MTB specifics
The ARM Micro Trace Buffer (MTB) is an on-chip trace buffer that allows to do post-mortem instruction trace via a regular J-Link with no need of a specific J-Trace unit. The MTB will use a specific amount of the on-chip RAM to store trace data while the core executes instructions. MTB is mainly used on smaller MCUs like Cortex-M0+/M23/M33 based ones.
Limitations
MTB is a very limited version of trace that has the following limitations:
- Instruction trace support only
- No streaming trace possible
- A portion of the target RAM may not be used by the application if MTB is used
Configuration options provided by J-Link
An MTB consists of the following registers / bit fields that allow configuration of the MTB and the amount of RAM it uses:
| Register / Bit field | Description |
|---|---|
| MTB_BASE | 32-bit register that specifies the base address of the MTB buffer |
| MTB_POINTER | 32-bit register that specifies the offset (rel. to BASE) where the next trace packet will be stored by the HW |
| MTB_MASTER.MASK | 5-bit bitfield that specifies the wrap-around point for the auto-inc logic of the MTB, on packet store |
While the MTB_BASE register is read-only for J-Link, the MTB_POINTER and MTB_MASTER.MASK can be written by J-Link. This allows the MTB RAM usage to be configured.
