Embedded Peripherals IP User Guide

ID 683130
Date 10/24/2025
Public
Document Table of Contents
1. Introduction 2. Avalon® -ST Serial Peripheral Interface Core 3. SPI Core 4. SPI Agent/JTAG to Avalon® Host Bridge Cores 5. Intel eSPI Agent Core 6. eSPI to LPC Bridge Core 7. Ethernet MDIO Core 8. Intel FPGA 16550 Compatible UART Core 9. UART Core 10. Lightweight UART Core 11. JTAG UART Core 12. Intel FPGA Avalon® Mailbox Core 13. Intel FPGA Avalon® Mutex Core 14. Intel FPGA Avalon® I2C (Host) Core 15. Intel FPGA I2C Agent to Avalon® -MM Host Bridge Core 16. EPCS/EPCQA Serial Flash Controller Core 17. Intel FPGA Serial Flash Controller Core 18. Intel FPGA Serial Flash Controller II Core 19. Intel FPGA Generic QUAD SPI Controller Core 20. Intel FPGA Generic QUAD SPI Controller II Core 21. Interval Timer Core 22. Intel FPGA Avalon FIFO Memory Core 23. On-Chip Memory (RAM and ROM) Intel FPGA IP 24. On-Chip Memory II (RAM or ROM) Intel FPGA IP 25. PIO Core 26. PLL Cores 27. DMA Controller Core 28. Modular Scatter-Gather DMA Core 29. Scatter-Gather DMA Controller Core 30. Video Sync Generator and Pixel Converter Cores 31. Intel FPGA Interrupt Latency Counter Core 32. Performance Counter Unit Core 33. Vectored Interrupt Controller Core 34. System ID Peripheral Core 35. Intel FPGA GMII to RGMII Converter Core 36. HPS GMII to RGMII Adapter IP 37. Intel FPGA MII to RMII Converter Core 38. HPS GMII to TSE 1000BASE-X/SGMII PCS Bridge Core IP 39. Intel FPGA HPS EMAC to Multi-rate PHY GMII Adapter Core 40. Intel FPGA MSI to GIC Generator Core 41. Cache Coherency Translator IP 42. Altera ACE5-Lite Cache Coherency Translator

33.8.1.4. Funnel Latency

Funnel latency is the time required for the interrupt funnel to switch context. Funnel latency can include saving and restoring registers, managing preemption, and managing the stack pointer. Funnel latency depends on the following factors:

  • Whether a separate interrupt stack is used
  • The number of clock cycles required for load and store instructions
  • Whether the interrupt requires switching to a different register set
  • Whether the interrupt is preempting another interrupt within the same register set
  • Whether preemption within the register set is allowed

Preemption within the register set requires special attention. The HAL VIC driver provides special funnel code if an interrupt is allowed to preempt another interrupt assigned to the same register set. In this case, the funnel incurs additional overhead to save and restore the register contents. When creating the BSP, you can control preemption within the register set by using the VIC driver’s altera_vic_driver_enable_preemption_rs_<n> setting.

Note: With tightly-coupled memory, the Nios® II processor can execute a load or store instruction in 1 clock cycle. With onchip memory, not tightly-coupled, the processor requires two clock cycles.
Table 506.  Single Stack HAL latency
Funnel Type Clock Cycles Required for Load or Store
  1 2
Shadow register set, preemption within the register set disabled 10 13
Shadow register set, preemption within the register set enabled 42

Same register set (sstatus.SRS=0)

64

Same register set (sstatus.SRS=0)

26

Different register set (sstatus.SRS=1)

32

Different register set (sstatus.SRS=1)

Table 507.  Separate Interrupt Stack HAL Latency
Funnel Type Clock Cycles Required for Load or Store
  1 2
Shadow register set, preemption within the register set disabled 11

Not preempting another interrupt (sstatus.IH=0)

14

Not preempting another interrupt (sstatus.IH=0)

12

Preempting another interrupt (sstatus.IH=1)

15

Preempting another interrupt (sstatus.IH=1)

Shadow register set, preemption within the register set enabled 42

Same register set (sstatus.SRS=0)

64

Same register set (sstatus.SRS=0)

27
  • Different register set (sstatus.SRS=1)
  • Not preempting another interrupt (sstatus.IH=0)
33
  • Different register set (sstatus.SRS=1)
  • Not preempting another interrupt (sstatus.IH=0)
28
  • Different register set (sstatus.SRS=1)
  • Preempting another interrupt (sstatus.IH=1)
34
  • Different register set (sstatus.SRS=1)
  • Preempting another interrupt (sstatus.IH=1)

In the tables above, notice that the lowest latencies occur under the following conditions:

  • A different register set—Shadow register set switch; the ISR runs in a different register set from the interrupted task, eliminating any need to save or restore registers.
  • Preemption (nesting) within the register set disabled.

Conversely, the highest latencies occur under the following conditions:

  • The same register set—No shadow register set switch; the ISR runs in the same register set as the interrupted task, requiring the funnel code to save and restore registers.
  • Preemption within the register set enabled.

Of these two important factors, preemption makes the largest difference in latencies. With preemption disabled, much lower latencies occur regardless of other factors.