A simple design with Wishbone bus

2008-11-06T09:03:44Z

CamilleD: URL of the example sourceforge link corrected : 'wishbone_example' instead of 'Wisbone_example'

[[Category: FPGA]]
This article intended to explain how to design Wishbone compatible
components with simple example.
The VHDL design can be found in sourceforge
[http://armadeus.svn.sourceforge.net/viewvc/armadeus/trunk/firmware/wishbone_example/ tree].

Description of wishbone structure for armadeus can be found [[FpgaArchitecture#Le_bus_Wishbone | here]] in french.

== General structure ==

The main functionality of this component is to do the same things
that [[FPGA_and_led | benoît]] project : switch on a led when a button is
pressed.

But to learn about designing Wishbone component and linux driver, the design
is little bit more complicated (!).

When button is pressed, the component ''Wb_button'' send interrupt signal to ''irq_mngr''. ''irq_mngr'' will toggle a flag and send interruption to
'''i.mx''' processor. A Linux driver on '''i.mx''' will read ''irq_mngr'' and
acknowledge irq by writing '1' on a register. And finally, Linux driver will
toggle led value by writing on led register.

[[Image:Wb_buttonled_top.png|center|800px]]

''imx_wrapper'', ''syscon'' and ''irq_mngr'' are standards
ARMadeus-Wishbone IPs that just been instantiated in our design.

''Wb_button'' and ''Wb_led'' are simple slave component we want to
integrate in the FPGA.

All these components are connected together with the 'glue logic' component ''intercon''.

== Wishbone slave application components ==

=== Wb_led ===

This component is a simple 16-bit Wishbone slave output port, from [http://www.opencores.org/projects.cgi/web/wishbone/wbspec_b3.pdf wishbone specification example] (p110).

[[Image:wbs_led.png|center|600px]]

It is a simple register, that can be read and write. The led is controled with register pin 0.

[[Wb_led.vhd | The VHDL source code]]

=== Wb_button ===

Wb_button component, is like Wb_led but in read only and with an edge detector to rise irq.

[[Image:wbs_button.png|center|500px]]

[[Wb_button.vhd | The VHDL source c]]ode

== Drivers ==

=== Wb_led ===
The Wb_led driver implements a character device with read(), write() system calls. It implements sys/led/status entry. Driver sources can be found in [http://armadeus.svn.sourceforge.net/viewvc/armadeus/trunk/target/linux/modules/fpga/others/Wb_led/ sourceforge].

=== Wb_button ===
The Wb_button driver implements a character device with only read() system calls. If used as blocking read, it will return value only when button is push/release. Drivers sources are on [http://armadeus.svn.sourceforge.net/viewvc/armadeus/trunk/target/linux/modules/fpga/others/Wb_button/ sourceforge].

== XML ==

ArmadeusWiki - User contributions [en]

A simple design with Wishbone bus