fixed 2 more bugs in h2d/fifo control

ahci/ahci_fis_receive.v

@@ -393,7 +393,7 @@ localparam DATA_TYPE_ERR =      3;
         
         if (reg_sdb[1])                       sactive0 <=        hba_data_in[0];
         
-        if (hba_rst || reg_sdb[0] || clear_xfer_cntr) xfer_cntr_r[31:2] <= 0;
+        if (hba_rst || reg_sdb[0] || clear_xfer_cntr)           xfer_cntr_r[31:2] <= 0;
         else if (reg_ps[4] || reg_ds[5])                        xfer_cntr_r[31:2] <= {reg_ds[5]?hba_data_in[31:16]:16'b0,
                                                                                       hba_data_in[15:2]} + hba_data_in[1]; // round up
         else if ((decr_dwcw || decr_dwcr) && !xfer_cntr_zero_r) xfer_cntr_r[31:2] <= {xfer_cntr_r[31:2]} - 

ahci/ahci_sata_layers.v

@@ -24,7 +24,12 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/> .
  */
 `timescale 1ns/1ps
-
+//`define CHECK_LOW_H2D_FIFO // reduce actual h2d fifo size during simulation, to test h2d_ready
+/** TODO:
+ 1. Check nothing is left in H2D FIFO after data is sent  - it will happen after DPATp received.
+ 2. Make DPATp an error? It is not easy to insert 0x00000046" data FIS header before remaining data (already in FIS)
+  - it may also hold fis_transmit, as maximal data fis is 4x of the FIFO size. 
+*/
 module  ahci_sata_layers #(
 `ifdef USE_DATASCOPE
     parameter ADDRESS_BITS =         10, //for datascope
@@ -105,6 +110,9 @@ module  ahci_sata_layers #(
     output  wire        txn_out,
     input   wire        rxp_in,
     input   wire        rxn_in,
+    output              debug_is_data, // @clk (sata clk) - last symbol was data output
+    output              debug_dmatp,  // @clk (sata clk) - received CODE_DMATP
+    
 `ifdef USE_DATASCOPE
 // Datascope interface (write to memory that can be software-read)
     output                    datascope_clk,
@@ -142,6 +150,13 @@ module  ahci_sata_layers #(
     localparam H2D_TYPE_FIS_HEAD = 1;
     localparam H2D_TYPE_FIS_LAST = 2;
     
+`ifdef SIMULATION
+    `ifdef CHECK_LOW_H2D_FIFO
+        localparam H2D_FIFO_THRESHOLD = 4; // to test h2d_ready - will turn off frequently, much earlier than fifo almost full
+    `endif
+`endif
+    
+    
     wire               phy_ready;        // active when GTX gets aligned output
     wire               link_established; // Received 3 back-to-back non-ALIGNp 
     wire        [31:0] ll_h2d_data_in;
@@ -186,7 +201,9 @@ module  ahci_sata_layers #(
     wire       [FIFO_ADDR_WIDTH:0] d2h_fill;
     wire                           d2h_nempty;
     wire                           h2d_fifo_rd = h2d_nempty && ll_strobe_out; // TODO: check latency in link.v
-    wire                           h2d_fifo_wr = h2d_valid;
+//    wire                           h2d_fifo_wr = h2d_valid;
+//2016.12.10
+    wire                           h2d_fifo_wr = h2d_valid && h2d_ready; // or should valid depend on ready in the fis_transmit?
     
     wire                           d2h_fifo_rd = d2h_valid && d2h_ready;
     wire                           d2h_fifo_wr = ll_d2h_valid || fis_over_r; // fis_over_r will push FIS end to FIFO
@@ -205,7 +222,18 @@ assign ll_h2d_last =  (h2d_type_out == H2D_TYPE_FIS_LAST);
 assign d2h_valid = d2h_nempty;
 assign d2h_many =  |d2h_fill[FIFO_ADDR_WIDTH:3]; // 
 
