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From: cvs at opencores.org<cvs@o...>
Date: Tue Oct 25 07:39:10 CEST 2005
Subject: [cvs-checkins] MODIFIED: risc16f84 ...
Date: 00/05/10 25:07:39

Modified: risc16f84 risc16f84_clk2x.v
Log:
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Revision Changes Path
1.2 risc16f84/risc16f84_clk2x.v

http://www.opencores.org/cvsweb.shtml/risc16f84/risc16f84_clk2x.v.diff?r1=1.1&r2=1.2

(In the diff below, changes in quantity of whitespace are not shown.)

Index: risc16f84_clk2x.v
===================================================================
RCS file: /cvsroot/jclaytons/risc16f84/risc16f84_clk2x.v,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -b -r1.1 -r1.2
--- risc16f84_clk2x.v 25 Oct 2005 05:02:00 -0000 1.1
+++ risc16f84_clk2x.v 25 Oct 2005 05:39:08 -0000 1.2
@@ -150,6 +150,9 @@
// an error such that all subtraction results were off by 1.
// Obviously, this was unacceptable, and I think it has been fixed
// by the new signals "c_subtract_zero" and "c_dig_subtract_zero"
+// Update: 10/24/05 Added code patches to fix interrupt bug and status flag updates
+// when using literal value of 0x03. These bugs were reported by
+// an opencores.org user. Added three "disable_status_x" signals.
//
// Description
//---------------------------------------------------------------------------
@@ -342,6 +345,10 @@
reg c_dig_subtract_zero; // High for special case of C bit, when subtracting zero

wire next_exec_stall;
+ // Three signals used to disable status flag updates. Fixes bug when literal 0x03 is used.
+wire disable_status_z;
+wire disable_status_c;
+wire disable_status_dc;

//--------------------------------------------------------------------------
// Instantiations
@@ -435,6 +442,19 @@
// construct bit-mask for logical operations and bit tests
assign mask_node = 1 << inst_reg[9:7];

+// disable write access for status flags
+assign disable_status_z = (inst_addwf || inst_andwf || inst_clrf ||
+ inst_clrw || inst_comf || inst_decf ||
+ inst_incf || inst_iorwf || inst_movf ||
+ inst_subwf || inst_xorwf || inst_addlw ||
+ inst_andlw || inst_iorlw || inst_iorlw ||
+ inst_sublw || inst_xorlw) ? 1:0;
+assign disable_status_c = (inst_addwf || inst_subwf || inst_rlf ||
+ inst_rrf || inst_addlw || inst_sublw ) ? 1:0;
+assign disable_status_dc = (inst_addwf || inst_subwf || inst_addlw ||
+ inst_sublw ) ? 1:0;
+
+
// Create the exec_stall signal, based on the contents of the currently
// executing instruction (inst_reg). next_exec_stall reflects the state
// to assign to exec_stall following the conclusion of the next Q4 state.
@@ -800,6 +820,7 @@

if (writew_node) w_reg <= aluout; // write W reg

+
// 2-5-2-2. Set data RAM/special registers,
if (writeram_node)
begin
@@ -807,7 +828,8 @@
begin
status_reg[7:5] <= aluout[7:5]; // write IRP,RP1,RP0
// status(4),status(3)...unwritable, see below (/PD,/T0 part)
- status_reg[1:0] <= aluout[1:0]; // write DC,C
+ if( ~disable_status_c ) status_reg[0] <= aluout[0]; // write C
+ if( ~disable_status_dc ) status_reg[1] <= aluout[1]; // write DC
end
if (addr_fsr) fsr_reg <= aluout; // write FSR
if (addr_pclath) pclath_reg <= aluout[4:0]; // write PCLATH
@@ -817,7 +839,7 @@
end

// 2-5-2-3. Set/clear Z flag.
- if (addr_stat) status_reg[2] <= aluout[2]; // (dest. is Z flag)
+ if (addr_stat && ~disable_status_z) status_reg[2] <= aluout[2];
else if ( inst_addlw || inst_addwf || inst_andlw || inst_andwf
|| inst_clrf || inst_clrw || inst_comf || inst_decf
|| inst_incf || inst_movf || inst_sublw || inst_subwf
@@ -919,7 +941,7 @@

// Issue an interrupt when the interrupt is present.
// Also, do not issue an interrupt when there is a stall cycle coming!
-assign int_condition = (inte_sync_reg && ~exec_stall_reg && intcon_reg[7]);
+assign int_condition = (inte_sync_reg && ~exec_stall_reg && ~next_exec_stall && intcon_reg[7]);
// Interrupt must be pending
// Next processor cycle must not be a stall
// GIE bit must be set to issue interrupt