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by gpk
Tue Apr 09, 2019 8:45 pm
Forum: Bare metal, Assembly language
Topic: CPU Execution Speed
Replies: 10
Views: 1407

Re: CPU Execution Speed

I have also noticed this. I thought (probably naively) that following routine would cause a busy wait for roughly n cycles: wait_cycles: cmp x0, 0 ble end sub x0, x0, #4 // we'll spend 4 cycles in the loop b wait_cycles end: ret But it actually waits for about 30x more cycles than I thought it would...
by gpk
Sat Apr 06, 2019 10:49 am
Forum: Bare metal, Assembly language
Topic: Yet Another Bare Metal Tutorial for the RPi3
Replies: 77
Views: 51464

Re: Yet Another Bare Metal Tutorial for the RPi3

Another book that is very good is "Operating System Design, The Xinu Approach" by Douglas Comer. It cover the implementation of a small embedded OS called Xinu. Xinu also runs on Raspberry Pi, there is a port here: https://github.com/LdB-ECM/Xinu (note I had to do some changes to get it to build, th...
by gpk
Mon Mar 25, 2019 9:12 pm
Forum: Bare metal, Assembly language
Topic: Yet Another Bare Metal Tutorial for the RPi3
Replies: 77
Views: 51464

Re: Yet Another Bare Metal Tutorial for the RPi3

Why does this code use 0x3f215000 as the AUX peripherals map when the BCM2835 documentation says its 0x7e215000? I noticed that Linux uses the latter while this code (and others) use the former.

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