Reading Free RAM

Can anyone please tell me how to read the current free RAM from BASIC?

I’ve been using OS_DynamicArea 5, which will only return a maximum of 2GB.
Looking at the wiki, I see this has been superseded by OS_DynamicArea 27.

I can’t get OS_DynamicArea 27 to return anything like the free RAM.
Here is how I’m trying to read it;

SYS”OS_DynamicArea”,27,-1 TO r0%,r1%,r2%
PRINT r0%
PRINT r1%
PRINT r2%

On my Pinebook Pro with 3.6GB RAM free, this prints;
27
-1
888655

Any help would be greatly appreciated!

REM >ReadFree

REM get page size in bytes and number of pages
SYS "OS_ReadMemMapInfo" TO size%,no%
PRINT size%,no%

REM  convert size to KB to keep within 32bit maths
sizek%=size% DIV 1024

SYS "OS_DynamicArea" ,27,-1 TO r0%,r1%,freepages%
PRINT "Number of free pages ";freepages%
PRINT "Free size ";freepages% * sizek%;"KB"
END

sizek%=size% DIV 1024

sizek%=size% >> 10 might be more efficient?

Could also do ((freepages% * sizek%) >> 10) to get the answer in megabytes, which on today’s machines might be an easier number to deal with than kilobytes?

Thanks David & Rick!