-assign h2d_ready = !h2d_fill[FIFO_ADDR_WIDTH] && !(&h2d_fill[FIFO_ADDR_WIDTH:3]);
+// assign h2d_ready = !h2d_fill[FIFO_ADDR_WIDTH] && !(&h2d_fill[FIFO_ADDR_WIDTH:3]);
+// 2016:12:10 sometimes overflow happened because of a BUG 
+`ifdef SIMULATION
+    `ifdef CHECK_LOW_H2D_FIFO
+        assign h2d_ready = !h2d_fill[FIFO_ADDR_WIDTH] && (h2d_fill < ((1 << BITS_TO_START_XMIT) + H2D_FIFO_THRESHOLD ));
+    `else
+        assign h2d_ready = !h2d_fill[FIFO_ADDR_WIDTH] && !(&h2d_fill[FIFO_ADDR_WIDTH-1:3]); // same as with synthesis
+    `endif
+`else
+        assign h2d_ready = !h2d_fill[FIFO_ADDR_WIDTH] && !(&h2d_fill[FIFO_ADDR_WIDTH-1:3]);
+`endif
+
 assign ll_d2h_almost_full   = d2h_fill[FIFO_ADDR_WIDTH] || &d2h_fill[FIFO_ADDR_WIDTH-1:6]; // 63 dwords (maybe use :5?) - time to tell device to stop 
 
 //    assign ll_frame_req_w = !ll_frame_busy && h2d_pending && (((h2d_type == H2D_TYPE_FIS_LAST) && h2d_fifo_wr ) || (|h2d_fill[FIFO_ADDR_WIDTH : BITS_TO_START_XMIT]));
@@ -317,7 +345,9 @@ assign debug_phy = debug_phy0;
         .phy_err_in       (ph2ll_err_out),         // input[3:0] wire   // disperr | notintable
         // to phy
         .phy_data_out     (ll2ph_data_in),         // output[31:0] wire 
-        .phy_isk_out      (ll2ph_charisk_in),       // output[3:0] wire   // charisk
+        .phy_isk_out      (ll2ph_charisk_in),      // output[3:0] wire   // charisk
+        .debug_is_data    (debug_is_data),         // output reg @clk (sata clk) - last symbol was data output
+        .debug_dmatp      (debug_dmatp),           // output reg @clk (sata clk) - received CODE_DMATP
         .debug_out        (debug_link)
     );
     

ahci/ahci_top.v

@@ -190,6 +190,8 @@ module  ahci_top#(
     
 
     output             irq, // CPU interrupt request
+    input              debug_link_send_data, // @posedge sata_clk - last symbol was data output (to count sent out)
+    input              debug_link_dmatp,     // link received DMATp from device
     
 `ifdef USE_DATASCOPE
 // Datascope interface (write to memory that can be software-read)
@@ -1204,6 +1206,7 @@ wire [9:0] xmit_dbg_01;
                 .soft_write_addr (soft_write_addr), // input[9:0] 
                 .soft_write_data (soft_write_data), // input[31:0] 
                 .soft_write_en   (soft_write_en), // input
+                .cfis            (fsnd_cfis_xmit), // input command FIS - to reset dword counter
                 .h2d_data        (h2d_data), // input[31:0] 
                 .h2d_type        (h2d_type), // input[1:0] 
                 .h2d_valid       (h2d_valid), // input
@@ -1212,6 +1215,8 @@ wire [9:0] xmit_dbg_01;
                 .d2h_type        (d2h_type), // input[1:0] 
                 .d2h_valid       (d2h_valid), // input
                 .d2h_ready       (d2h_ready), // input
+                .debug_link_send_data(debug_link_send_data), // input
+                .debug_link_dmatp  (debug_link_dmatp),        // link received DMATp from device
                 .datascope_clk   (datascope_clk), // output
                 .datascope_waddr (datascope_waddr), // output[9:0] reg 
                 .datascope_we    (datascope_we), // output
@@ -1327,6 +1332,8 @@ module datascope_timing #(
     input              [31:0] soft_write_data, 
     input                     soft_write_en,
     
