Improve efficiency and formatting of ITM output #7371

kjbracey · 2018-06-29T09:45:52Z

Description

SerialWireOutput was outputting 1 character per 32-bit write to the ITM stimulus port. This is inefficient, and causes processing problems with some viewers due to them receiving 3 NUL bytes between each desired character.

Rework to allow us to be more efficient, and eliminate those NUL bytes:

Retain existing mbed_itm_send() and clarify it's a single 32-bit write.
Add new mbed_itm_send_block() that is appropriate for sending character data, and modify SerialWireOutput to use it.
Move "wait for FIFO ready" check to before the write, rather than after.

One minor correction - FIFOREADY is a single bit of the register read. Don't interpret reserved bits.

Fixes #7373

Pull request type

[ ] Fix
[X] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

kjbracey · 2018-06-29T09:46:27Z

@RobMeades - something for you to test. I don't have any ITM boards handy.

kjbracey · 2018-06-29T10:01:42Z

Revised a couple of times - now compiles, at least.

RobMeades · 2018-06-29T10:11:22Z

Sweet. Performing printf("Hello world %d.\n", x); in a loop now produces the following output in JLink SWO Viewer and in GDB's SWO console:

Hello world 0.
Hello world 1.
Hello world 2.
Hello world 3.
Hello world 4.

kjbracey · 2018-06-29T10:16:29Z

I'd be interested to see if you could actually measure a performance boost. Or is the port so fast it doesn't really matter?

It may be that it's not really worth the extra code size of doing the 32-bit writes for the block operation.

kjbracey · 2018-06-29T10:20:22Z

Fixed doxygen - no functional change.

…RMmbed/mbed-os#7371 so that SWD output works _really_ sweetly.

kjbracey · 2018-06-29T10:29:03Z

On efficiency, it's possible the C library doesn't end up doing anything more than single-character write() calls anyway. I believe IAR's C library can't be persuaded to do otherwise, and the other libraries may default to non-buffered and need to be explicitly switched to line- or fully-buffered.

You could perhaps test theoretical throughtput more directly with some manual write(STDOUT_FILENO).

RobMeades · 2018-06-29T10:42:02Z

For pure printf() output it appears to work quite fast enough: it didn't really work at all in any of the clients available to me before so I can't easily see what the performance improvement might be. If I sit in a tight loop printf()ing 10 characters at a time I notice no loss in GDB and lines go past way faster than I can read; at a very rough estimate 150 kbytes/s.

marcuschangarm

Looks great!

cmonr

Excited for the changes!

cmonr · 2018-06-30T01:25:56Z

/morph build

cmonr · 2018-06-30T01:27:29Z

@ARMmbed/mbed-os-maintainers Heads up that this PR adds a new function to HAL.
However, I've marked this as for a patch because 1) this is fixing behavior that should be working, and 2) the API addition does not regress user functionality.

mbed-ci · 2018-06-30T04:40:18Z

Build : SUCCESS

Build number : 2486
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7371/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

mbed-ci · 2018-06-30T06:39:47Z

Exporter Build : SUCCESS

Build number : 2125
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7371/

mbed-ci · 2018-06-30T10:03:56Z

Test : SUCCESS

Build number : 2261
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7371/2261

kjbracey · 2018-07-02T09:46:13Z

Sorry - need to correct this. The last commit ca45797 I added was wrong - we do still need the "enabled" checks.

Rereading documentation indicates that writing to the stimulus register is safe when disabled, but we will be getting "not ready" indications when we read, causing us to block indefinitely if disabled.

Removed that commit, leaving just the commit @RobMeades tested.

0xc0170 · 2018-07-02T11:41:04Z

/morph build

mbed-ci · 2018-07-02T13:05:52Z

Build : SUCCESS

Build number : 2494
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7371/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

mbed-ci · 2018-07-02T15:53:42Z

Exporter Build : SUCCESS

Build number : 2138
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7371/

mbed-ci · 2018-07-02T16:03:48Z

Test : SUCCESS

Build number : 2270
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7371/2270

cmonr · 2018-07-03T00:42:30Z

Rebase is needed.

cmonr · 2018-07-03T15:28:07Z

hal/mbed_itm_api.c

+    /* Check if ITM and port is enabled */
+    if (((ITM->TCR & ITM_TCR_ITMENA_Msk) != 0UL) &&      /* ITM enabled */
+            ((ITM->TER & (1UL << port)) != 0UL)) {       /* ITM Port enabled */
+    {


Extra curly brace.

