Hello,
I noticed a delay between the bytes/words (about 4µs) while sending SPI frames as illustrated here:
I couldn’t figure out the reason of it. Is it not possible to send the bytes continuously without pausing the SCLK between the bytes? is this behaviour because of the SPI driver? if yes could you suggest a SPI transfer function/driver.
Used functions:
#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
static const char *device = "/dev/spidev2.0";
uint8_t tx[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0x40, 0x00, 0x00, 0x00, 0x00, 0x95,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
0xF0, 0x0D,
};
uint8_t default_rx[ARRAY_SIZE(tx)];
void SPI_init()
{
speed =1000000; //10Mhz
bits = 8;
fd = open(device, O_RDWR);
if (fd < 0)
pabort("can't open device");
// spi mode
ret = ioctl(fd, SPI_IOC_WR_MODE32, &mode);
if (ret == -1)
pabort("can't set spi mode");
ret = ioctl(fd, SPI_IOC_RD_MODE32, &mode);
if (ret == -1)
pabort("can't get spi mode");
//bits per word
ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
if (ret == -1)
pabort("can't set bits per word");
ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
if (ret == -1)
pabort("can't get bits per word");
// max speed hz
ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
if (ret == -1)
pabort("can't set max speed hz");
ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
if (ret == -1)
pabort("can't get max speed hz");
}
static void SPI_transfer(int fd, uint8_t const *tx, uint8_t const *rx, size_t len)
{
int ret;
struct spi_ioc_transfer tr = {
.tx_buf = (unsigned long)tx,
.rx_buf = (unsigned long)rx,
.len = len,
.delay_usecs = delay,
.speed_hz = speed,
.bits_per_word = bits,
};
ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
if (ret < 1)
pabort("can't send spi message");
}
int main ()
{
SPI_init();
SPI_transfer(fd, tx, rx, ARRAY_SIZE(tx));
}
Device Tree:
&ecspi3 {
status = "okay";
mcp258x0: mcp258x@0 {
compatible = "microchip,mcp2515";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_can_int>;
reg = <0>;
clocks = <&clk16m>;
interrupt-parent = <&gpio5>;
interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
spi-max-frequency = <10000000>;
status = "disabled";
};
spidev0: spidev@0 {
compatible = "toradex,evalspi";
reg = <0>;
spi-max-frequency = <23000000>;
status = "okay";
};
};
Thanks in advance.
Best regards,
Majd