1 OpenCSD Library - Generic Trace Packet Descriptions {#generic_pkts}
2 ===================================================
4 @brief Interpretation of the Generic Trace output packets.
6 Generic Trace Packets - Collection.
7 -----------------------------------
9 ### Packet interface ###
11 The generic trace packets are the fully decoded output from the trace library.
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.
16 The callback is in the form of an interface class ITrcGenElemIn, which has a single function:
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
25 The client program will create derived class providing this interface to collect trace packets from the library.
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. |
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.
37 The C-API provides a similarly specified callback function definition, with an additional opaque `void *` pointer
38 that the client application may use.
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);
48 ### The Packet Structure ###
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 */
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 */
77 //! packet specific payloads
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) */
87 const void *ptr_extended_data; /* pointer to extended data buffer (data trace, sw trace payload) / custom structure */
89 } ocsd_generic_trace_elem;
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.
96 The packet reference guide below defines the fields valid for each packet type.
98 --------------------------------------------------------------------------------------------------
100 Generic Trace Packets - Packet Reference.
101 -----------------------------------------
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.
106 The descriptions will include information on which fields in the packets are always valid, optional and any protocol specific information.
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.
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
118 ### OCSD_GEN_TRC_ELEM_NO_SYNC ###
119 __packet fields valid__: None
121 Element output before the decoder has synchronised with the input stream, or synchronisation is lost.
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`
126 __packet fields optional__: `has_cc -> cycle_count,`
128 __protocol specific__ : ETMv3, PTM
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`.
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.
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.
143 ### OCSD_GEN_TRC_ELEM_ADDR_NACC ###
144 __packet fields valid__: `st_addr`
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.
149 Decoder will wait for new address to appear in trace before attempting to restart decoding.
152 ### OCSD_GEN_TRC_ELEM_UNKNOWN ###
153 __packet fields valid__: None
155 Decoder saw invalid packet for protocol being processed. Likely incorrect protocol settings, or corrupted
158 ### OCSD_GEN_TRC_ELEM_TRACE_ON ###
159 __packet fields valid__: trace_on_reason
161 __packet fields optional__: `has_cc -> cycle_count,`
163 __protocol specific__ : ETMv3, PTM
165 Notification that trace has started / is synced after a discontinuity or at start of trace decode.
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.
171 ### OCSD_GEN_TRC_ELEM_EO_TRACE ###
172 __packet fields valid__: None
174 Marker for end of trace data. Sent once for each CoreSight ID channel.
176 ### OCSD_GEN_TRC_ELEM_PE_CONTEXT ###
177 __packet fields valid__: context
179 __packet fields optional__: `has_cc -> cycle_count,`
181 __protocol specific__ : ETMv3, PTM
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.
186 The context is contained in a `ocsd_pe_context` structure.
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 */
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) */
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.
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`.
210 ### OCSD_GEN_TRC_ELEM_ADDR_UNKNOWN ###
211 __packet fields optional__: `has_cc -> cycle_count,`
213 __protocol specific__: ETMv3
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.
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.
223 ### OCSD_GEN_TRC_ELEM_EXCEPTION ###
224 __packet fields valid__: `exception_number`
226 __packet fields optional__: `has_cc -> cycle_count, excep_ret_addr -> en_addr, excep_data_marker`
228 __protocol specific__: ETMv4, ETMv3, PTM
230 All protocols will include the exception number in the packet.
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.
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.
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.
242 ### OCSD_GEN_TRC_ELEM_EXCEPTION_RET ###
243 __packet fields valid__: None
245 Marker that a preceding branch was an exception return.
247 ### OCSD_GEN_TRC_ELEM_TIMESTAMP ###
248 __packet fields valid__: `timestamp`
250 __packet fields optional__: `has_cc -> cycle_count,`
252 __protocol specific__: ETMv4, PTM
254 The timestamp packet explicitly provides a timestamp value for the trace stream ID in the callback interface.
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.
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.
264 ### OCSD_GEN_TRC_ELEM_CYCLE_COUNT ###
265 __packet fields valid__: `has_cc -> cycle_count`
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.
271 Cycle count packets may be added together to build a cumulative count for the trace session.
273 ### OCSD_GEN_TRC_ELEM_EVENT ###
274 __packet fields valid__: `trace_event`
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.
279 The `trace_event` is a `trace_event_t` structure that can have an event type - and an event number.
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 */
288 The event types depend on the trace hardware:-
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.
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.
296 __PTM__, __ETMv3__ : produce trigger events. Event number always set to 0.
299 ### OCSD_GEN_TRC_ELEM_SWTRACE ###
300 __packet fields valid__: `sw_trace_info`
302 __packet fields optional__: `has_ts -> timestamp`, ` extended_data -> ptr_extended_data`
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.
307 SW trace packets that have a payload will use the extended_data flag and pointer to deliver this data.
309 SW trace packets that include timestamp information will us the `has_ts` flag and fill in the timestamp value.
312 ### OCSD_GEN_TRC_ELEM_CUSTOM ###
313 __packet fields optional__: `extended_data -> ptr_extended_data`,_any others_
315 Custom protocol decoders can use this packet type to provide protocol specific information.
317 Standard fields may be used for similar purposes as defined above, or the extended data pointer can reference
320 --------------------------------------------------------------------------------------------------
322 Generic Trace Packets - Notes on interpretation.
323 ------------------------------------------------
325 The interpretation of the trace output should always be done with reference to the underlying protocol
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.
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.
336 `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packets can also be generated for non-atom packets, where flow changes - e.g.
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
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.
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.
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.
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.
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.
368 ### Correlation - timestamps and cycle counts ###
370 Different trace streams can be correlated using either timestamps, or timestamps plus cycle counts.
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.
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
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.
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.