SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
The CS_STM embedded in the MPU subsystem provides extended stimulus port registers designated to be accessible by software with minimum instrumentation cycles overhead.
Each extended stimulus port occupies 256 consecutive bytes in the memory map and is write-only. Up to 64K instrumentation channels are available at MPU level.
The CS_STM supports "guaranteed" or invariant timing transactions:
The CS_STM implements tracing of software writes to its stimulus ports using a dedicated AXI slave interface. In addition to the AXI interface, the CS_STM provides a hardware event input interface (HWEVENTS[31:0]). The HWEVENTS[31:0] input bus is connected to the MPU hardware debug observability signals going out to the MPU hardware debug port (MPUHWDBGOUT[31:0]). This enables any of the signals observed on MPUHWDBGOUT[31:0] to act as a hardware event to the CS_STM. The CS_STM can be programmed to generate a debug packet on a rising edge transition on any signal of the HWVENTS[31:0] input bus. Because some of the signals mapped on the MPUHWDBGOUT[31:0] bus are active low, a 32-bit programmable register – MPU.STM_HWEVENTS_INV, is implemented for polarity inversion. Each bit of MPU.STM_HWEVENTS_INV when set to 0x1 inverts the polarity of the corresponding signal of MPUHWDBGOUT[31:0] going to HWEVENTS[31:0]. This programmable register is part of the MPU_WUGEN address map (see Chapter 4, Dual Cortex-A15 MPU Subsystem, for its description).
The MPUHWDBGOUT[31:0] signals can be routed to the hw_dbg[31:0] device pads through various hardware debug observability MUXes controlled by device control module (CTRL_MODULE). For more information, see Chapter 18, Control Module.
To save power, the output port can be gated off (to all zeros) by setting the CTRL_MODULE. CONTROL_HWOBS_CONTROL[0] HWOBS_MACRO_ENABLE bit to 0x0. Ungated version of MPUHWDBGOUT[31:0] (not gated with CTRL_MODULE. CONTROL_HWOBS_CONTROL[0] HWOBS_MACRO_ENABLE) is sent to HWEVENTS[31:0] input of STM so each of these signals can generate a debug packet on the trace port.
The message structures in STP-2.0 are optimized to provide an efficient transport.