1OpenCSD Library - Generic Trace Packet Descriptions {#generic_pkts} 2=================================================== 3 4@brief Interpretation of the Generic Trace output packets. 5 6Generic Trace Packets - Collection. 7----------------------------------- 8 9### Packet interface ### 10 11The generic trace packets are the fully decoded output from the trace library. 12 13These are delivered to the client application in the form of a callback function. Packets from all trace sources 14will use the same single callback function, with the CoreSight Trace ID provided to identify the source. 15 16The callback is in the form of an interface class ITrcGenElemIn, which has a single function: 17 18~~~{.cpp} 19virtual 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 25The client program will create derived class providing this interface to collect trace packets from the library. 26 27The 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 35can represent multiple atoms and hence multiple ranges. 36 37The C-API provides a similarly specified callback function definition, with an additional opaque `void *` pointer 38that the client application may use. 39 40~~~{.c} 41/** function pointer type for decoder outputs. all protocols, generic data element input */ 42typedef 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} 51typedef 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 uint32_t last_instr_cond:1; /* 1 if the last instruction was conditional */ 74 uint32_t excep_ret_addr_br_tgt:1; /* 1 if exception return address (en_addr) is also the target of a taken branch addr from the previous range. */ 75 uint32_t excep_M_tail_chain:1; /* 1 if the exception is an M class exception with no pref ret address - tail chained or similar */ 76 77 }; 78 uint32_t flag_bits; 79 }; 80 81 //! packet specific payloads 82 union { 83 uint32_t exception_number; /* exception number for exception type packets */ 84 trace_event_t trace_event; /* Trace event - trigger etc */ 85 trace_on_reason_t trace_on_reason; /* reason for the trace on packet */ 86 ocsd_swt_info_t sw_trace_info; /* software trace packet info */ 87 uint32_t num_instr_range; /* number of instructions covered by range packet (for T32 this cannot be calculated from en-st/i_size) */ 88 unsync_info_t unsync_eot_info; /* additional information for unsync / end-of-trace packets. */ 89 trace_marker_payload_t sync_marker; /* marker element - sync later element to position in stream */ 90 trace_memtrans_t mem_trans; /* memory transaction packet - transaction event */ 91 trace_sw_ite_t sw_ite; /* PE sw instrumentation using FEAT_ITE */ 92 93 }; 94 95 const void *ptr_extended_data; /* pointer to extended data buffer (data trace, sw trace payload) / custom structure */ 96 97} ocsd_generic_trace_elem; 98~~~ 99 100The packet structure contains multiple fields and flag bits. The validity of any of these fields or flags 101is dependent on the `elem_type` member. The client program must not assume that field values will persist 102between packets, and must process all valid data during the callback function. 103 104The packet reference guide below defines the fields valid for each packet type. 105 106-------------------------------------------------------------------------------------------------- 107 108Generic Trace Packets - Packet Reference. 109----------------------------------------- 110 111This section contains reference descriptions of each of the generic trace packets types define as part of the 112`ocsd_gen_trc_elem_t` enum value that appears as the first `elem_type` field in the packet structure. 113 114The descriptions will include information on which fields in the packets are always valid, optional and any protocol specific information. 115 116The tags used in the reference are:- 117- __packet fields valid__ : fields that are always valid and filled for this packet type. 118- __packet fields optional__ : fields that _may_ be filled for this packet type. 119 The form `flag -> field` indicates a flag that may be set and the value that is valid if the flag is true 120- __protocol specific__ : indicates type or fields may be source protocol specific. 