On Tue, Aug 22, 2017 at 11:51 AM, [email protected] <[email protected]> wrote: > Long story short I have a custom board for personal use that is essentially > a cape for the BBB. It has a 24c256 EEPROM on I2C-2, just like the example > in the reference manual. > > I'm having severe difficulty interpreting these lines though: >> >> Address line A2 is always tied high. This sets the allowable address range >> for the expansion cards to 0x54 to 0x57. All other I2C addresses can be used >> by the user in the design of their capes. > > > When I boot the BBB and run i2cdetect on i2c-2, I can see that addresses > 0x54-0x57 are reserved by the kernel, because they're shown as "UU" in the > i2cdetect output. This means I can't read/write to this chip if I want to, > as I don't have permission from userland. > > So from what I can tell with all of this, and please correct me if I'm being > an idiot, is that you want to use addresses 0x54-0x57 to store read only > pinmux data for your cape, and the kernel can pick this up and adapt > according via device trees or whatever. If you want a readable/writeable > EEPROM for other information you would have to tie A2 to ground, and thus > move the address out of the kernel reserved space, making it something > between 0x50-0x53. Is this correct, or am I just horrible misinterpreting > the reference manual? > > Any pointers would be great at this point, I just want to make sure I really > understand the reason those addresses are reserved by the kernel, and what > an eeprom with those addresses is actually used for. Thanks.
They are used by the kernel's cape-manager.. If you want to use that address, and you have an eeprom. Just ignore the i2cdetect output, and just access the eeprom thru /sys/bus/i2c/devices/2-0054/eeprom /sys/bus/i2c/devices/2-0055/eeprom /sys/bus/i2c/devices/2-0056/eeprom /sys/bus/i2c/devices/2-0057/eeprom Regards, -- Robert Nelson https://rcn-ee.com/ -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAOCHtYjT8TDrY9kzyAi1q06fNW%3DYV%3Dh_Zht%2BV2SAiFV_VXDXWQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
