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VCML Models: OpenCores Framebuffer Controller

This is a TLM model of the OpenCores Framebuffer Controller. It supports video output up to 1920x1200 using 32/24/16/8 bit per pixel as well as 8 bit pseudo color using its iternal palette memory. If VCML has been compiled with VNC support, you can connect to the model using a VNC client to display the contents of the video memory.

Properties

This model has the following properties:

Property Type Default Description
vncport u16 0 VNC server port
clock hz_t 60 Screen refresh rate
read_latency sc_time 0ns Extra read delay
write_latency sc_time 0ns Extra write delay
backends string <empty> Ignored
allow_dmi bool true Access VRAM using DMI
loglvl log_level info Logging threshold
trace_errors bool false Report TLM errors

The properties loglvl and trace_errors require loggers.

The vncport property is only used if VCML has been build with VNC support.

Commands

The model supports the following commands during simulation:

Command Description
clist Lists available commands
cinfo <cmd> Shows information about command cmd
reset Resets the component
abort Aborts the simulation
info Prints internal model state

In order to execute commands, an active VSP session is required. Tools such as viper can be used as a graphical frontend for running commands via VSP.

Hardware Interface

The following ports and sockets must be connected prior to simulating:

Port Type Description
IN tlm_target_socket<> Slave bus port
OUT tlm_initiator_socket<> Master bus port
IRQ sc_out<bool> Interrupt port

Software Interface

The model exposes the following memory mapped registers:

Name Offset Access Width Description
CTLR +0x00 R/W 32bit Framebuffer Control Register
STAT +0x04 R 32bit Framebuffer Status Register
HTIM +0x08 R/W 32bit Horizontal Timing Register
VTIM +0x0C R/W 32bit Vertical Timing Register
HVLEN +0x10 R/W 32bit Horizontal & Vertical Length Register
VBARA +0x14 R/W 32bit Video Memory Base Address Register

Additionally, there is a small memory for storing palette colors:

Name Start End Description
CLUT0 +0x800 +0xBFF 256 * 4 bytes for pseudocolor lookup
CLUT1 +0xC00 +0xFFF 256 * 4 bytes for pseudocolor lookup (alt)

The device driver for Linux can be found at:

drivers/video/fbdev/ocfb.c

Driver support in the kernel is controlled via CONFIG_FB_OPENCORES. Set this to y or m to include the driver into the kernel or build it as a module, respectively.

Once this is done, a new device tree node must be added. The following example adds an OpenCores Framebuffer Controller to address 0x93000000:

framebuffer@93000000 {
    compatible = "opencores,ocfb";
    reg = <0x93000000 0x2000>;
    big-endian;
};

Finally, a video mode must be specified on the kernel command line. This can also be done via the device tree within the chosen node:

chosen {
    bootargs = "video=ocfb:1024x768-32@60";
};

For formatting instructions as well as a list of supported video modes, please check the file drivers/video/fbdev/core/modedb.c.

Documentation updated Deccember 2018