ucData;
}

//*****************************************************************************
long
UARTCharGet(unsigned long ulBase)
{
//
// Check the arguments.
//
ASSERT(UARTBaseValid(ulBase));

//
// Wait until a char is available.
//
while(HWREG(ulBase + UART_O_FR) & UART_FR_RXFE)
{
}

//
// Now get the char.
//
return(HWREG(ulBase + UART_O_DR));
}

//*****************************************************************************

A modulo 256 checksum is just adding all values together, storing the result into a 8 bit variable. The overflow does the rest for you.

So you should check if

UARTCharPut(UARTA1_BASE, 0x68); 104
UARTCharPut(UARTA1_BASE, 0x99); 104 + 153 = 257 -> 1
UARTCharPut(UARTA1_BASE, 0x99); 1   + 153 = 154
UARTCharPut(UARTA1_BASE, 0x99); 154 + 153 = 307 -> 51
UARTCharPut(UARTA1_BASE, 0x99); 51  + 153 = 204
UARTCharPut(UARTA1_BASE, 0x99); 204 + 153 = 357 -> 101
UARTCharPut(UARTA1_BASE, 0x99); 101 + 153 = 254
UARTCharPut(UARTA1_BASE, 0x68); 254 + 104 = 358 -> 102
UARTCharPut(UARTA1_BASE, 0x23); 102 + 35  = 137
UARTCharPut(UARTA1_BASE, 0x02); 137 + 2   = 139
UARTCharPut(UARTA1_BASE, 0x52); 139 + 82  = 221
UARTCharPut(UARTA1_BASE, 0x00); 221 + 0   = 221

results in

Checksum2CMD = 221

(I hope I didn't do a mistake)

Your functions look like they are waiting for something, yes, although I don't know this style of register access

while( HWREG(ulBase + UART_O_FR) & UART_FR_TXFF ) {}

So does this one

while( HWREG(ulBase + UART_O_FR) & UART_FR_RXFE ) {}

mean it is waiting for the RX-flag to be set?

Dennis

Dennis