readme: upgrade readme with logger instruction

README

@@ -34,6 +34,83 @@ xtensa-byt-elf-objcopy -I binary -O elf32-xtensa-le -B xtensa image.bin image.bi
 
 xtensa-byt-elf-objdump -D image.bin.elf > image.dis.txt
 
+
+sof-logger
+======
+
+sof-logger is used to print logs delivered from FW dma_trace mechanism, by searching log
+entries in *.ldc file generated by rimage. 
+
+Every entry declared in FW is placed in elf output file (e.g. sof-apl) in 
+.static_log_entries section in a form of struct defined in sof/src/include/sof/trace.h
+in sof fw repo.
+
+*.ldc file contains snd_sof_logs_header (defined in rmbox/logger_convert.c) 
+following by .static_log_entries section incorporated from FW elf file (e.g. sof-apl).
+snd_sof_logs_header contains basic information about .static_log_entries section
+like base_address and data_length.
+
+sof-logger works by reading entry parameters value and entries addresses from FW
+dma_trace mechanism and searching suitable entry in *.ldc file by its address.
+
+Usage sof-logger <option(s)> <file(s)>
+			Display mailbox contents
+-h			help
+-l *.ldc_file		Specify the *.ldc file
+-i in_file		Get traces from in_file, instead of the default 
+			"/sys/kernel/debug/sof/etrace"
+-o out_file		Specify the output file, instead of default stdout
+-t			Get traces from "/sys/kernel/debug/sof/trace", instead 
+			of the default "/sys/kernel/debug/sof/etrace"
+-p			Get traces from stdin, instead of the default 
+			"/sys/kernel/debug/sof/etrace"
+-c			Set timestamp clock in MHz
+-s			Take a snapshot of state
+
+
+Examples:
+
+- Get traces from "/sys/kernel/debug/sof/etrace" file and prints logs to stdout
+
+  $ sof-logger -l ldc_file
+
+- Get traces from "/sys/kernel/debug/sof/etrace" file and prints logs to
+  out_file file
+
+  $ sof-logger -l ldc_file -o out_file
+
+- Get traces from "/sys/kernel/debug/sof/trace" file and prints logs to stdout
+
+  $ sof-logger -l ldc_file -t
+
+- Get traces from "/sys/kernel/debug/sof/trace" file and prints logs to 
+  out_file file
+
+  $ sof-logger -l ldc_file -t -o out_file
+
+- Get traces from stdin and prints logs to stdout
+
+  $ sof-logger -l ldc_file -p
+
+- Get traces from stdin and prints logs to out_file file
+
+  $ sof-logger -l ldc_file -p -o out_file
+
+- Get traces from trace_dump file and prints logs to stdout
+
+  $ sof-logger -l ldc_file -i trace_dump
+
+- Get traces from trace_dump file and prints logs to out_file file
+
+  $ sof-logger -l ldc_file -i trace_dump -o out_file
+
+- c flag is intented for defining clock value (in MHz) used to format log 
+  timestamps. By default clock value is set to 19.2 (MHz). Below example
+  set clock value to 19.9 (MHz).
+
+  $ sof-logger -l ldc_file -i trace_dump -o out_file -c 19.9
+
+
 tests
 =====