The starting point for my questions is the BB-SPIDEV0-00A0.dts.
1. Description of problem:
The following fragment was taken from the above device tree spec:
fragment@0 {
target = <&am33xx_pinmux>;
__overlay__ {
/* default state has all gpios released and mode set to uart1 */
bb_spi0_pins: pinmux_bb_spi0_pins {
pinctrl-single,pins = <
0x150 0x30 /* spi0_sclk.spi0_sclk, INPUT_PULLUP | MODE0 */
0x154 0x30 /* spi0_d0.spi0_d0, INPUT_PULLUP | MODE0 */
0x158 0x10 /* spi0_d1.spi0_d1, OUTPUT_PULLUP | MODE0 */
0x15c 0x10 /* spi0_cs0.spi0_cs0, OUTPUT_PULLUP | MODE0 */
>;
};
};
};
The fragment configures the P9.17, P9.18, P9.21, P9.22 pins to Mode 0 for the SPI driver. I’m also aware of the table P9 Header table with the offset addresses of the pins and the AM335x Sitara Processors Technical Reference Manual (Rev. M) with information on how to configure the CPU registers.
My problem is that the addresses in the device tree fragment above do not match the addresses in the Reference Manual.
In the fragment above the offset addresses are: 0x150, 0x154, 0x158 and 0x15c. In the Reference Manual Chapter 9.3 page 1372 the offset addresses are: 0x950, 0x954, 0x958, 0x95c.
Question: Can someone help me understand where are the addresses from the fragment taken/obtained/calculated from?
2. Description of problem
The following fragments were taken from the above device tree specification:
...
fragment@0 {
target = <&am33xx_pinmux>;
__overlay__ {
...
...
fragment@1 {
target = <&spi0>; /* spi0 is numbered correctly */
__overlay__ {
...
I could not find on the web what is the functionality of the target property in a device tree. I’m somehow familiar with the aliases concept. So I think &am33xx_pinmux and &spi0 are aliases for “something”. However there is nothing defined in the device tree specification above.
Questions:
What is the functionality/role of the target property? Where are the &am33xx_pinmux and &spi0 defined and what do they mean?
I would also appreciate some links/references if available, so I can further read.
I’m also interested if there is a list with all the aliases for BeagleBone Black.