I recently received a copy of 
"Raspberry Pi IoT in C" by Harry Fairhead, 3rd Edition published by I/O Press. 
ISBN 9781871962840
https://www.amazon.com/Raspberry-Pi-IoT-C-3rd/dp/1871962846
This is an excellent introduction to setting up and using this bcm2835 
library, with many examples and  extremely good illustrations. Recommended for 
beginner and intermediate level programmers,  though some advanced topics like 
interrupts and scheduling are also covered.
-- 
Mike McCauley           VK4AMM                   
mi...@airspayce.com
Airspayce Pty Ltd 9 Bulbul Place Currumbin Waters QLD 4223 Australia   
http://www.airspayce.com                                 5R3MRFM2+X6
Phone 
+61 7 5598-7474