OpenCSD - CoreSight Trace Decode Library  0.9.2
prog_guide/prog_guide_generic_pkts.md
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1 OpenCSD Library - Generic Trace Packet Descriptions {#generic_pkts}
2 ===================================================
3 
4 @brief Interpretation of the Generic Trace output packets.
5 
6 Generic Trace Packets - Collection.
7 -----------------------------------
8 
9 ### Packet interface ###
10 
11 The generic trace packets are the fully decoded output from the trace library.
12 
13 These are delivered to the client application in the form of a callback function. Packets from all trace sources
14 will use the same single callback function, with the CoreSight Trace ID provided to identify the source.
15 
16 The callback is in the form of an interface class ITrcGenElemIn, which has a single function:
17 
18 ~~~{.cpp}
19 virtual ocsd_datapath_resp_t TraceElemIn( const ocsd_trc_index_t index_sop,
20  const uint8_t trc_chan_id,
21  const OcsdTraceElement &elem
22  ) = 0;
23 ~~~
24 
25 The client program will create derived class providing this interface to collect trace packets from the library.
26 
27 The parameters describe the output packet and source channel:
28 |Parameter | Description |
29 |:--------------------------------|:------------------------------------------------------------------------|
30 | `ocsd_trc_index_t index_sop` | Index of the first byte of the trace packet that generated this output. |
31 | `uint8_t trc_chan_id` | The source CoreSight Trace ID. |
32 | `OcsdTraceElement &elem` | The packet class - wraps the `ocsd_generic_trace_elem` structure. |
33 
34 _Note_ : `index_sop` may be the same for multiple output packets. This is due to an one byte atom packet which
35 can represent multiple atoms and hence multiple ranges.
36 
37 The C-API provides a similarly specified callback function definition, with an additional opaque `void *` pointer
38 that the client application may use.
39 
40 ~~~{.c}
41 /** function pointer type for decoder outputs. all protocols, generic data element input */
42 typedef ocsd_datapath_resp_t (* FnTraceElemIn)( const void *p_context,
43  const ocsd_trc_index_t index_sop,
44  const uint8_t trc_chan_id,
45  const ocsd_generic_trace_elem *elem);
46 ~~~
47 
48 ### The Packet Structure ###
49 
50 ~~~{.c}
51 typedef struct _ocsd_generic_trace_elem {
52  ocsd_gen_trc_elem_t elem_type; /* Element type - remaining data interpreted according to this value */
53  ocsd_isa isa; /* instruction set for executed instructions */
54  ocsd_vaddr_t st_addr; /* start address for instruction execution range / inaccessible code address / data address */
55  ocsd_vaddr_t en_addr; /* end address (exclusive) for instruction execution range. */
56  ocsd_pe_context context; /* PE Context */
57  uint64_t timestamp; /* timestamp value for TS element type */
58  uint32_t cycle_count; /* cycle count for explicit cycle count element, or count for element with associated cycle count */
59  ocsd_instr_type last_i_type; /* Last instruction type if instruction execution range */
60  ocsd_instr_subtype last_i_subtype; /* sub type for last instruction in range */
61 
62  //! per element flags
63  union {
64  struct {
65  uint32_t last_instr_exec:1; /* 1 if last instruction in range was executed; */
66  uint32_t last_instr_sz:3; /* size of last instruction in bytes (2/4) */
67  uint32_t has_cc:1; /* 1 if this packet has a valid cycle count included (e.g. cycle count included as part of instruction range packet, always 1 for pure cycle count packet.*/
68  uint32_t cpu_freq_change:1; /* 1 if this packet indicates a change in CPU frequency */
69  uint32_t excep_ret_addr:1; /* 1 if en_addr is the preferred exception return address on exception packet type */
70  uint32_t excep_data_marker:1; /* 1 if the exception entry packet is a data push marker only, with no address information (used typically in v7M trace for marking data pushed onto stack) */
71  uint32_t extended_data:1; /* 1 if the packet extended data pointer is valid. Allows packet extensions for custom decoders, or additional data payloads for data trace. */
72  uint32_t has_ts:1; /* 1 if the packet has an associated timestamp - e.g. SW/STM trace TS+Payload as a single packet */
73  };
74  uint32_t flag_bits;
75  };
76 
77  //! packet specific payloads
78  union {
79  uint32_t exception_number; /* exception number for exception type packets */
80  trace_event_t trace_event; /* Trace event - trigger etc */
81  trace_on_reason_t trace_on_reason; /* reason for the trace on packet */
82  ocsd_swt_info_t sw_trace_info; /* software trace packet info */
83  uint32_t num_instr_range; /* number of instructions covered by range packet (for T32 this cannot be calculated from en-st/i_size) */
84 
85  };
86 
87  const void *ptr_extended_data; /* pointer to extended data buffer (data trace, sw trace payload) / custom structure */
88 
89 } ocsd_generic_trace_elem;
90 ~~~
91 
92 The packet structure contains multiple fields and flag bits. The validity of any of these fields or flags
93 is dependent on the `elem_type` member. The client program must not assume that field values will persist
94 between packets, and must process all valid data during the callback function.
