Apple-2-HW
/
GR8RAM
mirror of https://github.com/garrettsworkshop/GR8RAM.git
1
0
Fork 1
Code Issues Projects Releases Wiki Activity

Removed state counter reset

This commit is contained in:
Zane Kaminski 2019-12-21 01:46:05 -05:00
parent 79dd794f45
commit 85e3eb627d
1 changed files with 36 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

84
cpld/GR8RAM.v
View File

@ -60,9 +60,7 @@ module GR8RAM(C7M, C7M_2, Q3, PHI0in, PHI1in, nRES, nMode,
inout [7:0] D = DOE ? Dout : 8'bZ;
/* Inhibit output */
wire AROMSEL;
LCELL AROMSEL_MC (.in(/*(A[15:12]==4'hD | A[15:12]==4'hE | A[15:12]==4'hF) & nWE & ~MODE*/0), .out(AROMSEL));
output nINH = AROMSEL ? 1'b0 : 1'bZ;
output nINH = 1'bZ;
/* DRAM and ROM Control Signals */
output nRCS = ~((~nIOSEL | (~nIOSTRB & IOROMEN)) & CSDBEN); // ROM chip select
@ -108,25 +106,30 @@ module GR8RAM(C7M, C7M_2, Q3, PHI0in, PHI1in, nRES, nMode,
// 1st rising edge of C7M in PHI0 (S3)
always @(posedge C7M, negedge nRES) begin
if (~nRES) begin // Reset
PHI1reg <= 0;
PHI0seen <= 0;
S <= 0;
Ref <= 0;
// Synchronize state counter to S1 when just entering PHI1
PHI1reg <= PHI1; // Save old PHI1
if (~PHI1) PHI0seen <= 1; // PHI0seen set in PHI0
S <= (PHI1 & ~PHI1reg & PHI0seen) ? 4'h1 :
S==0 ? 3'h0 :
S==7 ? 3'h7 : S+1;
// Refresh counter allows DRAM refresh once every 13 cycles
if (S==3) Ref <= (Ref[3:2]==2'b11) ? 4'h0 : Ref+1;
// Only drive Apple II data bus after state 4 to avoid bus fight.
// Thus we wait 1.5 7M cycles (210 ns) into PHI0 before driving.
// Same for driving the ROM/SRAM data bus (RD).
// Similarly, only select the ROM chip starting at the end of S4.
// This provides address setup time for write operations and
// minimizes power consumption.
CSDBEN <= S==4 | S==5 | S==6 | S==7;
end
always @(posedge C7M, negedge nRES) begin
if (~nRES) begin
REGEN <= 0;
IOROMEN <= 0;
CSDBEN <= 0;
end else begin
// Synchronize state counter to S1 when just entering PHI1
PHI1reg <= PHI1; // Save old PHI1
if (~PHI1) PHI0seen <= 1; // PHI0seen set in PHI0
S <= (PHI1 & ~PHI1reg & PHI0seen) ? 4'h1 :
S==0 ? 3'h0 :
S==7 ? 3'h7 : S+1;
// Refresh counter allows DRAM refresh once every 13 cycles
if (S==3) Ref <= (Ref[3:2]==2'b11) ? 4'h0 : Ref+1;
// Disable IOSTRB ROM when accessing 0xCFFF.
if (S==3 & ~nIOSTRB & A[10:0]==11'h7FF) IOROMEN <= 1'b0;
@ -135,14 +138,6 @@ module GR8RAM(C7M, C7M_2, Q3, PHI0in, PHI1in, nRES, nMode,
// Enable IOSTRB ROM when accessing CnXX in IOSEL ROM.
if (S==4 & ~nIOSEL) IOROMEN <= 1'b1;
// Only drive Apple II data bus after state 4 to avoid bus fight.
// Thus we wait 1.5 7M cycles (210 ns) into PHI0 before driving.
// Same for driving the ROM/SRAM data bus (RD).
// Similarly, only select the ROM chip starting at the end of S4.
// This provides address setup time for write operations and
// minimizes power consumption.
CSDBEN <= S==4 | S==5 | S==6 | S==7;
end
end
@ -189,31 +184,24 @@ module GR8RAM(C7M, C7M_2, Q3, PHI0in, PHI1in, nRES, nMode,
/* DRAM RAS/CAS */
always @(posedge C7M, negedge nRES) begin
if (~nRES) begin
RASr <= 1'b0; ASel <= 1'b0; CASr <= 1'b0;
end else begin
RASr <= (S==1 & Ref==0) | // Refresh
(S==4 & RAMSEL & nWE) | // Read: Early RAS
(S==5 & RAMSEL & ~nWE); // Write: Late RAS
RASr <= (S==1 & Ref==0) | // Refresh
(S==4 & RAMSEL & nWE) | // Read: Early RAS
(S==5 & RAMSEL & ~nWE); // Write: Late RAS
// Multiplex DRAM address in at end of S4 through S6.
ASel = (RAMSEL & nWE & S==4) | // Read: mux address early
(RAMSEL & ~nWE & S==5); // Write: mux address late
// Multiplex DRAM address in at end of S4 through S6.
ASel = (RAMSEL & nWE & S==4) | // Read: mux address early
(RAMSEL & ~nWE & S==5); // Write: mux address late
// Read: long, early CAS, gated later by RAMSEL
CASr <= (RAMSEL & ~nWE & (S==5 | S==6 | S==7));
end
// Read: long, early CAS, gated later by RAMSEL
CASr <= (RAMSEL & ~nWE & (S==5 | S==6 | S==7));
end
always @(negedge C7M, negedge nRES) begin
if (~nRES) begin RASf <= 1'b0; CAS0f <= 1'b0; CAS1f <= 1'b0;
end else begin
RASf <= (S==4 & RAMSEL & nWE) | // Read: Early RAS
(S==5 & RAMSEL & ~nWE); // Write: Late RAS
RASf <= (S==4 & RAMSEL & nWE) | // Read: Early RAS
(S==5 & RAMSEL & ~nWE); // Write: Late RAS
CAS0f <= (S==1 & Ref==0) | // Refresh
(S==6 & RAMSEL & ~Addr[22] & ~nWE); // Write: Late CAS
CAS1f <= (S==1 & Ref==0) | // Refresh
(S==6 & RAMSEL & Addr[22] & ~nWE); // Write: Late CAS
end
CAS0f <= (S==1 & Ref==0) | // Refresh
(S==6 & RAMSEL & ~Addr[22] & ~nWE); // Write: Late CAS
CAS1f <= (S==1 & Ref==0) | // Refresh
(S==6 & RAMSEL & Addr[22] & ~nWE); // Write: Late CAS
end
endmodule