I’ve got a problem with configuration of SPI1 of BeagleBone White using PRU. The SPI works with external ADC in receive only mode
during boot (ubuntu minimal) I do pin mux:
//SPI CLK (output, mode3)
echo 13 > /sys/kernel/debug/omap_mux/mcasp0_aclkx
//D1 (input, pull-up, mode3)
echo 33 > /sys/kernel/debug/omap_mux/mcasp0_axr0
then using PRU I configure SPI:
//enable clock for SPI1
0x44e0_0050 = 0x2
//reset SPI1
0x481a_0110 = 0x2
then I wait till the reset is done
//configure channels
0x481a_012c = 0x7188a (d1 - input, no trans on d0&d1, receive only mode, 18-bit world, ADC SPI polarity)
0x481a_0140 = 0x6188a (not used)
0x481a_0154 = 0x6188a (not used)
0x481a_0168 = 0x6188a (not used)
//module configuration
0x481a_0128 = 0x0
//system configuration (order recommended in datasheet)
0x481a_0110 = 0x15
//enable ch0
0x481a_0134 = 0x1
//write dummy TX data to enable receive only mode
0x481a_0138 = 0x3ffff
then when I read RX register (0x481a_013c) I can see the clock and data on the lines using oscilloscope, but the value of RX register is always 0?