Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

5.4.4.1. Boot Time Performance for Design that Boots from On Chip Flash with Flash Accelerator

The following bar graphs show the boot time performance for designs that boot from on-chip flash (application code stored in on-chip flash) with and without the flash accelerator (FA) unit. Three scenarios have been evaluated:

  1. Design with EMIF that runs from external memory DDR3 (using boot copier).
  2. Design without EMIF that runs from on-chip memory (using boot copier).
  3. Design without EMIF that runs from on-chip flash (execute in-place).
Note: None of the designs include an instruction or data cache.
Figure 237. Summary of Boot Times for Designs that Boot from On-Chip Flash with or without Flash Accelerator

The boot time was reduced by ~20% and ~44% for 9 kB and 32 kB application sizes respectively when the Nios® II FA is enabled. Larger application sizes will result in longer boot times because the code has to be copied from the on-chip flash to the external memory during the boot process. Overall, the boot time for the scenario where the boot code is running from the external memory is the slowest. This is due to the long time taken by external memory calibration during system boot up and the time taken to copy the application code to external memory.

Figure 238. Boot Time for Design without EMIF that runs from On-Chip Memory

The boot time was reduced by ~77% and ~76% for 9 kB and 32 kB application sizes respectively when the Nios® II FA is enabled. Running the boot code from the on-chip memory is faster than running from external memory because the on-chip memory does not need to go through memory calibration during system boot up. Additionally, access time to the on-chip memory are faster than those for external DDR3 memory.

Figure 239. Boot Time for Design without EMIF that runs from On-Chip Flash (Execute In-Place)

The boot time was reduced by ~78% and ~77% for 9 kB and 32 kB application sizes respectively when the Nios® II FA is enabled. Running the boot code from the on-chip flash (execute in-place) is faster than running from external memory and on-chip memory. This is because the code executes in-place directly from the on-chip flash and does not need to be copied into the external memory or on-chip memory for execution which saves a lot of time.