Update! I've solved my own problem and thought I'd share for any lost soul in the future who seeks these answers.
If you look at the technical reference manual for the am355x section 26-3 it shows an interrupt vector table which exists wildly far away from your application entrypoint. Upon closer inspection, I realized some entries are listed twice. This is because the interrupt vector table is actually a bunch of indirection. If you want to set the IRQ branch *address* you specify the address at location 0x4030_CE38 If you want to set the pre-fetch abort *address* you specify the address at location 0x4030_CE2C Example code: // Set the IRQ handler to the entrypoint of the application + 24 bytes *(0x4030_CE38 as *mut u32) = 0x402F_0400 + 0x18; I assumed I needed to write an actual branch *instruction* to those locations. Which is where my confusion started. So if you are building a low-level kernel and are working with interrupts, just remember that the vector table can be updated by simply writing the correct *address* to your handler based on the vector table in the reference manual (*not *an actual branch instruction). On Friday, March 5, 2021 at 6:12:00 AM UTC-8 Josh Cole wrote: > Hi everyone, > > I'm working on a low-level kernel for the Beaglebone Black. I've gotten to > a point in my project where I want to specify an IRQ handler and enable > interrupts. > > According to the technical reference manual > <http://www.sal.wisc.edu/st5000/datasheets/tq-systems/spruh73p.pdf>(section > 26.1.4), there are two primary locations you can load a disk image to. The > first is what they call "Public ROM" which seems pretty straightforward. > You load your image to address 0x20000 and the interrupt vector table is > the first thing which gets encountered. > > The second location you can load an image is "Public RAM" (which I'm > using). This starts executing at 0x402F0400 and you get 109kb of space for > your application. The weird part is, *the interrupt vector table > appears to be located super far away from the entrypoint*, at location > 0x4030CE00. This is more than 109kb away, so it can't be included in the > image which gets flashed to the device. > > I am at a loss about how to get an instruction to that particular location > in memory since my image fundamentally can't be that size. Any guidance on > how to setup the IVT for Public RAM would be greatly appreciated. > > Thank you for your time! > -- 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 beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/b63bc711-fcda-497b-b4e5-ee35c0081176n%40googlegroups.com.