95 
96 The packet reference guide below defines the fields valid for each packet type.
97 
98 --------------------------------------------------------------------------------------------------
99 
100 Generic Trace Packets - Packet Reference.
101 -----------------------------------------
102 
103 This section contains reference descriptions of each of the generic trace packets types define as part of the
104 `ocsd_gen_trc_elem_t` enum value that appears as the first `elem_type` field in the packet structure.
105 
106 The descriptions will include information on which fields in the packets are always valid, optional and any protocol specific information.
107 
108 The tags used in the reference are:-
109 - __packet fields valid__ : fields that are always valid and filled for this packet type.
110 - __packet fields optional__ : fields that _may_ be filled for this packet type.
111  The form `flag -> field` indicates a flag that may be set and the value that is valid if the flag is true
112 - __protocol specific__ : indicates type or fields may be source protocol specific.
113 
114 _Note_: while most of the packets are not protocol specific, there are some protocol differences that mean
115 certain types and fields will differ slightly across protocols. These differences are highlighted in the
116 reference.
117 
118 ### OCSD_GEN_TRC_ELEM_NO_SYNC ###
119 __packet fields valid__: None
120 
121 Element output before the decoder has synchronised with the input stream, or synchronisation is lost.
122 
123 ### OCSD_GEN_TRC_ELEM_INSTR_RANGE ###
124 __packet fields valid__: `isa, st_addr, en_addr, last_i_type, last_i_subtype, last_instr_exec, last_instr_sz, num_instr_range`
125 
126 __packet fields optional__: `has_cc -> cycle_count,`
127 
128 __protocol specific__ : ETMv3, PTM
129 
130 This should be the most common packet output for full trace decode. Represents a range of instructions of
131 a single `isa`, executed by the PE. Instruction byte range is from `st_addr` (inclusive) to `en_addr` (exclusive).
132 The total number of instructions executed for the range is given in `num_instr_range`.
133 
134 Information on the last instruction in the range is provided. `last_i_type` shows if the last instruction
135 was a branch or otherwise - which combined with `last_instr_exec` determines if the branch was taken.
136 The last instruction size in bytes is given, to allow clients to quickly determine the address of the last
137 instruction by subtraction from `en_addr`. This value can be 2 or 4 bytes in the T32 instruction set.
138 
139 __ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates
140 the trace range. In this case `has_cc` will be 1 and `cycle_count` will be valid.
141 
142 
143 ### OCSD_GEN_TRC_ELEM_ADDR_NACC ###
144 __packet fields valid__: `st_addr`
145 
146 Trace decoder found address in trace that cannot be accessed in the mapped memory images.
147 `st_addr` is the address that cannot be found.
148 
149 Decoder will wait for new address to appear in trace before attempting to restart decoding.
150 
151 
152 ### OCSD_GEN_TRC_ELEM_UNKNOWN ###
153 __packet fields valid__: None
154 
155 Decoder saw invalid packet for protocol being processed. Likely incorrect protocol settings, or corrupted
156 trace data.
157 
158 ### OCSD_GEN_TRC_ELEM_TRACE_ON ###
159 __packet fields valid__: trace_on_reason
160 
161 __packet fields optional__: `has_cc -> cycle_count,`
162 
163 __protocol specific__ : ETMv3, PTM
164 
165 Notification that trace has started / is synced after a discontinuity or at start of trace decode.
166 
167 __ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates
168 the trace on indicator. In this case `has_cc` will be 1 and `cycle_count` will be valid.
169 
170 
171 ### OCSD_GEN_TRC_ELEM_EO_TRACE ###
172 __packet fields valid__: None
173 
174 Marker for end of trace data. Sent once for each CoreSight ID channel.
175 
176 ### OCSD_GEN_TRC_ELEM_PE_CONTEXT ###
177 __packet fields valid__: context
178 
179 __packet fields optional__: `has_cc -> cycle_count,`
180 
181 __protocol specific__ : ETMv3, PTM
182 
183 This packet indicates an update to the PE context - which may be the initial context in a trace stream, or a
184 change since the trace started.
