In this mode, a 32-bit counter is used to generate a fixed length measurement window. When the counter reaches the maximum value, it resets to a value specified in the VCU_SLCR.APMn_TIMER (n = 0, 1, 2, 3) register. The measurement is continued until the 32-bit counter reaches the value set in the APMn_TIMER register and a capture pulse is generated to store the measured values in the VCU_SLCR result registers.
The VAPM is capable of doing the following measurements:
- AXI Read and Write Transaction Measurement
- Two 32-bit registers count number of read and write 128-bit AXI bus cycles transferred in a given timing window. The measured value is transferred to the VCU_SLCR result register when a capture pulse is generated based on the start/stop mode or the fixed duration timing window mode. To compute the number of bytes transferred, VCU_SLCR must be multiplied by 16.
- AXI Read and Write Byte Count Measurement
- Two 32-bit registers are implemented to count number of read and write bytes transferred in a given timing window. The register content has to be multiplied by 16 to know the actual byte count transferred across AXI 128-bit master interface. The measured value is transferred to the VCU_SLCR result register when a capture pulse is generated based on the start/stop mode or fixed duration timing window mode.
- AXI Transaction Latency Measurement
- Read and write latency can be measured based on AXI master ID. Read latency is defined as AXI read address acknowledged to last read data cycle. Write latency is defined as AXI write address acknowledged to write response handshaking between master and slave. A 13-bit counter is implemented to measure the latency on read and write bus. The timer is used to timestamp an event. The difference in the timestamp between two events is used to calculate the latency.
Latency can be calculated on transaction ID basis. It is possible to select a single ID or all IDs for latency calculation. For additional information, see the Zynq UltraScale+ Device Register Reference (UG1087).