ARM LPC1768 UART0 configuration, wrong baud rate
My baud rate should be 115200, but it is 892.9
void UART0_Init(int pclk, int baudrate)
{
unsigned long int DLest;
//unsigned long int pclk;
unsigned int temp;
// Turn on power to UART0
SC->PCONP |= PCUART0_POWERON;
// Set PINSEL0 so that P0.2 = TXD0, P0.3 = RXD0
PINCON->PINSEL0 = (PINCON->PINSEL0 & ~0xf0) | (1 << 4) | (1 << 6);
UART0->LCR = 0x83; // 8 bits, no Parity, 1 Stop bit, DLAB=1
DLest = (pclk / 16) / baudrate; // Set baud rate
UART0->DLM = DLest / 256;
UART0->DLL = DLest % 256;
// UART0->FDR =
UART0->IER = 0x7; //enable RBR (b0), THRE(b1), RLS(b2)
UART0->LCR = 0x03; // 8 bits, no Parity, 1 Stop bit DLAB = 0
UART0->FCR = 0x07; // Enable and reset TX and RX FIFO
}
void prvSetupHardware( void )
{
/* Disable peripherals power. */
SC->PCONP = 0;
/* Enable GPIO power. */
SC->PCONP = PCONP_PCGPIO;
/* Disable TPIU. */
PINCON->PINSEL10 = 0;
if ( SC->PLL0STAT & ( 1 << 25 ) )
{
/* Enable PLL, disconnected. */
SC->PLL0CON = 1;
SC->PLL0FEED = PLLFEED_FEED1;
SC->PLL0FEED = PLLFEED_FEED2;
}
/* Disable PLL, disconnected. */
SC->PLL0CON = 0;
SC->PLL0FEED = PLLFEED_FEED1;
SC->PLL0FEED = PLLFEED_FEED2;
/* Enable main OSC. */
SC->SCS |= 0x20;
while( !( SC->SCS & 0x40 ) );
/* select main OSC, 12MHz, as the PLL clock source. */
SC->CLKSRCSEL = 0x1;
SC->PCLKSEL0 = 0xAAAAAAAA; /* PCLK is 1/2 CCLK */
SC->PCLKSEL1 = 0xAAAAAAAA;
/*Fcc0 = 400MHz, M = 50, N = 3*/
SC->PLL0CFG = 0x20031;
SC->PLL0FEED = PLLFEED_FEED1;
SC->PLL0FEED = PLLFEED_FEED2;
/* Enable PLL, disconnected. */
SC->PLL0CON = 1;
SC->PLL0FEED = PLLFEED_FEED1;
SC->PLL0FEED = PLLFEED_FEED2;
/* Set clock divider. */
/*Clock = 100MHz, Fcc0 = 400MHz*/
SC->CCLKCFG = 0x03;//divided by 4.
/* Configure flash accelerator. */
SC->FLASHCFG = 0x403a;
/* Check lock bit status. */
while( ( ( SC->PLL0STAT & ( 1 << 26 ) ) == 0 ) );
/* Enable and connect. */
SC->PLL0CON = 3;
SC->PLL0FEED = PLLFEED_FEED1;
SC->PLL0FEED = PLLFEED_FEED2;
while( ( ( SC->PLL0STAT & ( 1 << 25 ) ) == 0 ) );
/* Configure the clock for the USB. */
if( SC->PLL1STAT & ( 1 << 9 ) )
{
/* Enable PLL, disconnected. */
SC->PLL1CON = 1;
SC->PLL1FEED = PLLFEED_FEED1;
SC->PLL1FEED = PLLFEED_FEED2;
}
/* Disable PLL, disconnected. */
SC->PLL1CON = 0;
SC->PLL1FEED = PLLFEED_FEED1;
SC->PLL1FEED = PLLFEED_FEED2;
SC->PLL1CFG = 0x23;
SC->PLL1FEED = PLLFEED_FEED1;
SC->PLL1FEED = PLLFEED_FEED2;
/* Enable PLL, disconnected. */
SC->PLL1CON = 1;
SC->PLL1FEED = PLLFEED_FEED1;
SC->PLL1FEED = PLLFEED_FEED2;
while( ( ( SC->PLL1STAT & ( 1 << 10 ) ) == 0 ) );
/* Enable and connect. */
SC->PLL1CON = 3;
SC->PLL1FEED = PLLFEED_FEED1;
SC->PLL1FEED = PLLFEED_FEED2;
while( ( ( SC->PLL1STAT & ( 1 << 9 ) ) == 0 ) );
/* Configure the LEDs. */
vParTestInitialise();
/*pclk = 100MHZ/2, baud = 115200 */
UART0_Init(100000000/2, 115200);
/* Set the sleep mode to highest level sleep*/
SC->PCON = 0x0;
SCB->SCR = 0x0;
/*set push button interrupt */
PINCON->PINSEL4 |= 0x00100000;
SC->EXTMODE =0;
NVIC_SetPriority( EINT0_IRQn, configUIButton1_INTERRUPT_PRIORITY );
NVIC_EnableIRQ( EINT0_IRQn );
NVIC_SetPriority( UART0_IRQn, configUIButton1_INTERRUPT_PRIORITY + 1 );
NVIC_EnableIRQ( UART0_IRQn );
}
I have confirmed that my cclk is running at 100MHz.
