ST STM32F301 6 Series Reference Manual page 860

Debug support (DBG)
28.15.8 TPUI frame synchronization packets
The TPUI can generate two types of synchronization packets:
•
The Frame Synchronization packet (or Full Word Synchronization packet)
It consists of the word: 0x7F_FF_FF_FF (LSB emitted first). This sequence cannot
occur at any other time provided that the ID source code 0x7F has not been used.
It is output periodically between frames.
In continuous mode, the TPA must discard all these frames once a synchronization
frame has been found.
•
The Half-Word Synchronization packet
It consists of the half word: 0x7F_FF (LSB emitted first).
It is output periodically between or within frames.
These packets are only generated in continuous mode and enable the TPA to detect
that the TRACE port is in IDLE mode (no TRACE to be captured). When detected by
the TPA, it must be discarded.
28.15.9 Transmission of the synchronization frame packet
There is no Synchronization Counter register implemented in the TPIU of the core.
Consequently, the synchronization trigger can only be generated by the DWT. Refer to the
registers DWT Control Register (bits SYNCTAP[11:10]) and the DWT Current PC Sampler
Cycle Count Register.
The TPUI Frame synchronization packet (0x7F_FF_FF_FF) is emitted:
• after each TPIU reset release. This reset is synchronously released with the rising
edge of the TRACECLKIN clock. This means that this packet is transmitted when the
TRACE_IOEN bit in the DBGMCU_CFG register is set. In this case, the word
0x7F_FF_FF_FF is not followed by any formatted packet.
• at each DWT trigger (assuming DWT has been previously configured). Two cases
occur:
–
–
28.15.10 Synchronous mode
Synchronous mode is not supported.
28.15.11 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 STM32F3xx 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%.
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If the bit SYNENA of the ITM is reset, only the word 0x7F_FF_FF_FF is emitted
without any formatted stream, which follows.
If the bit SYNENA of the ITM is set, then the ITM synchronization packets follow
(0x80_00_00_00_00_00), formatted by the TPUI (trace source ID added).
RM0366 Rev 5
RM0366