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| -rw-r--r-- | Documentation/trace/coresight.txt | 299 |
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diff --git a/Documentation/trace/coresight.txt b/Documentation/trace/coresight.txt new file mode 100644 index 000000000000..bba7dbfc49ed --- /dev/null +++ b/Documentation/trace/coresight.txt @@ -0,0 +1,299 @@ + Coresight - HW Assisted Tracing on ARM + ====================================== + + Author: Mathieu Poirier <mathieu.poirier@linaro.org> + Date: September 11th, 2014 + +Introduction +------------ + +Coresight is an umbrella of technologies allowing for the debugging of ARM +based SoC. It includes solutions for JTAG and HW assisted tracing. This +document is concerned with the latter. + +HW assisted tracing is becoming increasingly useful when dealing with systems +that have many SoCs and other components like GPU and DMA engines. ARM has +developed a HW assisted tracing solution by means of different components, each +being added to a design at systhesis time to cater to specific tracing needs. +Compoments are generally categorised as source, link and sinks and are +(usually) discovered using the AMBA bus. + +"Sources" generate a compressed stream representing the processor instruction +path based on tracing scenarios as configured by users. From there the stream +flows through the coresight system (via ATB bus) using links that are connecting +the emanating source to a sink(s). Sinks serve as endpoints to the coresight +implementation, either storing the compressed stream in a memory buffer or +creating an interface to the outside world where data can be transferred to a +host without fear of filling up the onboard coresight memory buffer. + +At typical coresight system would look like this: + + ***************************************************************** + **************************** AMBA AXI ****************************===|| + ***************************************************************** || + ^ ^ | || + | | * ** + 0000000 ::::: 0000000 ::::: ::::: @@@@@@@ |||||||||||| + 0 CPU 0<-->: C : 0 CPU 0<-->: C : : C : @ STM @ || System || + |->0000000 : T : |->0000000 : T : : T :<--->@@@@@ || Memory || + | #######<-->: I : | #######<-->: I : : I : @@@<-| |||||||||||| + | # ETM # ::::: | # PTM # ::::: ::::: @ | + | ##### ^ ^ | ##### ^ ! ^ ! . | ||||||||| + | |->### | ! | |->### | ! | ! . | || DAP || + | | # | ! | | # | ! | ! . | ||||||||| + | | . | ! | | . | ! | ! . | | | + | | . | ! | | . | ! | ! . | | * + | | . | ! | | . | ! | ! . | | SWD/ + | | . | ! | | . | ! | ! . | | JTAG + *****************************************************************<-| + *************************** AMBA Debug ABP ************************ + ***************************************************************** + | . ! . ! ! . | + | . * . * * . | + ***************************************************************** + ******************** Cross Trigger Matrix (CTM) ******************* + ***************************************************************** + | . ^ . . | + | * ! * * | + ***************************************************************** + ****************** AMBA Advanced Trace Bus (ATB) ****************** + ***************************************************************** + | ! =============== | + | * ===== F =====<---------| + | ::::::::: ==== U ==== + |-->:: CTI ::<!! === N === + | ::::::::: ! == N == + | ^ * == E == + | ! &&&&&&&&& IIIIIII == L == + |------>&& ETB &&<......II I ======= + | ! &&&&&&&&& II I . + | ! I I . + | ! I REP I<.......... + | ! I I + | !!