Debug support (DBG) RM0008
1076/1096 Doc ID 13902 Rev 12
31.17.7 Asynchronous mode
This is a low cost alternative to output the trace using only 1 pin: this is the asynchronous
output pin TRACESWO. Obviously there is a limited bandwidth.
TRACESWO is multiplexed with JTDO when using the SW-DP pin. This way, this
functionality is available in all STM32F10xxx packages.
This asynchronous mode requires a constant frequency for TRACECLKIN. For the standard
UART (NRZ) capture mechanism, 5% accuracy is needed. The Manchester encoded
version is tolerant up to 10%.
31.17.8 TRACECLKIN connection inside the STM32F10xxx
In the STM32F10xxx, this TRACECLKIN input is internally connected to HCLK. This means
that when in asynchronous trace mode, the application is restricted to use to time frames
where the CPU frequency is stable.
Note: Important: when using asynchronous trace: it is important to be aware that:
The default clock of the STM32F10xxx MCUs is the internal RC oscillator. Its frequency
under reset is different from the one after reset release. This is because the RC calibration is
the default one under system reset and is updated at each system reset release.
Consequently, the trace port analyzer (TPA) should not enable the trace (with the
TRACE_IOEN bit) under system reset, because a Synchronization Frame Packet will be
issued with a different bit time than trace packets which will be transmitted after reset
release.
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