+    input                     cfis, // to reset send counter
+    
     // outgoing FISes
     input              [31:0] h2d_data,     // 32-bit data from the system memory to HBA (dma data)
     input              [ 1:0] h2d_type,     // 0 - data, 1 - FIS head, 2 - FIS END (make FIS_Last?)
@@ -1341,6 +1348,8 @@ module datascope_timing #(
     input                     d2h_valid,   // Data available from the transport layer in FIFO                
     input                     d2h_ready,   // This module or DMA consumes DWORD
     
+    input                     debug_link_send_data, // @posedge mclk (sata_clk, 75MHz)  - last symbol was data output (to count sent out)
+    input                     debug_link_dmatp,     // link received DMATp from device
     output                        datascope_clk,
     output reg [ADDRESS_BITS-1:0] datascope_waddr,
     output                        datascope_we,
@@ -1360,6 +1369,9 @@ module datascope_timing #(
     reg                [31:0] fis_data;
     reg                [27:0] cur_time;
     reg                       was_h2d_last;
+    reg                       h2d_ready_d; // delayed h2d_ready to count 1->0 transitions
+    reg                [ 7:0] h2d_nready_cntr; // count (infrequent) events when h2d FIFO turns off ready 
+//    reg                       
     
     wire                      fis_start = (h2d_valid && h2d_ready && (h2d_type == 1)) ||
                                           (d2h_valid && d2h_ready && (d2h_type == 1));
@@ -1367,11 +1379,44 @@ module datascope_timing #(
 //    wire                      fis_end_we = (fis_left == 0) || fis_end;
 
     wire                      pre_we_w =  fis_run && (d2h_valid?(d2h_valid && d2h_ready):(h2d_valid && h2d_ready));
+    
+    reg                       fis_run_d2;
+    reg                       fis_run_d3;
+    reg                       fis_run_d4; // to read non 0x39 d2h fis
+    reg                       fis_run_d5; // number of dwords sent by link a s data symbols
+//  reg                       fis_first;
+    reg                       data_fis;
     reg                       pre_we_r;                                      
-    reg                       we_r;                                      
+    reg                       we_r;
+    
+    wire                      inc_dw_cntr =  fis_run && (d2h_valid?(d2h_ready && (d2h_type == 0)):(h2d_valid && h2d_ready));
+    
+    wire is_cfis_w = h2d_valid && (h2d_data[ 7: 0] == 8'h27) && // valid @ fis_start
+                                 ((h2d_data[23:16] == 8'h25) || // Read DMA Extended
+                                  (h2d_data[23:16] == 8'h35) || // Write DMA Extended
+                                  (h2d_data[23:16] == 8'hC8) || // Read DMA
+                                  (h2d_data[23:16] == 8'hCA));   // Write DMA
+    reg  is_cfis_r;                                               
+    reg                [23:0] last_dma_cmd;
+    reg                       set_dma_count;                                      
+    reg                [21:0] dw_count;
+    wire                [7:0] fis_data_w = d2h_valid ? d2h_data[7:0] : h2d_data[7:0]; 
+    reg                [31:0] non_dma_act; // last D2H FIS that was not DMA activate, received after DMA/IO command
+    reg                       set_non_dma_act;
+    reg                [21:0] link_count;
+    reg                [21:0] link_count_latched;
+    
+    reg                       reset_link_count; // data FIS from dma command until
+    reg                       was_link_dmatp;   //
+    
+//    input              debug_link_dmatp,      // link received DMATp from device
+    
+    
     assign datascope_we =  we_r;
     assign datascope_clk = clk;
     
+    
+    
     always @ (posedge clk) begin
         was_h2d_last <= h2d_type[1] && h2d_valid && h2d_ready;
     
@@ -1384,17 +1429,29 @@ module datascope_timing #(
         else if (write_tag_w)         pend_punch_time <= 1;
         else if (write_punch_time)    pend_punch_time <= 0;
         
