Part Number: AM3359
Other Parts Discussed in Thread: ADS8688
Tool/software: TI-RTOS
Hi TI,
beaglebone black, processor SDK RTOS 4.2.0.9, ccs 7.4
I ported PRU-SPI to TI-RTOS from ///github.com/.../
However, my PRU-SPI runs quite slow, only about 1Mbps.
I have added the following function to pru_spi.c. Note __delay_cycles(DELAY_CNT) helps to settle down the bit-transfer.
#define DELAY_CNT 20
uint8_t pru_spi_writertestonly(volatile uint32_t *pTxbuf, volatile int tx_cnt)
{
// write bit to __R30
int i, j;
uint8_t data_byte;
// Set MOSI high
__R30 = __R30 | (1 << MOSI); // Turn on data bit
// First assert CS down
__R30 = __R30 & ~(1 << CS);
// set clk down
__R30 = __R30 & ~(1 << CLK); // Turn off clk
// ----> Clock out Tx command from MOSI
// Loop over data words *pTxbuf
for (i=0; i<tx_cnt; i++) {
data_byte = (uint8_t) *(pTxbuf+i);
// Loop over bits in byte
for (j=0; j<8; j++) {
// set clk down
__R30 = __R30 & ~(1 << CLK); // Turn off clk
// Now set bit
if ( (data_byte<<j) & 0x80 ) { // 1 bit
__R30 = __R30 | (1 << MOSI); // Turn on data bit
} else { // 0 bit
__R30 = __R30 & ~(1 << MOSI); // Turn off data bit
}
// Delay to let bit settle
__delay_cycles(DELAY_CNT);
} // loop over bits
// Quick delay before next byte
__delay_cycles(DELAY_CNT);
} // loop over bytes
// Set MOSI low while clocking in reply
__R30 = __R30 & ~(1 << MOSI); // Transmit 0 bit
// Bring CS back up at end of transaction
__R30 = __R30 | (1 << CS);
return 0x00;
}
I have 3 questions to ask,
1. what's the speed limitation of PRU-SPI on am335x?
2. how can I setup bit transfer speed in a systematic way, rather than change __delay_cycles(DELAY_CNT) ?
3. does TI have example projects or any other suggestions for PRU-SPI than the above approach?
Please advise, thanks in advance
Mike
