Reading 64-bit timer

[toptensoftware]

Hi, I stumbled across your docs here while searching for info on reading the 64-bit system timer on raspberry pi and noted your comment about not being able to reliably read the two 32-bit parts atomically:

raspberry-pi/doc/Part 06 Reading the system timer with C++ on a Raspberry Pi.md

Line 15 in 2d17d2f

(which Raspbian is) there is no guarantee that we could read the high 32 bit

You might be interested in this document, where in the section on "64-bit timer read/write" it mentions that if you read the LS32 first, the MS32 is gated to allow accurate reading of the 64-bit value:

https://datasheets.raspberrypi.com/bcm2836/bcm2836-peripherals.pdf

When reading the 64-bit timer value the user must always read the LS 32 bits first. At the same time the
LS-32 bits are read, internal a copy is made of the MS-32 bits into a timer-read-hold register. When
reading the timer MS-32 bits actually the timer-read-hold register is read