Deep Dive w/Scott: ARMv8A MMU

Join Scott as he continues his quest to get TinyUSB running on the Raspberry Pi 4 and answers questions folks have. Support Adafruit, and by extension me, by purchasing hardware from https://adafruit.com Chat with me and lot of others on the Adafruit Discord at https://adafru.it/discord. No stream next week! Latest code is here: https://github.com/tannewt/tinyusb/tree/rpi 0:00 Getting started 0:01:30 audio debrief from last week 0:03:28 housekeeping 0:08:00 First time watching your live stream. What are we learning today? 0:09:10 Cortex A / MMU 0:10:20 ​If you learn original python on a pc, is it then easy to go from there to circuit python? 0:11:10 qemu further progress 0:13:40 board init() 0:15:30 unaligned access 0:17:30 What model of Pi will this run on? And will it be ARM32 or 64? 0:19:10 if you run CP on metal RPI4, is there the need for 32 bits? 0:21:15 local setup on desk 0:22:30 OSH Park Pi Development v1 project to eliminate all the wires above 0:25:00 https://github.com/chickadee-tech/pi-developer 0:25:45 catch the exceptions in boot.s 0:27:40 load VBAR_EL1 with virtual vector table address 0:29:00 arm stub switches from EL3? to EL2 0:29:40 4-way split terminal tinyusb, serial, gdb 0:32:22 cortex-a.py (in gdb) 0:32:47 ARM Cortex-A Programmers Guide for ARMv8-A pdf (MMU overview) 0:34:15 TTBR0_EL0 (EL2) 0:35:10 Arm architecture reference DDIO487G_b_armv8_arm.pdf 0:35:51 ESR_EL2 register 0:38:42 cortex-a.py - decode exception code 0:40:15 Python pattern matching in python 3.10 (match switch) 0:41:45 What other information can we extract from the exception 0:42:25 FAR ( fault address register? ) / extend the decoding 0:50:45 ashw.io/blog/arm64-pgtable-tool - and youtube video 0:54:00 decoding virtual address ( from BruceS ) 0:56:20 pi4 address map from bcm2711-peripherals(1).pdf 0:58:00 setup_mmu_flat_map() in mmu.c 1:00:10 Level 1 access flag fault 1:02:00 Translation fault level 1 1:03:30 access flag fault level 1 1:06:20 Long-descriptor level 1 and level 2 descriptor formats 1:10:00 github ashwio/arm64-pgtable-tool python code 1:14:10 “The Access flag” , ok, add the MM_DESCRIPTOR_ACCESS_FLAG 1:17:10 got a little further - maybe try it out on the hardware (instead of qemu) 1:22:30 decode the Data Abort further - translation fault level 1 1:27:50 we have uart output! 1:29:00 summary - flags in translation table needed to get access flag set to 1 1:39:00 dcd_init() 1:39:58 What side projects are you looking forward to diving deeper into in the coming weeks? 1:42:00 Did you ever ask adafruit to manufacture your old board? 1:44:04 UPS truck arrived - (new iPhone? ) Be right back 1:45:58 back - unboxing 1:51:45 recap - MMU / fixed table lookup / added access flag / used python to decode information about access fault / uart output 1:53:00 next steps 1:53:54 wrap up 1:55:50 - see you in two week Visit the Adafruit shop online - http://www.adafruit.com ----------------------------------------- LIVE CHAT IS HERE! http://adafru.it/discord Adafruit on Instagram: https://www.instagram.com/adafruit Subscribe to Adafruit on YouTube: http://adafru.it/subscribe New tutorials on the Adafruit Learning System: http://learn.adafruit.com/ -----------------------------------------