I'm not familiar with the McSPI hardware module, but this seems to explain a good bit. And seems analogous( similar ) to how one would enable the ADC module - Which is the only module I have hands on experience with by poking it's registers . . e.g. turning the clock on, etc.
https://github.com/BeaglePilot/PRUSS-C/blob/master/PRUSS_LIB/AM335X_StarterWare_02_00_01_01/drivers/mcspi.c#L378-L469 On Thu, Dec 17, 2015 at 4:48 PM, William Hermans <[email protected]> wrote: > I've no idea how ioremap() works, never used it. But if it's similar to > how mmap() works on /dev/mem/, it does not matter what state the hardware > module is in. Of course there are a few specified steps one must do in > order to get a device working if it's not already. But if the device is > already on, and functional, you can essentially override that module with > mmap() and /dev/mem/. But it's probably not good idea, as the kernel will > still think it has control . . . > > Anyway, I'm not sure I'd exactly call this a "driver" per se, as it's > being done in userspace. But others might argue it's what's called a > userspace driver . . . and yeah, I do not know about that. If you start > changing pixels on your screen by poking at memory locations through > /dev/mem/ does that mean you've created a graphics driver ? No . . . > > On Thu, Dec 17, 2015 at 4:08 PM, John Syne <[email protected]> wrote: > >> >> On Dec 17, 2015, at 3:00 PM, William Hermans <[email protected]> wrote: >> >> *That is a good point. To understand how to enable the power and clock >>> for McASP, look at the Starterware examples for McASP as they do everything >>> you need to make this work.* >>> >> >> Probably easier, and more productive to read the TRM for the AM335x >> processors . . . All address offsets should be listed there as well, and >> the introduction for hardware module will give a short explanation of what >> needs doing, in order to bring the module up. >> >> Yeah, thinking about what Charles said, if he defines the McASP in the >> device tree, it should setup everything he needs. One problem I’m not sure >> how to overcome, he needs a device driver defined for the McASP or else the >> clock and power won’t be setup. But if he has a device driver setup, then >> it will conflict with his application. So that is why I think he has to do >> all this manually. >> >> Regards, >> John >> >> >> On Thu, Dec 17, 2015 at 3:15 PM, John Syne <[email protected]> wrote: >> >>> >>> >>> > On Dec 17, 2015, at 1:59 PM, Charles Steinkuehler < >>> [email protected]> wrote: >>> > >>> > On 12/17/2015 2:04 PM, [email protected] wrote: >>> >> I am trying to access the McASP control registers. Reading from the >>> first >>> >> one fails with the kernel oops stating "external abort on >>> non-linefetch >>> >> (0x1028)". I dont know what that means. A minimum failing example of >>> the >>> >> code is below: >>> > >>> > <snip> >>> > >>> >> I have also tried request_mem_region around it, but that changes >>> nothing. >>> >> The sound drivers are not loaded, and the devicetree entry for the >>> McASP is >>> >> disabled, so there shouldn't be any problems with conflicts. >>> > >>> > One way to get this error is if the hardware you are talking to is >>> > disabled. You need to either enable the hardware via the device tree, >>> > or otherwise manage to setup the low-level SoC registers so the McASP >>> > is provided a clock, power, and is taken out of reset. >>> > >>> > Most of the hardware blocks on the AM335x series can be individually >>> > enabled or shut-down to save power. >>> That is a good point. To understand how to enable the power and clock >>> for McASP, look at the Starterware examples for McASP as they do everything >>> you need to make this work. >>> >>> Regards, >>> John >>> > >>> > -- >>> > Charles Steinkuehler >>> > [email protected] >>> > >>> > -- >>> > 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]. >>> > For more options, visit https://groups.google.com/d/optout. >>> >>> -- >>> 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]. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> -- >> 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]. >> For more options, visit https://groups.google.com/d/optout. >> >> >> -- >> 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]. >> For more options, visit https://groups.google.com/d/optout. >> > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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