>&&&&&&&&& II I *Source: ARM ltd. + |------>& TPIU &<......II I DAP = Debug Access Port + &&&&&&&&& IIIIIII ETM = Embedded Trace Macrocell + ; PTM = Program Trace Macrocell + ; CTI = Cross Trigger Interface + * ETB = Embedded Trace Buffer + To trace port TPIU= Trace Port Interface Unit + SWD = Serial Wire Debug + +While on target configuration of the components is done via the ABP bus, +all trace data are carried out-of-band on the ATB bus. The CTM provides +a way to aggregate and distribute signals between CoreSight components. + +The coresight framework provides a central point to represent, configure and +manage coresight devices on a platform. This first implementation centers on +the basic tracing functionality, enabling components such ETM/PTM, funnel, +replicator, TMC, TPIU and ETB. Future work will enable more +intricate IP blocks such as STM and CTI. + + +Acronyms and Classification +--------------------------- + +Acronyms: + +PTM: Program Trace Macrocell +ETM: Embedded Trace Macrocell +STM: System trace Macrocell +ETB: Embedded Trace Buffer +ITM: Instrumentation Trace Macrocell +TPIU: Trace Port Interface Unit +TMC-ETR: Trace Memory Controller, configured as Embedded Trace Router +TMC-ETF: Trace Memory Controller, configured as Embedded Trace FIFO +CTI: Cross Trigger Interface + +Classification: + +Source: + ETMv3.x ETMv4, PTMv1.0, PTMv1.1, STM, STM500, ITM +Link: + Funnel, replicator (intelligent or not), TMC-ETR +Sinks: + ETBv1.0, ETB1.1, TPIU, TMC-ETF +Misc: + CTI + + +Device Tree Bindings +---------------------- + +See Documentation/devicetree/bindings/arm/coresight.txt for details. + +As of this writing drivers for ITM, STMs and CTIs are not provided but are +expected to be added as the solution matures. + + +Framework and implementation +---------------------------- + +The coresight framework provides a central point to represent, configure and +manage coresight devices on a platform. Any coresight compliant device can +register with the framework for as long as they use the right APIs: + +struct coresight_device *coresight_register(struct coresight_desc *desc); +void coresight_unregister(struct coresight_device *csdev); + +The registering function is taking a "struct coresight_device *csdev" and +register the device with the core framework. The unregister function takes +a reference to a "strut coresight_device", obtained at registration time. + +If everything goes well during the registration process the new devices will +show up under /sys/bus/coresight/devices, as showns here for a TC2 platform: + +root:~# ls /sys/bus/coresight/devices/ +replicator 20030000.tpiu 2201c000.ptm 2203c000.etm 2203e000.etm +20010000.etb 20040000.funnel 2201d000.ptm 2203d000.etm +root:~# + +The functions take a "struct coresight_device", which looks like this: + +struct coresight_desc { + enum coresight_dev_type type; + struct coresight_dev_subtype subtype; + const struct coresight_ops *ops; + struct coresight_platform_data *pdata; + struct device *dev; + const struct attribute_group **groups; +}; + + +The "coresight_dev_type" identifies what the device is, i.e, source link or +sink while the "coresight_dev_subtype" will characterise that type further. + +The "struct coresight_ops" is mandatory and will tell the framework how to +perform base operations related to the components, each component having +a different set of requirement. For that "struct coresight_ops_sink", +"struct coresight_ops_link" and "struct coresight_ops_source" have been +provided. + +The next field, "struct coresight_platform_data *pdata" is acquired by calling +"of_get_coresight_platform_data()", as part of the driver's _probe routine and +"struct device *dev" gets the device reference embedded in the "amba_device": + +static int etm_probe(struct amba_device *adev, const struct amba_id *id) +{ + ... + ... + drvdata->dev = &adev->dev; + ... +} + +Specific class of device (source, link, or sink) have generic operations +that can be performed on them (see "struct coresight_ops"). The +"**groups" is a list of sysfs entries pertaining to operations +specific to that component only. "Implementation