Asynchronous Mode; Traceclkin Connection; Tpiu Registers; Table 247. Important Tpiu Registers - ST STM32F423 Reference Manual

Debug support (DBG)
34.17.7

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 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%.
34.17.8

TRACECLKIN connection

The 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 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.
34.17.9

TPIU registers

The TPIU APB registers can be read and written only if the bit TRCENA of the Debug
Exception and Monitor Control Register (DEMCR) is set. Otherwise, the registers are read
as zero (the output of this bit enables the PCLK of the TPIU).
Address
0xE0040004 Current port size
Selected pin
0xE00400F0
protocol
1312/1324

Table 247. Important TPIU registers

Register
Allows the trace port size to be selected:
Bit 0: Port size = 1
Bit 1: Port size = 2
Bit 2: Port size = 3, not supported
Bit 3: Port Size = 4
Only 1 bit must be set. By default, the port size is one bit. (0x00000001)
Allows the Trace Port Protocol to be selected:
Bit1:0=
00: Sync Trace Port Mode
01: Serial Wire Output - manchester (default value)
10: Serial Wire Output - NRZ
11: reserved
Description
RM0430 Rev 8
RM0430