-        if (write_punch_time || fis_start) datascope_di <= {write_punch_time?{1'b1,punch_tag}:{3'b0,d2h_valid},cur_time};
-        else if (fis_we)                   datascope_di <= fis_data;
-        else if (!fis_run && fis_run_d)    datascope_di <= {19'h7fff8, fis_len};
-        
+        if (write_punch_time || fis_start)   datascope_di <= {write_punch_time?{1'b1,punch_tag}:{3'b0,d2h_valid},cur_time};
+        else if (fis_we)                     datascope_di <= fis_data;
+        else if (!fis_run    && fis_run_d)   datascope_di <= {19'h7fff8, fis_len};
+        else if (!fis_run_d  && fis_run_d2)  datascope_di <= {10'h2a8,   dw_count};
+        else if (!fis_run_d2 && fis_run_d3)  datascope_di <= {8'h55,   last_dma_cmd};
+        else if (!fis_run_d3 && fis_run_d4)  datascope_di <= non_dma_act;
+        else if (!fis_run_d4 && fis_run_d5)  datascope_di <= {h2d_nready_cntr[7:0], was_link_dmatp, 1'b0, link_count_latched};
+
         pre_we_r <= pre_we_w || fis_start ;
     
-        we_r <= write_punch_time || fis_start || (fis_we ? pre_we_r : (!fis_run && fis_run_d));
+//        we_r <= write_punch_time || fis_start || (fis_we ? pre_we_r : (!fis_run && fis_run_d));
+        we_r <= write_punch_time || fis_start || (fis_we ? pre_we_r : (!fis_run && (fis_run_d || fis_run_d2 || fis_run_d3 || fis_run_d4  || fis_run_d5))); // 3 after
         
         if     (fis_start) fis_left <= FIS_LEN - 1;
         else if (pre_we_w) fis_left <= fis_left - 1;
         
+//        if     (fis_start) fis_first <= 1;
+//       else if (pre_we_w) fis_first <= 0;
+
+        if      (fis_end)               data_fis <= 0;
+//        else if (pre_we_w && fis_start) data_fis <= fis_data_w == 8'h46;
+        else if (fis_start) data_fis <= fis_data_w == 8'h46;
+        
         if      (rst)                        fis_we <= 0;
         else if (fis_start)                  fis_we <= 1;
         else if ((fis_left == 0) || fis_end) fis_we <= 0;
@@ -1403,7 +1460,46 @@ module datascope_timing #(
         else if (fis_start)  fis_run <= 1;
         else if (fis_end)    fis_run <= 0;
 
-        fis_run_d <= fis_run;
+        fis_run_d <=  fis_run;
+        fis_run_d2 <= fis_run_d;
+        fis_run_d3 <= fis_run_d2;
+        fis_run_d4 <= fis_run_d3; 
+        fis_run_d5 <= fis_run_d4;
+               
+        if      (cfis)                    dw_count <= 0;
+        else if (inc_dw_cntr && data_fis) dw_count <= dw_count + 1;
+        
+        if      (rst)                                reset_link_count <= 0;
+        else if (cfis)                               reset_link_count <= 1;
+        else if (fis_start && (fis_data_w == 8'h46)) reset_link_count <= 0;
+
+        if      (reset_link_count)     link_count <= 0;
+        else if (debug_link_send_data) link_count <= link_count + 1; // will only be valid later, latch at next fis start
+        
+        if (fis_start) link_count_latched <= link_count;
+        
+        
+        if      (reset_link_count)     was_link_dmatp <= 0;
+        else if (debug_link_dmatp)     was_link_dmatp <= 1;
+        
+        h2d_ready_d <= h2d_ready;
+        
+        if      (rst)                       h2d_nready_cntr <= 0;
+        else if (!h2d_ready && h2d_ready_d) h2d_nready_cntr <= h2d_nready_cntr+1;
+        
+        
+        if (fis_start) is_cfis_r <= is_cfis_w;
+        
+        if (fis_start && is_cfis_w) last_dma_cmd[23:16] <= h2d_data[23:16]; // command code
+        
+        set_dma_count <=  (fis_len == 3) && h2d_valid && h2d_ready && is_cfis_r;
+        
+        if (set_dma_count) last_dma_cmd[15:0] <= fis_data[15:0];
+        
+        set_non_dma_act <= fis_start && d2h_valid && (fis_data_w != 8'h39);
+        
+        if      (set_dma_count)   non_dma_act <= 32'h33333333;
+        else if (set_non_dma_act) non_dma_act <= fis_data;
         