SerialWireOutput was outputting 1 character per 32-bit write to the ITM stimulus port. This is inefficient, and causes processing problems with some viewers due to them receiving 3 NUL bytes between each desired character. Rework to allow us to be more efficient, and eliminate those NUL bytes: * Retain existing mbed_itm_send() and clarify it's a single 32-bit write. * Add new mbed_itm_send_block() that is appropriate for sending character data, and modify SerialWireOutput to use it. * Move "wait for FIFO ready" check to before the write, rather than after. One minor correction - FIFOREADY is a single bit of the register read. Don't interpret reserved bits.

kjbracey · 2018-07-05T12:12:58Z

/morph build

mbed-ci · 2018-07-05T13:05:00Z

Build : SUCCESS

Build number : 2532
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7371/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

mbed-ci · 2018-07-05T14:34:08Z

Test : SUCCESS

Build number : 2294
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7371/2294

mbed-ci · 2018-07-05T14:37:59Z

Exporter Build : SUCCESS

Build number : 2180
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7371/

kjbracey force-pushed the itm_block branch 2 times, most recently from b88cbca to 0129895 Compare June 29, 2018 09:58

RobMeades mentioned this pull request Jun 29, 2018

NULLs in SWO output #7373

Closed

kjbracey force-pushed the itm_block branch from 0129895 to 6d04224 Compare June 29, 2018 10:02

kjbracey force-pushed the itm_block branch from 6d04224 to acdcf42 Compare June 29, 2018 10:19

RobMeades added a commit to u-blox/infinite-iot that referenced this pull request Jun 29, 2018

Update mbed-os and, in fact, for the moment add Kevin Bracey's patch A…

890e560

…RMmbed/mbed-os#7371 so that SWD output works _really_ sweetly.

0xc0170 added the needs: review label Jun 29, 2018

0xc0170 requested a review from marcuschangarm June 29, 2018 10:44

kjbracey force-pushed the itm_block branch from f71b85f to ca45797 Compare June 29, 2018 14:27

marcuschangarm previously approved these changes Jun 29, 2018

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cmonr previously approved these changes Jun 30, 2018

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cmonr added needs: CI release-version: 5.9.3 and removed needs: review labels Jun 30, 2018

cmonr added ready for merge and removed needs: CI labels Jun 30, 2018

kjbracey dismissed cmonr’s stale review via acdcf42 July 2, 2018 09:46

kjbracey dismissed marcuschangarm’s stale review via acdcf42 July 2, 2018 09:46

kjbracey force-pushed the itm_block branch from ca45797 to acdcf42 Compare July 2, 2018 09:46

kjbracey added needs: CI and removed ready for merge labels Jul 2, 2018

cmonr added needs: work and removed needs: CI labels Jul 3, 2018

kjbracey force-pushed the itm_block branch from acdcf42 to 32141f7 Compare July 3, 2018 13:44

cmonr approved these changes Jul 3, 2018

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cmonr suggested changes Jul 3, 2018

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kjbracey force-pushed the itm_block branch from 32141f7 to 0f98338 Compare July 4, 2018 07:16

kjbracey added needs: CI and removed needs: work labels Jul 5, 2018

cmonr approved these changes Jul 5, 2018

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cmonr merged commit c72da66 into ARMmbed:master Jul 5, 2018

cmonr removed the needs: CI label Jul 5, 2018

kjbracey deleted the itm_block branch July 6, 2018 07:53

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Improve efficiency and formatting of ITM output #7371

Improve efficiency and formatting of ITM output #7371

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Improve efficiency and formatting of ITM output #7371

Improve efficiency and formatting of ITM output #7371

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