framebuffer_teletext

Files
file	framebuffer_teletext.cdl
	Teletext framebuffer module with separate write and video sides.

Detailed Description

Modules

module framebuffer_teletext::framebuffer_teletext	(	clock	csr_clk,
		clock	sram_clk,
		clock	video_clk,
		input bit	reset_n,
		input t_bbc_display_sram_write	display_sram_write,
		output t_video_bus	video_bus,
		input bit	csr_select_in[16],
		input t_csr_request	csr_request,
		output t_csr_response	csr_response
	)

Parameters

[in]	csr_clk	Clock for CSR reads/writes
[in]	sram_clk	SRAM write clock, with frame buffer data
[in]	video_clk	Video clock, used to generate vsync, hsync, data out, etc
[out]	csr_response	This module provides a teletext framebuffer of configurable size.

Each character is 12x10 pixels - horizontally smoothed, but not vertically.

This module incorporates a framebuffer_timing module which should be configured with the correct display size and porches; the csr_select used for this is 1 more than that used for this module itself.

The module includes a CSR target with two registers: framebuffer start address (register 0), and SRAM words per line (register 1). The words-per-line register should be initialized to the number of characters in a line (i.e. displayed pixels/12). The framebuffer start register can be used to have multiple framebuffers, or to provide for scrolling, or it can be held at 0.