121 122_Note_: while most of the packets are not protocol specific, there are some protocol differences that mean 123certain types and fields will differ slightly across protocols. These differences are highlighted in the 124reference. 125 126### OCSD_GEN_TRC_ELEM_NO_SYNC ### 127__packet fields valid__: None 128 129Element output before the decoder has synchronised with the input stream, or synchronisation is lost. 130 131### OCSD_GEN_TRC_ELEM_INSTR_RANGE ### 132__packet fields valid__: `isa, st_addr, en_addr, last_i_type, last_i_subtype, last_instr_exec, last_instr_sz, num_instr_range, last_instr_cond` 133 134__packet fields optional__: `has_cc -> cycle_count,` 135 136__protocol specific__ : ETMv3, PTM 137 138This should be the most common packet output for full trace decode. Represents a range of instructions of 139a single `isa`, executed by the PE. Instruction byte range is from `st_addr` (inclusive) to `en_addr` (exclusive). 140The total number of instructions executed for the range is given in `num_instr_range`. 141 142Information on the last instruction in the range is provided. `last_i_type` shows if the last instruction 143was a branch or otherwise - which combined with `last_instr_exec` determines if the branch was taken. 144The last instruction size in bytes is given, to allow clients to quickly determine the address of the last 145instruction by subtraction from `en_addr`. This value can be 2 or 4 bytes in the T32 instruction set. 146 147__ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates 148the trace range. In this case `has_cc` will be 1 and `cycle_count` will be valid. 149 150 151### OCSD_GEN_TRC_ELEM_I_RANGE_NOPATH ### 152__packet fields valid__: `isa, st_addr, en_addr, num_instr_range` 153 154`num_instr_range` represents the number of instructions executed in this range, but there is incomplete information 155as to program execution path from start to end of range. 156If `num_instr` is 0, then an unknown number of instructions were executed between the start and end of the range. 157`st_addr` represents the start of execution represented by this packet. 158`en_addr` represents the address where execution will continue from after the instructions represented by this packet. 159`isa` represents the ISA for the instruction at `en_addr`. 160 161Used when ETMv4 Q elements are being traced. 162 163 164### OCSD_GEN_TRC_ELEM_ADDR_NACC ### 165__packet fields valid__: `st_addr` 166 167Trace decoder found address in trace that cannot be accessed in the mapped memory images. 168`st_addr` is the address that cannot be found. 169 170Decoder will wait for new address to appear in trace before attempting to restart decoding. 171 172 173### OCSD_GEN_TRC_ELEM_UNKNOWN ### 174__packet fields valid__: None 175 176Decoder saw invalid packet for protocol being processed. Likely incorrect protocol settings, or corrupted 177trace data. 178 179### OCSD_GEN_TRC_ELEM_TRACE_ON ### 180__packet fields valid__: trace_on_reason 181 182__packet fields optional__: `has_cc -> cycle_count,` 183 184__protocol specific__ : ETMv3, PTM 185 186Notification that trace has started / is synced after a discontinuity or at start of trace decode. 187 188__ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates 189the trace on indicator. In this case `has_cc` will be 1 and `cycle_count` will be valid. 190 191 192### OCSD_GEN_TRC_ELEM_EO_TRACE ### 193__packet fields valid__: None 194 195Marker for end of trace data. Sent once for each CoreSight ID channel. 196 197### OCSD_GEN_TRC_ELEM_PE_CONTEXT ### 198__packet fields valid__: context 199 200__packet fields optional__: `has_cc -> cycle_count,` 201 202__protocol specific__ : ETMv3, PTM 203 204This packet indicates an update to the PE context - which may be the initial context in a trace stream, or a 205change since the trace started. 206 207The context is contained in a `ocsd_pe_context` structure. 