185 
186 The context is contained in a `ocsd_pe_context` structure.
187 
188 ~~~{.c}
189 typedef struct _ocsd_pe_context {
190  ocsd_sec_level security_level; /* security state */
191  ocsd_ex_level exception_level; /* exception level */
192  uint32_t context_id; /* context ID */
193  uint32_t vmid; /* VMID */
194  struct {
195  uint32_t bits64:1; /* 1 if 64 bit operation */
196  uint32_t ctxt_id_valid:1; /* 1 if context ID value valid */
197  uint32_t vmid_valid:1; /* 1 if VMID value is valid */
198  uint32_t el_valid:1; /* 1 if EL value is valid (ETMv4 traces current EL, other protocols do not) */
199  };
200 } ocsd_pe_context;
201 ~~~
202 
203 __ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates
204 the PE context. In this case `has_cc` will be 1 and `cycle_count` will be valid.
205 
206 __ETMv3__ : From ETM 3.5 onwards, exception_level can be set to `ocsd_EL2` when tracing through hypervisor code.
207 On all other occasions this will be set to `ocsd_EL_unknown`.
208 
209 
210 ### OCSD_GEN_TRC_ELEM_ADDR_UNKNOWN ###
211 __packet fields optional__: `has_cc -> cycle_count,`
212 
213 __protocol specific__: ETMv3
214 
215 This packet will only be seen when decoding an ETMv3 protocol source. This indicates that the decoder
216 is waiting for a valid address in order to process trace correctly.
217 
218 The packet can have a cycle count associated with it which the client must account for when tracking cycles used.
219 The packet will be sent once when unknown address occurs. Further `OCSD_GEN_TRC_ELEM_CYCLE_COUNT` packets may follow
220  before the decode receives a valid address to continue decode.
221 
222 
223 ### OCSD_GEN_TRC_ELEM_EXCEPTION ###
224 __packet fields valid__: `exception_number`
225 
226 __packet fields optional__: `has_cc -> cycle_count, excep_ret_addr -> en_addr, excep_data_marker`
227 
228 __protocol specific__: ETMv4, ETMv3, PTM
229 
230 All protocols will include the exception number in the packet.
231 
232 __ETMv4__ : This protocol may provide the preferred return address for the exception - this is the address of
233 the instruction that could be executed on exception return. This address appears in `en_addr` if `excep_ret_addr` = 1.
234 
235 __ETMv3__ : This can set the `excep_data_marker` flag. This indicates that the exception packet is a marker
236 to indicate exception entry in a 7M profile core, for the purposes of tracking data. This will __not__ provide
237 an exception number in this case.
238 
239 __PTM__ : Can have an associated cycle count (`has_cc == 1`), and may provide preferred return address in `en_addr`
240 if `excep_ret_addr` = 1.
241 
242 ### OCSD_GEN_TRC_ELEM_EXCEPTION_RET ###
243 __packet fields valid__: None
244 
245 Marker that a preceding branch was an exception return.
246 
247 ### OCSD_GEN_TRC_ELEM_TIMESTAMP ###
248 __packet fields valid__: `timestamp`
249 
250 __packet fields optional__: `has_cc -> cycle_count,`
251 
252 __protocol specific__: ETMv4, PTM
253 
254 The timestamp packet explicitly provides a timestamp value for the trace stream ID in the callback interface.
255 
256 __PTM__ : This can have an associated cycle count (`has_cc == 1`). For this protocol, the cycle count __is__ part
257 of the cumulative cycle count for the trace session.
258 
259 __ETMv4__ : This can have an associated cycle count (`has_cc == 1`). For this protocl, the cycle coun represents
260 the number of cycles between the previous cycle count packet and this timestamp packet, but __is not__ part of
261 the cumulative cycle count for the trace session.
262 
263 
264 ### OCSD_GEN_TRC_ELEM_CYCLE_COUNT ###
265 __packet fields valid__: `has_cc -> cycle_count`
266 
267 Packet contains a cycle count value. A cycle count value represents the number of cycles passed since the
268 last cycle count value seen. The cycle count value may be associated with a specific packet or instruction
269 range preceding the cycle count packet.
270 
271 Cycle count packets may be added together to build a cumulative count for the trace session.
272 
273 ### OCSD_GEN_TRC_ELEM_EVENT ###
274 __packet fields valid__: `trace_event`
275 
276 This is a hardware event injected into the trace by the ETM/PTM hardware resource programming. See the
277 relevent trace hardware reference manuals for the programming of these events.
278 
279 The `trace_event` is a `trace_event_t` structure that can have an event type - and an event number.
280 
281 ~~~{.c}
282 typedef struct _trace_event_t {
283  uint16_t ev_type; /* event type - unknown (0) trigger (1), numbered event (2)*/
284  uint16_t ev_number; /* event number if numbered event type */
285 } trace_event_t;
286 ~~~
287 
288 The event types depend on the trace hardware:-
289 
290 __ETMv4__ : produces numbered events. The event number is a bitfield of up to four events that occurred.
