S_AXILITE Control Register Map - 2022.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
Release Date
2022.2 English
Vitis HLS automatically generates a Control Register Map for controlling the Vivado IP or Vitis kernel, and the ports grouped into s_axilite interface. The register map, which is added to the generated RTL files, can be divided into two sections:
  1. Block-level control signals
  2. Function arguments mapped into the s_axilite interface
In the Vitis kernel flow, the block protocol is associated with the s_axilite interface by default. To change the default block protocol, specify the interface pragma as follows:
#pragma HLS INTERFACE mode=ap_ctrl_hs port=return
In the Vivado IP flow though, the block control protocol is assigned to its own interface, ap_ctrl, as seen in Interfaces for Vivado IP Flow. However, if you are using an s_axilite interface in your IP, you can also assign the block control protocol to that interface using the following INTERFACE pragmas, as an example:
#pragma HLS INTERFACE mode=s_axilite port=return bundle=BUS_A
#pragma HLS INTERFACE mode=ap_ctrl_hs port=return bundle=BUS_A

In the Control Register Map, Vitis HLS reserves addresses 0x00 through 0x18 for the block-level protocol, interrupt, mailbox and auto-restart controls. The latter are present only when counted auto-restart and the mailbox are enabled, as shown below:

Table 1. Addresses
Address Description
0x00 Control signals
0x04 Global Interrupt Enable Register
0x08 IP Interrupt Enable Register (Read/Write)
0x0c IP Interrupt Status Register (Read/TOW)
0x10 Auto-restart counter (Write; present only with counted autorestart)
0x14 Input mailbox write (Read/Write; present only when the input mailbox is enabled)
0x18 Output mailbox read (Read/Write; present only when the output mailbox is enabled)

The Control signals (0X00) contains ap_start, ap_done, ap_ready, and ap_idle; and in the case of ap_ctrl_chain the block protocol also contains ap_continue. These are the block-level interface signals which are accessed through the s_axilite adapter.

To start the block operation theap_start bit in the Control register must be set to 1. The HLS engine will then proceed and read any inputs grouped into the AXI4-Lite slave interface from the register in the interface.

When the block completes the operation, theap_done,ap_idleandap_ready registers will be set by the hardware output ports and the results for any output ports grouped into the s_axilite interface read from the appropriate register.

For function arguments, Vitis HLS automatically assigns the address for each argument or port that is assigned to the s_axilite interface. The tool will assign each port an offset starting from 0x10, the lower addresses being reserved for control signals. The size, or range of addresses assigned to a port is dependent on the argument data type and the port protocol used.

Because the variables grouped into an AXI4-Lite interface are function arguments which do not have a default value in the C code, none of the argument registers in the s_axilite interface can be assigned a default value. The registers can be implemented with a reset using the config_rtl command, but they cannot be assigned any other default value.

The Control Register Map generated by Vitis HLS is provided below:

//------------------------Address Info-------------------
// 0x00 : Control signals
//        bit 0  - ap_start (Read/Write/COH)
//        bit 1  - ap_done (Read)
//        bit 2  - ap_idle (Read) can be disabled with config_rtl -no_idle
//        bit 3  - ap_ready (Read/COR)
//        bit 4  - ap_continue (Read/Write/SC) for ap_ctrl_chain protocol
//        bit 7  - auto_restart (Read/Write) enabled by config_interface -s_axilite_auto_restart_counter  
//        bit 9  - interrupt (Read) Present when there is at least one enabled interrupt 
//        others - reserved
// 0x04 : Global Interrupt Enable Register
//        bit 0  - Global Interrupt Enable (Read/Write)
//        others - reserved
// 0x08 : IP Interrupt Enable Register (Read/Write)
//        bit 0  - enable ap_done interrupt (Read/Write)
//        bit 1  - enable ap_ready interrupt (Read/Write)
//        others - reserved
// 0x0c : IP Interrupt Status Register (Read/TOW)
//        bit 0  - ap_done (COR/TOW)
//        bit 1  - ap_ready (COR/TOW)
//        others - reserved
// 0x10 : Data signal of a
//        bit 7~0 - a[7:0] (Read/Write)
//        others  - reserved
// 0x14 : reserved
// 0x18 : Data signal of b
//        bit 7~0 - b[7:0] (Read/Write)
//        others  - reserved
//  : Control signal of b
//        bit 0  - b_ap_vld (Read/Write/SC)
//        others - reserved
// 0x20 : Data signal of c_i
//        bit 7~0 - c_i[7:0] (Read/Write)
//        others  - reserved
// 0x24 : reserved
// 0x28 : Data signal of c_o
//        bit 7~0 - c_o[7:0] (Read)
//        others  - reserved
// 0x2c : Control signal of c_o
//        bit 0  - c_o_ap_vld (Read/COR)
//        others - reserved
// (SC = Self Clear, COR = Clear on Read, TOW = Toggle on Write, COH = Clear on Handshake)