defined" customisations are +expected to be accessed and controlled using those entries. + +Last but not least, "struct module *owner" is expected to be set to reflect +the information carried in "THIS_MODULE". + +How to use +---------- + +Before trace collection can start, a coresight sink needs to be identify. +There is no limit on the amount of sinks (nor sources) that can be enabled at +any given moment. As a generic operation, all device pertaining to the sink +class will have an "active" entry in sysfs: + +root:/sys/bus/coresight/devices# ls +replicator 20030000.tpiu 2201c000.ptm 2203c000.etm 2203e000.etm +20010000.etb 20040000.funnel 2201d000.ptm 2203d000.etm +root:/sys/bus/coresight/devices# ls 20010000.etb +enable_sink status trigger_cntr +root:/sys/bus/coresight/devices# echo 1 > 20010000.etb/enable_sink +root:/sys/bus/coresight/devices# cat 20010000.etb/enable_sink +1 +root:/sys/bus/coresight/devices# + +At boot time the current etm3x driver will configure the first address +comparator with "_stext" and "_etext", essentially tracing any instruction +that falls within that range. As such "enabling" a source will immediately +trigger a trace capture: + +root:/sys/bus/coresight/devices# echo 1 > 2201c000.ptm/enable_source +root:/sys/bus/coresight/devices# cat 2201c000.ptm/enable_source +1 +root:/sys/bus/coresight/devices# cat 20010000.etb/status +Depth: 0x2000 +Status: 0x1 +RAM read ptr: 0x0 +RAM wrt ptr: 0x19d3 <----- The write pointer is moving +Trigger cnt: 0x0 +Control: 0x1 +Flush status: 0x0 +Flush ctrl: 0x2001 +root:/sys/bus/coresight/devices# + +Trace collection is stopped the same way: + +root:/sys/bus/coresight/devices# echo 0 > 2201c000.ptm/enable_source +root:/sys/bus/coresight/devices# + +The content of the ETB buffer can be harvested directly from /dev: + +root:/sys/bus/coresight/devices# dd if=/dev/20010000.etb \ +of=~/cstrace.bin + +64+0 records in +64+0 records out +32768 bytes (33 kB) copied, 0.00125258 s, 26.2 MB/s +root:/sys/bus/coresight/devices# + +The file cstrace.bin can be decompressed using "ptm2human", DS-5 or Trace32. + +Following is a DS-5 output of an experimental loop that increments a variable up +to a certain value. The example is simple and yet provides a glimpse of the +wealth of possibilities that coresight provides. + +Info Tracing enabled +Instruction 106378866 0x8026B53C E52DE004 false PUSH {lr} +Instruction 0 0x8026B540 E24DD00C false SUB sp,sp,#0xc +Instruction 0 0x8026B544 E3A03000 false MOV r3,#0 +Instruction 0 0x8026B548 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Timestamp Timestamp: 17106715833 +Instruction 319 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 9 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 7 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 7 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 10 0x8026B54C E59D3004 false LDR r3,[sp,#4] +Instruction 0 0x8026B550 E3530004 false CMP r3,#4 +Instruction 0 0x8026B554 E2833001 false ADD r3,r3,#1 +Instruction 0 0x8026B558 E58D3004 false STR r3,[sp,#4] +Instruction 0 0x8026B55C DAFFFFFA true BLE {pc}-0x10 ; 0x8026b54c +Instruction 6 0x8026B560 EE1D3F30 false MRC p15,#0x0,r3,c13,c0,#1 +Instruction 0 0x8026B564 E1A0100D false MOV r1,sp +Instruction 0 0x8026B568 E3C12D7F false BIC r2,r1,#0x1fc0 +Instruction 0 0x8026B56C E3C2203F false BIC r2,r2,#0x3f +Instruction 0 0x8026B570 E59D1004 false LDR r1,[sp,#4] +Instruction 0 0x8026B574 E59F0010 false LDR r0,[pc,#16] ; [0x8026B58C] = 0x80550368 +Instruction 0 0x8026B578 E592200C false LDR r2,[r2,#0xc] +Instruction 0 0x8026B57C E59221D0 false LDR r2,[r2,#0x1d0] +Instruction 0 0x8026B580 EB07A4CF true BL {pc}+0x1e9344 ; 0x804548c4 +Info Tracing enabled +Instruction 13570831 0x8026B584 E28DD00C false ADD sp,sp,#0xc +Instruction 0 0x8026B588 E8BD8000 true LDM sp!,{pc} +Timestamp Timestamp: 17107041535 |