3.6.2.4.3 ENABLE_AUTOMATIC_MEMORY_LATENCY_SETTING
(Ask a Question)Enable determining memory latency for reads automatically according to the target clock period and timing model of the board. Memory latency is set to 2 when the target clock period is less than the delay of memory for the target device, otherwise is set to 1. Increasing the memory latency can result in higher circuit Fmax at the expense of higher circuit latency. The auto-determined latency can be found in the Memory Usage section of SmartHLS™ report.
Setting the operation latency for a RAM will override the latency automatically calculated. See set_operation_latency for a list of valid memory port latency. The threshold for switching are listed in the table below.
| Device | Use Memory Latency of 2 when Target Period is less than (ns) |
|---|---|
| PolarFire, PolarFire SoC | 4.167 |
| IGLOO2, SmartFusion2 | 4.167 |
| PolarFire 2 | 4.167 |
ENABLE_AUTOMATIC_MEMORY_LATENCY_SETTING controls the latency for the following memory constraints. Each constraint can be used with set_operation_latency <Name> <latency> to override the auto-determined latency.
| Name | Description |
|---|---|
local_memory_port | Controls the memory latency of Local Memory used by a single function. |
shared_local_memory_port | Controls the memory latency of Shared-Local Memory shared by multiple functions. |
axi_slave_ram_memory_port | Controls the memory latency of Legacy AXI4 Slave Interface |
memory_port | Controls the memory latency of Memory Controller |
SmartHLS does not automatically determine the latency for external_memory_port as it is only for creating an interface with the RAMs outside of the circuit. However, for SmartHLS SoC Flow, external_memory_port controls the latency for the on-chip memory buffers.
- Category
- HLS Constraints
- Value Type
- Boolean
- Valid Values
- 0, 1
- Default Value
- 1
- Location Where Default is Specified
examples/legup.tcl- Dependencies
- None
- Applicable Flows
- All devices and flows
- Test Status
- Actively in-use
- Examples
set_parameter ENABLE_AUTOMATIC_MEMORY_LATENCY_SETTING 1