K20 EVM - Kinetis Cortex-M4 SPI 테스트
Cortex-M4 K20 SPI 관련 자료 정리.
SPI클럭은 최대 25로 동작한다.
K20 SPI블록도
K20 SPI 제어 레지스터
MKL25Z 보다 기능이 많아서 레지스터가 많이 복잡해 졌다. 하지만 SPIx_MCR, SPIxCTA 레지스터만 보면 대부분의 기본 기능을 사용할 수 있다. 물론 다양한 설정으로 좀더 복잡한 기능을 구현 가능하다.
11 CLR_TXF
Clear TX FIFO
Flushes the TX FIFO. Writing a 1 to CLR_TXF clears the TX FIFO Counter. The CLR_TXF bit is always
read as zero.
0 Do not clear the TX FIFO counter.
1 Clear the TX FIFO counter.
10 CLR_RXF
Flushes the RX FIFO. Writing a 1 to CLR_RXF clears the RX Counter. The CLR_RXF bit is always read
as zero.
0 Do not clear the RX FIFO counter.
1 Clear the RX FIFO counter.
9-8 SMPL_PT
Sample Point
Controls when the DSPI master samples SIN in Modified Transfer Format. This field is valid only when
CPHA bit in CTARn[CPHA] is 0.
00 0 system clocks between SCK edge and SIN sample
01 1 system clock between SCK edge and SIN sample
10 2 system clocks between SCK edge and SIN sample
11 Reserved
K20 SPI 초기화 함수
void SPI0_Init(void)
{
SIM_SCGC5 |= SIM_SCGC5_PORTC_MASK; //Turn on clock to D module
SIM_SCGC6 |= SIM_SCGC6_SPI0_MASK;
//_SPI0_IO_INIT();
PORTC_PCR5=PORT_PCR_MUX(2);//PC5，SPI0 SCK
PORTC_PCR6=PORT_PCR_MUX(2);//PC6，SPI0 SOUT
PORTC_PCR7=PORT_PCR_MUX(2);//PC7，SPI0 SIN
//SPI_C1_CPOL_MASK
//SPI_C1_CPHA_MASK
Sbi(SPI0_MCR, SPI_MCR_HALT_MASK|SPI_MCR_MSTR_MASK);
Sbi(SPI0_MCR, SPI_MCR_DCONF(0x0));
Cbi(SPI0_MCR, SPI_MCR_MDIS_MASK);
Sbi(SPI0_MCR, SPI_MCR_CLR_TXF_MASK | SPI_MCR_CLR_RXF_MASK);
SPI0_TCR = SPI_TCR_SPI_TCNT(0x00);
Cbi(SPI0_CTAR0, SPI_CTAR_DBR_MASK);
SPI0_CTAR0 = SPI_CTAR_FMSZ(7); //8bit
SPI0_SetSpeed(SPI_SPEED_4MHZ);
//SPI Mode
//Sbi(SPI0_CTAR0, SPI_CTAR_CPHA_MASK);
//Sbi(SPI0_CTAR0, SPI_CTAR_CPOL_MASK);
//SPI0_MCR: HALT=0
Cbi(SPI0_MCR, SPI_MCR_HALT_MASK);
}
SPIxCTA 레지스터
17-16 PBR
Baud Rate Prescaler
Selects the prescaler value for the baud rate. This field is used only in Master mode. The baud rate is the
frequency of the SCK. The system clock is divided by the prescaler value before the baud rate selection
takes place. See the BR field description for details on how to compute the baud rate.
00 Baud Rate Prescaler value is 2.
01 Baud Rate Prescaler value is 3.
10 Baud Rate Prescaler value is 5.
11 Baud Rate Prescaler value is 7.
3-0 BR
Baud Rate Scaler
Selects the scaler value for the baud rate. This field is used only in Master mode. The prescaled system
clock is divided by the Baud Rate Scaler to generate the frequency of the SCK. The baud rate is
computed according to the following equation:
SCK baud rate = (fSYS/PBR) x [(1+DBR)/BR]
K20 SPI 송수신 함수
unsigned char SPI0_WriteReadByte(unsigned char Data)
{
//SPTEF - 1 이면 데이터 전송
unsigned char temp;
while (!(SPI0_SR & SPI_SR_TFFF_MASK)) ;
//Write char to SPI
SPI0_PUSHR = Data;
//SPRF - 1 이면 데이터 수신
//while (!(SPI0_SR & SPI_SR_RXCTR_MASK)) ;
while (!(SPI0_SR & SPI_SR_RFDF_MASK)) ;
temp = SPI0_POPR;
SPI0_SR = SPI_SR_TFFF_MASK | (SPI0_SR&SPI_SR_RFDF_MASK);
return temp;
}
K20 SPI SPIxTCR 레지스터
좀 특이한 사항으로 하드웨어적으로 TCR레지스터가 있어 전송 회수를 알 수 있고 이를 이용해서 버퍼 관리가 편리해 진다. 이부분은 좀더 들여다 볼 필요가 있는것 같다.
K20 SPI모드 설정
