[Oberon] FPGA Oberon - Reset Button

thomas.kral at email.cz thomas.kral at email.cz
Thu Mar 23 10:56:31 CET 2017

Hi Magnus, Hi Paul,

Yes, now I see, I am sorry for asking when it should be obvious from the 
verilog source.

I am studying the code, while trying to get myself on a free verilog course 
for beginners.

BTW, are there some of the original machines, Lilith, Ceres still preserved 
at ETH? 


---------- Původní zpráva ----------
Od: Magnus Karlsson <magnus at saanlima.com>
Komu: paulreed at paddedcell.com, ETH Oberon and related systems <oberon at lists.
Datum: 23. 3. 2017 0:37:10
Předmět: Re: [Oberon] FPGA Oberon - Reset Button

"On 3/22/2017 12:43 PM, Paul Reed wrote: 
> Hi Tomas, 
>> I wish to install reset switch, which pin header / button is the reset? 
> ... 
>> Connector J8 
>> 3.3V GND BTN0 BTN1 BTN2 BTN3 N/C N/C N/C N/C 
> On the Spartan 3 board btn3 is marked "User Reset" but since you have (I 
> believe) a Pepino you wouldn't necessarily know that. :) 
> The relevant line in Prof. Wirth's Verilog is in RISC5Top.v, near the 
> ... 
> always @(posedge clk) 
> begin 
> rst <= ((cnt1[4:0] == 0) & limit) ? ~btn[3] : rst; 
> ... 

On Pepino, the pusbutton signal is OR'd with btn[3], like this: 

always @(posedge clk) 
rst <= ((cnt1[4:0] == 0) & limit) ? ~(btn[3] | button) : rst; 

So you can either use the BTN3 signal available in the I/O header or the 
pushbutton to do the reset. 

> Note that this reset merely aborts the current Oberon command and returns 
> to the main loop, like the Interrupt key on the Ceres. 
> There isn't an I/O signal which does a cold reset of the Oberon system in 
> the way a PC reset button works, since the Spartan 3 board has a 
> pushbutton called "Prog" which reloads the FPGA configuration (forcing a 
> complete cold start of the hardware). 
> >From the Pepino schematic it looks like Magnus has the Spartan 6 FPGA 
> pin just pulled high (signal PROGRAM_B) by resistor R32. You could try 
> grounding the other side of the resistor to get the same effect as the 
> PROG button - but take care not to destroy your board obviously! 

Or just power-cycle the board, it has the same effect. 

> There is a pushbutton on the Pepino, marked "BUTTON" on the schematic, but

> you'd have to change the Verilog and reprogram the board if you wanted to 
> use that as btn3. 

See above, the pushbutton is OR'd with the btn3 signal from the I/O 

It would be a minor change to the Verilog code to make it reload the 
instead of aborting the current command. 

> HTH 
> Paul 
Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems 
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