Hello Gary G,
You may download the i.MX8M Quad Reference Manual on the link below (you may need to login to download this file). This document covers the i.MX8M Dual, i.MX8M QuadLite and i.MX8M Quad processors.
https://www.nxp.com/webapp/Download?colCode=IMX8MDQLQRM
Since the HummingBoard is manufactured and supported by SolidRun, if you have specific questions about the HummingBoard hardware or BSP I would need to ask you to please contact SolidRun trough their support channels.
Regards,