208 209~~~{.c} 210typedef struct _ocsd_pe_context { 211 ocsd_sec_level security_level; /* security state */ 212 ocsd_ex_level exception_level; /* exception level */ 213 uint32_t context_id; /* context ID */ 214 uint32_t vmid; /* VMID */ 215 struct { 216 uint32_t bits64:1; /* 1 if 64 bit operation */ 217 uint32_t ctxt_id_valid:1; /* 1 if context ID value valid */ 218 uint32_t vmid_valid:1; /* 1 if VMID value is valid */ 219 uint32_t el_valid:1; /* 1 if EL value is valid (ETMv4 traces current EL, other protocols do not) */ 220 }; 221} ocsd_pe_context; 222~~~ 223 224__ETMv3, PTM__ : These protocols can output a cycle count directly as part of the trace packet that generates 225the PE context. In this case `has_cc` will be 1 and `cycle_count` will be valid. 226 227__ETMv3__ : From ETM 3.5 onwards, exception_level can be set to `ocsd_EL2` when tracing through hypervisor code. 228On all other occasions this will be set to `ocsd_EL_unknown`. 229 230 231### OCSD_GEN_TRC_ELEM_ADDR_UNKNOWN ### 232__packet fields optional__: `has_cc -> cycle_count,` 233 234__protocol specific__: ETMv3 235 236This packet will only be seen when decoding an ETMv3 protocol source. This indicates that the decoder 237is waiting for a valid address in order to process trace correctly. 238 239The packet can have a cycle count associated with it which the client must account for when tracking cycles used. 240The packet will be sent once when unknown address occurs. Further `OCSD_GEN_TRC_ELEM_CYCLE_COUNT` packets may follow 241 before the decode receives a valid address to continue decode. 242 243 244### OCSD_GEN_TRC_ELEM_EXCEPTION ### 245__packet fields valid__: `exception_number` 246 247__packet fields optional__: `has_cc -> cycle_count, excep_ret_addr -> en_addr, excep_data_marker, excep_ret_addr_br_tgt, excep_M_tail_chain` 248 249__protocol specific__: ETMv4, ETMv3, PTM 250 251All protocols will include the exception number in the packet. 252 253__ETMv4__ : This protocol may provide the preferred return address for the exception - this is the address of 254the instruction that could be executed on exception return. This address appears in `en_addr` if `excep_ret_addr` = 1. 255 256Additionally, this address could also represent the target address of a branch, if the exception occured at the branch target, before any further 257instructions were executed. If this is the case then the excep_ret_addr_br_tgt flag will be set. This makes explicit what was previously only implied by teh packet ordered. This information could be used for clients such as perf that branch source/target address pairs. 258 259Where `excep_M_tail_chain == 1`, the exception was the result of M profile exception tail chaining, or similar M profile 260events indicated by a standard address value, where the value is not the preferred return address. 261 262__ETMv3__ : This can set the `excep_data_marker` flag. This indicates that the exception packet is a marker 263to indicate exception entry in a 7M profile core, for the purposes of tracking data. This will __not__ provide 264an exception number in this case. 265 266__PTM__ : Can have an associated cycle count (`has_cc == 1`), and may provide preferred return address in `en_addr` 267if `excep_ret_addr` = 1. 268 269### OCSD_GEN_TRC_ELEM_EXCEPTION_RET ### 270__packet fields valid__: None 271 272Marker that a preceding branch was an exception return. 273 274### OCSD_GEN_TRC_ELEM_TIMESTAMP ### 275__packet fields valid__: `timestamp` 276 277__packet fields optional__: `has_cc -> cycle_count,` 278 279__protocol specific__: ETMv4, PTM 280 281The timestamp packet explicitly provides a timestamp value for the trace stream ID in the callback interface. 282 283__PTM__ : This can have an associated cycle count (`has_cc == 1`). For this protocol, the cycle count __is__ part 284of the cumulative cycle count for the trace session. 285 286__ETMv4__ : This can have an associated cycle count (`has_cc == 1`). For this protocl, the cycle coun represents 287the number of cycles between the previous cycle count packet and this timestamp packet, but __is not__ part of 288the cumulative cycle count for the trace session. 289 290 291### OCSD_GEN_TRC_ELEM_CYCLE_COUNT ### 292__packet fields valid__: `has_cc -> cycle_count` 293 294Packet contains a cycle count value. A cycle count value represents the number of cycles passed since the 295last cycle count value seen. The cycle count value may be associated with a specific packet or instruction 296range preceding the cycle count packet. 