Re: [openrisc] is this a bug in or1200's except logic?

["Damjan Lampret" <lampret@opencores.org>]

How did you test this? Did you use SW test case? If yes, can you send it.
Thanks.

regards,
Damjan

----- Original Message -----
From: "qcpassed" <qcpassed@sina.com>
To: <openrisc@opencores.org>
Sent: Thursday, April 10, 2003 8:37 PM
Subject: [openrisc] is this a bug in or1200's except logic?


  I only simulate the or1200_cpu logic with modelsim.
  I found that the exception vector's first instruction will never be
excuted when a exception,trap or syscall happen.
The reason is listed bellow:
  1) first I list the related original codes
file://-----------------in or1200_genpc.v---------------------------
 assign icpu_cycstb_o = !genpc_freeze;
always @(posedge clk or posedge rst)
if (rst)
pcreg <= #1 30'd63;
else if (spr_pc_we)
pcreg <= #1 spr_dat_i[31:2];
else if (no_more_dslot | except_start | !genpc_freeze & !icpu_rty_i &
!genpc_refetch)
// else if (except_start | !genpc_freeze & !icpu_rty_i & !genpc_refetch)
pcreg <= #1 pc[31:2];
file://-----------------in or1200_freeze.v--------------------------
assign genpc_freeze = du_stall | flushpipe_r;
always @(posedge clk or posedge rst)
if (rst)
flushpipe_r <= #1 1'b0;
else if (icpu_ack_i | icpu_err_i)
//  else if (!if_stall)
flushpipe_r <= #1 flushpipe;
else if (!flushpipe)
flushpipe_r <= #1 1'b0;
file://----------------in or1200_except.v--------------------------
assign flushpipe = except_flushpipe | pc_we | extend_flush;
assign except_start = (except_type != `OR1200_EXCEPT_NONE) & extend_flush;
2)my analysis
When extend_flush deasserts,except_start also deasserts,but genpc_freeze
still keep high untill next clock.
So on next clock pc_reg changes to except vector's start address,pc changes
to next instruction of the vector,
icpu_cycstb_o assert,but at this time icpu_adr_o is equal to pc,but not
except vector's start address.
So the first instruction is skipped because of the bug of logic.

3)The testbench file,or1200_define.v and wave.do are in attachment.


????????????????qcpassed
????????????????qcpassed@sina.com
????????????????????2003-04-11


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