AM335x Exception during indirect register access

Ingo Maass

Hi,

first of all I am sorry if this post is incomplete. I can not imagine what the fellow readers here might need to answer my question but I am sure they will tell me. So here it is:

I run a function to read a timer which is called every few microseconds and most of the time works just fine. However, sometimes I get a prefetch abort exception with either

IFSR=0x00000005, IFAR=0x00000004 and Link=0x00000008

IFSR=0x0000000d, IFAR=0x49000000 and Link=0x49000004

Using ETB I get the following result (shortened)

Disassembly

Program Address

Code

Read Address

Write Address

Cycle

Delta Cycles

LDR R1, 0x800381A4	0x8003808C	0x4945			2015	1
			0x800381A4		2016	5
LDR R0, [SP]	0x8003808E	0x9800			2021	1
			0x80E030B8		2022	5
STR R0, [R1]	0x80038090	0x6008			2027	1
				0x803C1D00	2028	5
LDR R1, 0x800381A8	0x80038092	0x4945			2033	1
			0x800381A8		2034	5
LDR R0, [SP, #0x8]	0x80038094	0x9802			2039	1
			0x80E030C0		2040	5
LDR R2, [R1]	0x80038096	0x680A			2045	1
			0x40810204		2046	7
ADD R0, R0, R2	0x80038098	0x1880			2053	1
STR R0, [R1]	0x8003809A	0x6008			2054	1
LDR R0, 0x800381A8	0x8003809C	0x4842			2055	1
LDR R0, [R0]	0x8003809E	0x6800			2056	1
POP {R1, R2, R3, PC}	0x800380A0	0xBD0E			2057	1

Note that "Delta Cycles" says 7 while the same sequence usually looks like this (Delta Cycles = 5):

LDR R1, 0x800381A8	0x80038092	0x4945			1812	1
			0x800381A8		1813	5
LDR R0, [SP, #0x8]	0x80038094	0x9802			1818	1
			0x80E030C0		1819	5
LDR R2, [R1]	0x80038096	0x680A			1824	1
			0x803C1D04		1825	5
ADD R0, R0, R2	0x80038098	0x1880			1830	0
STR R0, [R1]	0x8003809A	0x6008			1830	1
				0x803C1D04	1831	2
LDR R0, 0x800381A8	0x8003809C	0x4842			1833	1
			0x800381A8		1834	5
LDR R0, [R0]	0x8003809E	0x6800			1839	1
			0x803C1D04		1840	5
POP {R1, R2, R3, PC}	0x800380A0	0xBD0E			1845	1
			0x80E030B8		1846	5
			0x80E030BC		1851	1
			0x80E030C0		1852	1
			0x80E030C4		1853	4