297 298Cycle count packets may be added together to build a cumulative count for the trace session. 299 300### OCSD_GEN_TRC_ELEM_EVENT ### 301__packet fields valid__: `trace_event` 302 303This is a hardware event injected into the trace by the ETM/PTM hardware resource programming. See the 304relevent trace hardware reference manuals for the programming of these events. 305 306The `trace_event` is a `trace_event_t` structure that can have an event type - and an event number. 307 308~~~{.c} 309typedef struct _trace_event_t { 310 uint16_t ev_type; /* event type - unknown (0) trigger (1), numbered event (2)*/ 311 uint16_t ev_number; /* event number if numbered event type */ 312} trace_event_t; 313~~~ 314 315The event types depend on the trace hardware:- 316 317__ETMv4__ : produces numbered events. The event number is a bitfield of up to four events that occurred. 318Events 0-3 -> bits 0-3. The bitfield allows a single packet to represent multiple different events occurring. 319 320_Note_: The ETMv4 specification has further information on timing of events and event packets. Event 0 321is also considered a trigger event in ETMv4 hardware, but is not explicitly represented as such in the OCSD protocol. 322 323__PTM__, __ETMv3__ : produce trigger events. Event number always set to 0. 324 325 326### OCSD_GEN_TRC_ELEM_SWTRACE ### 327__packet fields valid__: `sw_trace_info` 328 329__packet fields optional__: `has_ts -> timestamp`, ` extended_data -> ptr_extended_data` 330 331The Software trace packet always has a filled in `sw_trace_info` field to describe the current master and channel ID, 332plus the packet type and size of any payload data. 333 334SW trace packets that have a payload will use the extended_data flag and pointer to deliver this data. 335 336SW trace packets that include timestamp information will us the `has_ts` flag and fill in the timestamp value. 337 338These packets are generated by memory writes to STM / ITM trace hardware. 339 340### OCSD_GEN_TRC_ELEM_SYNC_MARKER ### 341__packet fields valid__: `sync_marker` 342 343Synchronisation marker - marks position in stream of an element that is output later. 344e.g. a timestamp marker can be output to represent the correct position in the stream for a 345timestamp packet the is output later. 346 347The `sync_marker` field has a structure as shown below. 348 349~~~{.c} 350typedef enum _trace_sync_marker_t { 351 ELEM_MARKER_TS, /**< Marker for timestamp element */ 352} trace_sync_marker_t; 353 354typedef struct _trace_marker_payload_t { 355 trace_sync_marker_t type; /**< type of sync marker */ 356 uint32_t value; /**< sync marker value - usage depends on type */ 357} trace_marker_payload_t; 358~~~ 359 360### OCSD_GEN_TRC_ELEM_MEMTRANS ### 361__packet fields valid__: `mem_trans` 362 363Memory transaction elements may appear in the output stream, if they are not otherwise cancelled 364by speculative trace packets. 365 366The memory transaction field has values as defined in the enum below:- 367 368~~~{.c} 369typedef enum _memtrans_t { 370 OCSD_MEM_TRANS_TRACE_INIT,/* Trace started while PE in transactional state */ 371 OCSD_MEM_TRANS_START, /* Trace after this packet is part of a transactional memory sequence */ 372 OCSD_MEM_TRANS_COMMIT, /* Transactional memory sequence valid. */ 373 OCSD_MEM_TRANS_FAIL, /* Transactional memory sequence failed - operations since start of transaction have been unwound. */ 374} trace_memtrans_t; 375~~~ 376 377### OCSD_GEN_TRC_ELEM_INSTRUMENTATION ### 378__packet fields valid__: `sw_ite` 379 380Software instrumentation packets generated by the PE `TRCIT` instruction (on cores with `FEAT_ITE`). 381 382The `sw_ite` structure has the fields defined below:- 383 384~~~{.c} 385typedef struct _sw_ite_t { 386 uint8_t el; /* exception level for PE sw instrumentation instruction */ 387 uint64_t value; /* payload for PE sw instrumentation instruction */ 388} trace_sw_ite_t; 389~~~ 390 391### OCSD_GEN_TRC_ELEM_CUSTOM ### 392__packet fields optional__: `extended_data -> ptr_extended_data`,_any others_ 393 394Custom protocol decoders can use this packet type to provide protocol specific information. 