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

8.4.10. afr

Identifier Title Offset Access Reset Value Description
afr Additional Features Register 0x100 RW 0x00000000 These registers enable additional features in the soft UART controller. These features are specific to Intel FPGA.
Bit Fields
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
tx_low_en
Table 77.  afr Fields
Bit Name/Identifier Description Access Reset
[31:1] Reserved R 0x0
[0] Transmit FIFO Low Watermark Enable Register (tx_low_en) This bit controls the Tx FIFO Low Watermark feature. This feature requires FIFO to be enabled (FCR[0]). When enabled, the UART will send a Transmit Holding Register Empty status interrupt when the Transmit FIFO level is at or below the value stored in tx_low. Legal values for tx_low can range from zero up to depth of FIFO minus two. UART behavior is undefined when tx_low is set to illegal values.
  • 1 - Transmit FIFO Low Watermark is set by tx_low
  • 0 - Transmit FIFO Low Watermark is unset
This value must only be changed when the Transmit FIFO is empty or before FIFO is enabled (FCR[0]). This register is meant to be changed during UART initialization before active traffic is sent. The Transmit FIFO should be reset using FCR[2] after any changes to this value.
RW 0x0