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DEV Card GALs disassembly and replacement.

==== U2104 ====

GAL22V10 .

Signals :

inputs :

^GAL pin^Signal|
|2|33.3 MHz clock|
|3| |
|4|/BR CPU1|
|5|/BR CPU0|
|6|/TS CPU0|
|7|TC1 CPU0|
|9|TC0 CPU0|
|10|TT1 CPU0|
|11|/TBST CPU0|

Inputs Pin 12,13,16 are grounded

Outputs:

^GAL Pin^Signal|
|17|/BG CPU1 (or R2124)|
|18|/BG CPU0|
|24|R2122 ??|
|27|delayed 1 … (Reset?)|

=== Signal logic: ===

/TBST - Transfer burst (active low)

/TS - Transfer start (active low)

/BR - Bus request by CPU (active low)

/BG - Bus grant to CPU (active low)

TC0-TC1 are the transfer code:

^[TC0:TC1]^Read^Write|
|00|Data transaction|Normal write|
|01|-|Copy-back line-fill|
|10|Instruction fetch|-|
|11|-|-|

TT0-TT4 are the transfer type of the transaction.

^[TT0:TT4]  ^Command  ^Transaction  |
|00000  |Clean block  |Address  |
|00100  |Flush block  |Address  |
|01000  |SYNC  |Address  |
|01100  |Kill block (**dcbz**)  |Address  |
|10000  |EIEIO  |Address  |
|10100  |Write via **ecowx**   |Nonburst write  |
|11000  |TLB invalidate  |Address  |
|11100  |Riad via **eciwx**   |Nonburst read  |
|00001  |Resv set via **lwarx**   |Address  |
|00101  |Resv clear via **stwcx**   |Address  |
|01001  |TLBSYNC  |Address  |
|01101  |ICBI  |Address  |
|1xx01  |-  |-  |
|00010  |write-with-flush  |Nonburst write  |
|00110  |write-with-kill  |Burst  |
|01010  |Read  |Nonburst read or burst  |
|01110  |read-with-intent-to-modify  |Burst  |
|10010  |write-with-flush-atomic  |Nonburst write  |
|10110  |-  |-  |
|11010  |Read atomic  |Nonburst read or burst  |
|11110  |read-with-intent-to-modify atomic  |Burst  |
|00×11  |-  |-  |
|01011  |read-with-no-intent-to-modify  |Nonburst read or burst  |
|01111  |-  |-  |
|1xx11  |-  |-  |

=== Possible implementation: ===
<file>

module u2104(clk,ntbst,nts,nbr,nbg,tt1,tc,unknownin,unknownout);
input wire clk;
input wire ntbst;
input wire nts;
input wire [1:0]nbr;
output wire [1:0]nbg;
input wire tt1;
input wire [1:0]tc;
input wire unknownin;
output wire unknownout;

reg[1:0] bgout;
assign nbg=unknownin?2'b11:bgout;

wire master_is_busy;

//grant master bus on any request or during the active transaction
//grant slave bus only when requested and master is not busy with anything
//don't grant the bus if bridgit is requesting it

always@(posedge clk)
   bgout<={(!master_is_busy & !br[1] & br[0])?0:1),{(!br0|master_is_busy)?0:1};

reg master_is_writing;
reg master_is_reading;

//master is considered busy if it's reading, writing or in the middle of the burst
assign master_is_busy=master_is_writing | master_is_reading | !ntbst;

//writing is any transaction start with data transfers and data type1 is 0
always @(posedge clk)
   master_is_writing<=(!ts & !tc[0] & !tt1);

//reading is any transaction start with type1 is 1
always @(posedge clk)
   master_is_reading<=(!ts & tt1);

//just delayed 1 for now, didn't see any activity
reg delay;

always @(posedge clk)
    delay<=1'b1;

assign unknownout=delay;

endmodule

</file>
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