I replace the UART init code with code from an example project by Kunil (uart_interrupt_demo):
void uart_init(int baudrate) {
int errorStatus = -1; //< Failure
long int SystemFrequency = 100000000;
// UART clock (FCCO / PCLK_UART0)
unsigned int uClk = SystemFrequency / 4;
unsigned int calcBaudrate = 0;
unsigned int temp = 0;
unsigned int mulFracDiv, dividerAddFracDiv;
unsigned int divider = 0;
unsigned int mulFracDivOptimal = 1;
unsigned int dividerAddOptimal = 0;
unsigned int dividerOptimal = 0;
unsigned int relativeError = 0;
unsigned int relativeOptimalError = 100000;
// Turn on power to UART0
SC->PCONP |= PCUART0_POWERON;
// Change P0.2 and P0.3 mode to TXD0 and RXD0
PINCON->PINSEL0 = (1 << 4) | (1 << 6);
// Set 8N1 mode
UART0->LCR = 0x83;
// Set the baud rate
uClk = uClk >> 4; /* div by 16 */
/*
* The formula is :
* BaudRate= uClk * (mulFracDiv/(mulFracDiv+dividerAddFracDiv) / (16 * DLL)
*/
/*
* The value of mulFracDiv and dividerAddFracDiv should comply to the following expressions:
* 0 < mulFracDiv <= 15, 0 <= dividerAddFracDiv <= 15
*/
for (mulFracDiv = 1; mulFracDiv <= 15; mulFracDiv++) {
for (dividerAddFracDiv = 0; dividerAddFracDiv <= 15; dividerAddFracDiv++) {
temp = (mulFracDiv * uClk) / (mulFracDiv + dividerAddFracDiv);
divider = temp / baudrate;
if ((temp % baudrate) > (baudrate / 2))
divider++;
if (divider > 2 && divider < 65536) {
calcBaudrate = temp / divider;
if (calcBaudrate <= baudrate) {
relativeError = baudrate - calcBaudrate;
} else {
relativeError = calcBaudrate - baudrate;
}
if (relativeError < relativeOptimalError) {
mulFracDivOptimal = mulFracDiv;
dividerAddOptimal = dividerAddFracDiv;
dividerOptimal = divider;
relativeOptimalError = relativeError;
if (relativeError == 0)
break;
}
}
}
if (relativeError == 0)
break;
}
if (relativeOptimalError
< ((baudrate * UART_ACCEPTED_BAUDRATE_ERROR) / 100)) {
UART0->LCR |= DLAB_ENABLE;
UART0->DLM = (unsigned char) ((dividerOptimal >> 8) & 0xFF);
UART0->DLL = (unsigned char) dividerOptimal;
UART0->LCR &= ~DLAB_ENABLE;
UART0->FDR = ((mulFracDivOptimal << 4) & 0xF0) | (dividerAddOptimal
& 0x0F);
errorStatus = 0; //< Success
}
// Enable TX and RX FIFO
UART0->FCR |= FIFO_ENABLE;
// Set FIFO to trigger when at least 14 characters available
UART0->FCR |= (3 << 6);
// Enable UART RX interrupt (for LPC17xx UART)
UART0->IER = RBR_IRQ_ENABLE;
// Enable the UART interrupt (for Cortex-CM3 NVIC)
NVIC_EnableIRQ(UART0_IRQn);
}
And it works!
I have to go through and see what i had wrong. I suspect the order of register settings was off.
Answer
Have a look at the Errata sheet.
You can't set SC->PCLKSEL0 after you fired up the main PLL, so the divider stays at CCLK/4.
Just move the line
/* Setup the peripheral bus to be the same as the PLL output (64 MHz). */
SC->PCLKSEL0 = 0x05555555;
a few lines up, before you enable the PLL.