The RRD Register characteristics are:
Reading this register enables data to be read from the trace memory. When the memory width given in the DEVID register is greater than 32 bits, multiple reads to this register must be performed together to read a full memory width of data. For example, if the memory width is 128 bits, then reads from this register must be performed four at a time. When a full memory width of data has been read, the RAM Read Pointer is incremented to the next memory word.When no data is available, this register returns
0xFFFFFFFF. This value is chosen because it cannot be generated as part of the trace data when the formatter is enabled. See Standard usage models for the TMC.
- Trace Capture disabled
When in Disabled state, the TMC mode is ignored. Reading this register returns the contents of the Local RAM buffer or AXI memory at the location addressed by the RAM Read Pointer Register.
- Circular Buffer mode
When in Stopped state in Circular Buffer mode and the buffer is not empty, reading this register returns the next word of data from the trace buffer. When all of the trace buffer has been read, the Empty bit in the STS Register is set, and more reads return
0xFFFFFFF.Reading this register when not in Stopped state returns
- Software FIFO mode
Reading this register returns data from the FIFO. If this register is read when the FIFO is empty, the data returned is
- Hardware FIFO mode
Reading this register returns
Reading this register alters the internal state of the TMC, and can only be performed if the device is unlocked. Reading this register when the device is locked returns
In the ETR configuration, when the MemErr bit in the STS Register is set, reading this register returns an error response on the APB slave interface.
Present in all configuration.
Figure 3.3 shows the RRD Register bit assignments.
Table 3.4 shows the RRD Register bit assignments.