395 396Standard fields may be used for similar purposes as defined above, or the extended data pointer can reference 397other data. 398 399-------------------------------------------------------------------------------------------------- 400 401Generic Trace Packets - Notes on interpretation. 402------------------------------------------------ 403 404The interpretation of the trace output should always be done with reference to the underlying protocol 405specifications. 406 407While the output packets are in general protocol agnostic, there are some inevitable 408differences related to the underlying protocol that stem from the development of the trace hardware over time. 409 410### OCSD ranges and Trace Atom Packets ### 411The most common raw trace packet in all the protocols is the Atom packet, and this packet is the basis for most of 412the `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packets output from the library. A trace range will be output for each atom 413in the raw trace stream - the `last_instr_exec` flag taking the value of the Atom - 1 for E, 0 for N. 414 415`OCSD_GEN_TRC_ELEM_INSTR_RANGE` packets can also be generated for non-atom packets, where flow changes - e.g. 416exceptions. 417 418 419### Multi feature OCSD output packets ### 420Where a raw trace packet contains additional information on top of the basic packet data, then this additional 421information will be added to the OCSD output packet and flagged accordingly (in the `flag_bits` union in the 422packet structure). 423 424Typically this will be atom+cycle count packets in ETMv3 and PTM protocols. For efficiency and to retain 425the coupling between the information an `OCSD_GEN_TRC_ELEM_INSTR_RANGE` packet will be output in this case 426with a `has_cc` flag set and the `cycle_count` value filled. 427 428ETMv3 and PTM can add a cycle count to a number of packets, or explicitly emit a cycle count only packet. By 429contrast ETMv4 only emits cycle count only packets. 430 431Clients processing the library output must be aware of these optional additions to the base packet. The 432OCSD packet descriptions above outline where the additional information can occur. 433 434### Cycle counts ### 435 436Cycle counts are cumulative, and represent cycles since the last cycle count output. 437Explicit cycle count packets are associated with the previous range event, otherwise where a 438packet includes a cycle count as additional information, then the count is associated with that 439specific packet - which will often be a range packet. 440 441The only exception to this is where the underlying protocol is ETMv4, and a cycle count is included 442in a timestamp packet. Here the cycle count represents that number of cycles since the last cycle count 443packet that occurred before the timestamp packet was emitted. This cycle count is not part of the cumulative 444count. See the ETMv4 specification for further details. 445 446 447### Correlation - timestamps and cycle counts ### 448 449Different trace streams can be correlated using either timestamps, or timestamps plus cycle counts. 450 451Both timestamps and cycle counts are enabled by programming ETM control registers, and it is also possible 452to control the frequency that timestamps appear, or the threshold at which cycle count packets are emitted by 453additional programming. 454 455The output of timestamps and cycle counts increases the amount of trace generated, very significantly when cycle 456counts are present, so the choice of generating these elements needs to be balanced against the requirement 457for their use. 458 459Decent correlation can be gained by the use of timestamps alone - especially if the source is programmed to 460produce them more frequently than the default timestamp events. More precise correllation can be performed if 461the 'gaps' between timestamps can be resolved using cycle counts. 462 463Correlation is performed by identifying the same/close timestamp values in two separate trace streams. Cycle counts 464if present can then be used to resolve the correlation with additional accuracy. 465 466 467 468 469 470 471 472 473 474 475 476