Hi,
-----Original Message----- From: Al Grant Al.Grant@arm.com Sent: Monday, September 2, 2019 3:29 PM To: Linu Cherian lcherian@marvell.com; coresight@lists.linaro.org Cc: Sunil Kovvuri Goutham sgoutham@marvell.com Subject: [EXT] RE: Tracing and decoding support for trace hardware without trace formatter
- Does openCSD tool supports decoding of trace capture from hardware
that
has trace formatter disabled.
From the openCSD RRADME, "The library will decode formatted trace in three stages:
Frame Deformatting : Removal CoreSight frame formatting from individual
trace
streams. Packet Processing : Separate individual trace streams into discrete
packets.
Packet Decode : Convert the packets into fully decoded trace describing
the
program flow on a core."
So, is it possible for openCSD to carry out decoding bypassing the first
stage
mentioned above.
Yes,
https://github.com/Linaro/OpenCSD/blob/master/decoder/docs/prog_gui de/prog_guide_main.md
says
"In limited cases where the hardware has a single trace source, or only a single source is being used, then it is possible to switch off the hardware frame formatter in the ETB/ETR/TPIU. In this case @ref OCSD_TRC_SRC_SINGLE (from enum @ref ocsd_dcd_tree_src_t) may be defined as the first parameter to the function."
But in general, any ETR that can deal with multiple trace sources should support formatting, otherwise the trace will be corrupt if more than one trace source is enabled. Practically the only reason ever to have an ETR that doesn't support formatting is if the ETR is specific to a single trace source (e.g. one ETR per CPU).
Yes. We have one ETR per CPU.
- Linux Coresight ETR driver as part of managing the trace buffer wrap
condition, a barrier packet is written at the beginning which is essentially a Frame synchronization packet. This gives an impression that that ETR driver is making an assumption that
the
trace formatter is implemented in hardware. Should we not need a fix here, to accommodate hardware configurations
that
doesn't support trace formatter as well ?
That would be sensible. Even if the ETR does support formatting, in some cases (e.g. the case of one ETR per CPU) there may be a slight bandwidth improvement in turning it off.
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