Embedded Peripherals IP User Guide

ID 683130
Date 12/13/2021
Public

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Document Table of Contents
1. Introduction 2. Avalon® -ST Multi-Channel Shared Memory FIFO Core 3. Avalon® -ST Single-Clock and Dual-Clock FIFO Cores 4. Avalon® -ST Serial Peripheral Interface Core 5. SPI Core 6. SPI Agent/JTAG to Avalon® Host Bridge Cores 7. Intel eSPI Agent Core 8. eSPI to LPC Bridge Core 9. Ethernet MDIO Core 10. Intel FPGA 16550 Compatible UART Core 11. UART Core 12. JTAG UART Core 13. Intel FPGA Avalon® Mailbox Core 14. Intel FPGA Avalon® Mutex Core 15. Intel FPGA Avalon® I2C (Host) Core 16. Intel FPGA I2C Agent to Avalon® -MM Host Bridge Core 17. Intel FPGA Avalon® Compact Flash Core 18. EPCS/EPCQA Serial Flash Controller Core 19. Intel FPGA Serial Flash Controller Core 20. Intel FPGA Serial Flash Controller II Core 21. Intel FPGA Generic QUAD SPI Controller Core 22. Intel FPGA Generic QUAD SPI Controller II Core 23. Interval Timer Core 24. Intel FPGA Avalon FIFO Memory Core 25. On-Chip Memory (RAM and ROM) Intel FPGA IP 26. On-Chip Memory II (RAM or ROM) Intel FPGA IP 27. Optrex 16207 LCD Controller Core 28. PIO Core 29. PLL Cores 30. DMA Controller Core 31. Modular Scatter-Gather DMA Core 32. Scatter-Gather DMA Controller Core 33. SDRAM Controller Core 34. Tri-State SDRAM Core 35. Video Sync Generator and Pixel Converter Cores 36. Intel FPGA Interrupt Latency Counter Core 37. Performance Counter Unit Core 38. Vectored Interrupt Controller Core 39. Avalon® -ST Data Pattern Generator and Checker Cores 40. Avalon® -ST Test Pattern Generator and Checker Cores 41. System ID Peripheral Core 42. Avalon® Packets to Transactions Converter Core 43. Avalon® -ST Multiplexer and Demultiplexer Cores 44. Avalon® -ST Bytes to Packets and Packets to Bytes Converter Cores 45. Avalon® -ST Delay Core 46. Avalon® -ST Round Robin Scheduler Core 47. Avalon® -ST Splitter Core 48. Avalon® -MM DDR Memory Half Rate Bridge Core 49. Intel FPGA GMII to RGMII Converter Core 50. Intel FPGA MII to RMII Converter Core 51. Intel FPGA HPS GMII to TSE 1000BASE-X/SGMII PCS Bridge Core 52. Intel FPGA HPS EMAC to Multi-rate PHY GMII Adapter Core 53. Intel FPGA MSI to GIC Generator Core

38.7.4. Positioning the ISR in Vector Table

If have a critical ISR of small size, you can achieve the best performance by positioning the ISR code directly in the vector table. In this way, you eliminate the overhead of branching from the vector table through the HAL funnel to your ISR.This section describes how to modify the VIC Basic example software to create the VIC Table-Resident example. Use this example to ensure that you understand the steps. Then you can make the equivalent changes in your custom code.

Positioning an ISR in a vector table is an advanced and error-prone technique, not directly supported by the HAL. You must exercise great caution to ensure that the ISR code fits in the vector table entry. If your ISR overflows the vector table entry, it corrupts other entries in the vector table, and your entire interrupt handling system.

When locate your ISR in the vector table, it does not need to be registered. Do not call alt_ic_isr_register(), because it overwrites the contents of the vector table.

When the ISR is in the vector table, the HAL does not provide funnel code. Therefore, the ISR code must perform any context-switching actions normally handled by the funnel. Funnel context switching can include some or all of the following actions:

  • Saving and restoring registers
  • Managing preemption
  • Managing the stack pointer

To create the fastest possible ISR, minimize or eliminate the context-switching actions your ISR must perform by conforming to the following guidelines:

  • Write the ISR in assembly language
  • Assign a shadow register set for the ISR’s use
  • Ensure that the ISR cannot be preempted by another ISR using the same register set. By default, preemption within a register set is disabled on the Nios® II processor. You can also ensure this condition by giving the ISR exclusive access to its register set.

The VIC Table-Resident example requires modifying a BSP-generated file, altera_vic1_vector_tbl.S. If you regenerate the BSP after making these modifications, the Nios® II Software Build Tools regenerate altera_vic1_vector_tbl.S, and your changes are overwritten.