291 Events 0-3 -> bits 0-3. The bitfield allows a single packet to represent multiple different events occurring.
292 
293 _Note_: The ETMv4 specification has further information on timing of events and event packets. Event 0
294 is also considered a trigger event in ETMv4 hardware, but is not explicitly represented as such in the OCSD protocol.
295 
296 __PTM__, __ETMv3__ : produce trigger events. Event number always set to 0.
297 
298 
299 ### OCSD_GEN_TRC_ELEM_SWTRACE ###
300 __packet fields valid__: `sw_trace_info`
301 
302 __packet fields optional__: `has_ts -> timestamp`, ` extended_data -> ptr_extended_data`
303 
304 The Software trace packet always has a filled in `sw_trace_info` field to describe the current master and channel ID,
305 plus the packet type and size of any payload data.
306 
307 SW trace packets that have a payload will use the extended_data flag and pointer to deliver this data.
308 
309 SW trace packets that include timestamp information will us the `has_ts` flag and fill in the timestamp value.
310 
311 
312 ### OCSD_GEN_TRC_ELEM_CUSTOM ###
313 __packet fields optional__: `extended_data -> ptr_extended_data`,_any others_
314 
315 Custom protocol decoders can use this packet type to provide protocol specific information.
316 
317 Standard fields may be used for similar purposes as defined above, or the extended data pointer can reference
318 other data.
319 
320 --------------------------------------------------------------------------------------------------
321 
322 Generic Trace Packets - Notes on interpretation.
323 ------------------------------------------------
324 
325 The interpretation of the trace output should always be done with reference to the underlying protocol
326 specifications.
327 
328 While the output packets are in general protocol agnostic, there are some inevitable
329 differences related to the underlying protocol that stem from the development of the trace hardware over time.
330 
331 ### OCSD ranges and Trace Atom Packets ###
332 The most common raw trace packet in all the protocols is the Atom packet, and this packet is the basis for most of
333 the `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packets output from the library. A trace range will be output for each atom
334 in the raw trace stream - the `last_instr_exec` flag taking the value of the Atom - 1 for E, 0 for N.
335 
336 `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packets can also be generated for non-atom packets, where flow changes - e.g.
337 exceptions.
338 
339 
340 ### Multi feature OCSD output packets ###
341 Where a raw trace packet contains additional information on top of the basic packet data, then this additional
342 information will be added to the OCSD output packet and flagged accordingly (in the `flag_bits` union in the
343 packet structure).
344 
345 Typically this will be atom+cycle count packets in ETMv3 and PTM protocols. For efficiency and to retain
346 the coupling between the information an `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packet will be output in this case
347 with a `has_cc` flag set and the `cycle_count` value filled.
348 
349 ETMv3 and PTM can add a cycle count to a number of packets, or explicitly emit a cycle count only packet. By
350 contrast ETMv4 only emits cycle count only packets.
351 
352 Clients processing the library output must be aware of these optional additions to the base packet. The
353 OCSD packet descriptions above outline where the additional information can occur.
354 
355 ### Cycle counts ###
356 
357 Cycle counts are cumulative, and represent cycles since the last cycle count output.
358 Explicit cycle count packets are associated with the previous range event, otherwise where a
359 packet includes a cycle count as additional information, then the count is associated with that
360 specific packet - which will often be a range packet.
361 
362 The only exception to this is where the underlying protocol is ETMv4, and a cycle count is included
363 in a timestamp packet. Here the cycle count represents that number of cycles since the last cycle count
364 packet that occurred before the timestamp packet was emitted. This cycle count is not part of the cumulative
365 count. See the ETMv4 specification for further details.
366 
367 
368 ### Correlation - timestamps and cycle counts ###
369 
370 Different trace streams can be correlated using either timestamps, or timestamps plus cycle counts.
371 
372 Both timestamps and cycle counts are enabled by programming ETM control registers, and it is also possible
373 to control the frequency that timestamps appear, or the threshold at which cycle count packets are emitted by
374 additional programming.
375 
376 The output of timestamps and cycle counts increases the amount of trace generated, very significantly when cycle
377 counts are present, so the choice of generating these elements needs to be balanced against the requirement
378 for their use.
379 
380 Decent correlation can be gained by the use of timestamps alone - especially if the source is programmed to
381 produce them more frequently than the default timestamp events. More precise correllation can be performed if
382 the 'gaps' between timestamps can be resolved using cycle counts.
383 
384 Correlation is performed by identifying the same/close timestamp values in two separate trace streams. Cycle counts
385 if present can then be used to resolve the correlation with additional accuracy.
386 
387 
388 
389 
390 
391 
392 
393 
394 
395 
396