         if     (fis_start) fis_len <= d2h_valid? 0 : 1;
         else if (pre_we_w) fis_len <= fis_len + 1;

ahci/sata_ahci_top.v

@@ -239,6 +239,8 @@
     
     reg          [2:0] nhrst_r;
     wire               hrst = !nhrst_r[2];
+    wire               debug_link_send_data; // @sata clk - last symbol was data output
+    wire               debug_link_dmatp;     // @clk (sata clk) - received CODE_DMATP
     
     wire [FREQ_METER_WIDTH-1:0] xclk_period;
 `ifdef USE_DATASCOPE
@@ -403,7 +405,8 @@
         .sctl_ipm          (sctl_ipm),          // output[3:0] 
         .sctl_spd          (sctl_spd),          // output[3:0] 
         .irq               (irq),               // output
-
+        .debug_link_send_data (debug_link_send_data), // input @posedge sata_clk - last symbol was data output (to count sent out)
+        .debug_link_dmatp  (debug_link_dmatp),        // link received DMATp from device
 `ifdef USE_DATASCOPE
         .datascope1_clk    (datascope_clk),     // input
         .datascope1_waddr  (datascope_waddr),   // input[9:0] 
@@ -489,6 +492,10 @@
         .txn_out           (TXN),               // output wire 
         .rxp_in            (RXP),               // input wire 
         .rxn_in            (RXN),               // input wire
+        .debug_is_data     (debug_link_send_data), //output  @clk (sata clk) - last symbol was data output
+        .debug_dmatp       (debug_link_dmatp),  // @clk (sata clk) - received CODE_DMATP
+        
+        
 `ifdef USE_DATASCOPE
         .datascope_clk     (datascope_clk),     // output
         .datascope_waddr   (datascope_waddr),   // output[9:0] 

device/sata_device.v

@@ -47,7 +47,8 @@ module sata_device(
 //    reg  [31:0] DEV_DATA;
     integer DEV_DATA;
 //`endif
-
+//`define TERMINATE_DMA_H2D
+//`undef TERMINATE_DMA_H2D
 wire            phy_ready;
 
 wire    [31:0]  phy2dev_data;
@@ -569,6 +570,10 @@ task linkMonitorFIS;
                     cnt = cnt + 1;
                     if (cnt <= 2048)
                         pause = pause + receive_data_pause[cnt];
+`ifdef TERMINATE_DMA_H2D
+        linkSendPrim("DMAT");
+`endif
+                        
                 end    
             end
             @ (posedge clk)

host/link.v

@@ -99,6 +99,8 @@ module link #(
     // to phy
     output  wire    [DATA_BYTE_WIDTH*8 - 1:0] phy_data_out,
     output  wire    [DATA_BYTE_WIDTH   - 1:0] phy_isk_out,   // charisk
+    output reg                                debug_is_data, // @clk (sata clk) - last symbol was data output
+    output reg                                debug_dmatp,  // @clk (sata clk) - received CODE_DMATP
     // debug
     output                             [31:0] debug_out      //
 );
@@ -580,6 +582,10 @@ begin
 end
 endgenerate
 
+always @ (posedge clk) begin
+     debug_dmatp <= rcvd_dword[CODE_DMATP];
+end
+
 // select which primitive shall be sent 
 wire    [PRIM_NUM - 1:0]    select_prim;
 assign  select_prim[CODE_SYNCP]     = ~alignes_pair & (state_idle | state_sync_esc | state_rcvr_wait | state_reset);
@@ -618,6 +624,10 @@ always @ (posedge clk)
                     {DATA_BYTE_WIDTH*8{select_prim[CODE_CRC]}}    & prim_data[CODE_CRC]    |
                     {DATA_BYTE_WIDTH*8{select_prim[CODE_DATA]}}   & prim_data[CODE_DATA];
 
