tcam

TCAM (Ternary Content-Addressable Memory) in Verilog.

Specifications

• Index table implemented on distributed memory (registers)
• Data table implemented on Simple Dual Port Memory (distributed or block)
• Set/Clear latency: 1
• Request latency: 3

Parameters:

• ADDR_WIDTH - Address width
• KEY_WIDTH - Key and Mask width
• DATA_WIDTH - Data width
• MASK_DISABLE - Disable mask flag
• RAM_STYLE_DATA - ram_style attribute for data memory

Ports

• clk - Input clock
• rst - Synchronous reset (active-HIGH)
• set_addr - Input Address for Set/Clear operation
• set_data - Input Data for Set operation
• set_key - Input Key for Set operation
• set_xmask - Input Mask for Set operation
• set_clr - Input Clear flag for Set/Clear operation
• set_valid - Input Valid flag for Set/Clear operation
• req_key - Input Key for Request operation
• req_valid - Input Valid flag for Request operation
• req_ready - Output Ready flag for Request operation
• res_addr - Output Address for Request operation
• res_data - Output Data for Request operation
• res_valid - Output Valid flag for Request operation
• res_null - Output Null flag for Request operation ('not found')

Example Timings

Example timing diagram contains 4 stages:

• Set stage: fills TCAM with data and masks
• Success request stage: requests data by key
• Clear stage: clears data with address <0x1>
• Failed request stage: no correct data in TCAM (res_null signal is ACTIVE)

Structure

Top

Description:

• line_array - array of lines, each line contains registered memory (keys and masks) and matching logic
• line_encoder - converts input line match signals to corresponding addresses sequentially
• ram - random access memory containing data

Line

Description:

Each key and mask are contained in the registered memory. This circumstance allows implement parallel matching logic. The output match signal is comparison of zero with results of function: "buffered key" XOR "input request key" AND "inverted buffered mask".