void spi_frequency(spi_t *obj, int hz) {
uint32_t error = 0;
uint32_t p_error = 0xffffffff;
uint32_t ref = 0;
uint8_t spr = 0;
uint8_t ref_spr = 0;
uint8_t ref_prescaler = 0;
// bus clk
uint32_t PCLK = bus_frequency();
uint8_t prescaler = 1;
uint8_t divisor = 2;
for (prescaler = 1; prescaler <= 8; prescaler++) {
divisor = 2;
for (spr = 0; spr <= 8; spr++, divisor *= 2) {
ref = PCLK / (prescaler*divisor);
if (ref > (uint32_t)hz)
continue;
error = hz - ref;
if (error < p_error) {
ref_spr = spr;
ref_prescaler = prescaler - 1;
p_error = error;
}
}
}
// set SPPR and SPR
obj->spi->BR = ((ref_prescaler & 0x7) << 4) | (ref_spr & 0xf);
}
void spi_frequency(spi_t *obj, int hz) {
uint32_t f_error = 0;
uint32_t p_error = 0xffffffff;
uint32_t ref = 0;
uint32_t br = 0;
uint32_t ref_spr = 0;
uint32_t ref_prescaler = 0;
uint32_t ref_dr = 0;
// bus clk
uint32_t PCLK = bus_frequency();
for (uint32_t i = 0; i < 4; i++) {
for (br = 0; br <= 15; br++) {
for (uint32_t dr = 0; dr < 2; dr++) {
ref = (PCLK * (1U + dr) / baudrate_prescaler[i]) / baudrate_scaler[br];
if (ref > (uint32_t)hz)
continue;
f_error = hz - ref;
if (f_error < p_error) {
ref_spr = br;
ref_prescaler = i;
ref_dr = dr;
p_error = f_error;
}
}
}
}
// set PBR and BR
obj->spi->CTAR[0] &= ~(SPI_CTAR_PBR_MASK | SPI_CTAR_BR_MASK | SPI_CTAR_DBR_MASK);
obj->spi->CTAR[0] |= (ref_prescaler << SPI_CTAR_PBR_SHIFT) | (ref_spr << SPI_CTAR_BR_SHIFT) | (ref_dr << SPI_CTAR_DBR_SHIFT);
}
/******************************************************************************
* Timer for us timing.
******************************************************************************/
static void pit_init(void) {
SIM->SCGC6 |= SIM_SCGC6_PIT_MASK; // Clock PIT
PIT->MCR = 0; // Enable PIT
pit_ldval = bus_frequency() / 1000000;
PIT->CHANNEL[0].LDVAL = pit_ldval; // 1us
PIT->CHANNEL[0].TCTRL |= PIT_TCTRL_TIE_MASK;
PIT->CHANNEL[0].TCTRL |= PIT_TCTRL_TEN_MASK; // Start timer 1
NVIC_SetVector(PIT0_IRQn, (uint32_t)pit0_isr);
NVIC_EnableIRQ(PIT0_IRQn);
}
/******************************************************************************
* Timer for us timing.
******************************************************************************/
static void pit_init(void) {
SIM->SCGC6 |= SIM_SCGC6_PIT_MASK; // Clock PIT
PIT->MCR = 0; // Enable PIT
// Channel 1
PIT->CHANNEL[1].LDVAL = 0xFFFFFFFF;
PIT->CHANNEL[1].TCTRL = PIT_TCTRL_CHN_MASK; // Chain to timer 0, disable Interrupts
PIT->CHANNEL[1].TCTRL |= PIT_TCTRL_TEN_MASK; // Start timer 1
// Use channel 0 as a prescaler for channel 1
PIT->CHANNEL[0].LDVAL = (bus_frequency() + 500000) / 1000000 - 1;
PIT->CHANNEL[0].TCTRL = PIT_TCTRL_TEN_MASK; // Start timer 0, disable interrupts
}
void us_ticker_init(void) {
if (us_ticker_inited)
return;
us_ticker_inited = 1;
SIM->SCGC6 |= SIM_SCGC6_PIT_MASK; // Clock PIT
PIT->MCR = 0; // Enable PIT
clk_mhz = bus_frequency() / 1000000;
timer_init();
ticker_init();
}