+always @ (posedge clk)
+    debug_is_data <=  select_prim[CODE_DATA];
+
+
 always @ (posedge clk)
     to_phy_isk <= rst | ~select_prim[CODE_DATA] & ~select_prim[CODE_CRC] ? {{(DATA_BYTE_WIDTH - 1){1'b0}}, 1'b1} : {DATA_BYTE_WIDTH{1'b0}} ;
 

includes/ahci_defaults.vh

@@ -2,6 +2,6 @@
 , .INIT_08 (256'h000000000024000600000000000000000000000080000C000000000080000800)
 , .INIT_09 (256'h000000000000000000000000000000000000000000000000FFFFFFFF00000000)
 , .INIT_0B (256'h0000000000000000000000000000003300000000000000000000000000000000)
-, .INIT_0C (256'h00000000000000000000000000000000000000000101000B001000000001FFFE)
+, .INIT_0C (256'h000000000000000000000000000000000000000001010011001000000001FFFE)
 , .INIT_0D (256'h000001000000000000000040000000000001FFFE000000008000000000000000)
 , .INIT_0E (256'h0000000000000000000000000000000000000000000000000000000040000001)

includes/ahci_localparams.vh

@@ -97,7 +97,7 @@
 // RO: HBA Revision ID
     localparam PCI_Header__RID__RID__ADDR = 'h62;
     localparam PCI_Header__RID__RID__MASK = 'hff;
-    localparam PCI_Header__RID__RID__DFLT = 'hb;
+    localparam PCI_Header__RID__RID__DFLT = 'h11;
 // RO: Base Class Code: 1 - Mass Storage Device
     localparam PCI_Header__CC__BCC__ADDR = 'h62;
     localparam PCI_Header__CC__BCC__MASK = 'hff000000;

py393sata/create_ahci_registers.py

@@ -31,7 +31,7 @@ __status__ = "Development"
 """
 **** Modify next value for new file versions, re-run this file  *****
 """
-RID = 0x0b  # Revision ID
+RID = 0x011  # Revision ID
 VID = 0xfffe # What to use for non-PCI "vendorID"?
 DID = 0x0001
 SSVID = 0xfffe

py393sata/x393sata.py

@@ -1497,6 +1497,17 @@ if __name__ == "__main__":
 
 
     """
+camogm_test -d /dev/sda2 -b 4194304 -c 30000
+    
+    
+dd if=/dev/sda skip=257142656 count=1 | hexdump -e '"%08_ax: "' -e ' 16/4 "%08x " "\n"'
+cat /sys/devices/soc0/amba@0/80000000.elphel-ahci/lba_current
+cat /sys/devices/soc0/amba@0/80000000.elphel-ahci/lba_start    
+ 
+camogm_test -d /dev/sda2 -b 4194304 -c 10000
+ 
+    
+    
 x393sata.py
 modprobe ahci_elphel &
 sleep 2
@@ -1520,7 +1531,8 @@ import x393_mem
 mem = x393_mem.X393Mem(1,0,1)
 sata = x393sata.x393sata()
 hex(mem.read_mem(sata.get_reg_address('PCI_Header__RID')))
-
+hex([((mem.read_mem(0x80000ffc) >> 10) & 0xffc) + 0x80001000,mem.mem_dump (0x80001000, 0x400,4),sata.reg_status()][0])
+ 
 sata.setup_pio_read_identify_command()
 
 sata.dd_read_dma_ext(142615470, 512, 512)

tb/tb_ahci.tf

@@ -1120,6 +1120,9 @@ localparam ATA_RDMA_EXT = 'h25; // Read DMA devices that support 48-bit Addressi
                                                (ATA_RDMA_EXT << 16) | // Command = 0x25 (READ_DMA_EXT)
                                               ( 0 << 24);        // features = 0 ?
             // All other 4 DWORDs are 0 for this command
+            
+            sysmem[(COMMAND_TABLE >> 2) + 3] = 1; // count
+            
             // Set PRDT (four items)
             // PRDT #1
             sysmem[((COMMAND_TABLE + PRD_OFFSET) >> 2) +  0] = SYS_MEM_START + IDENTIFY_BUF; // not shifted
@@ -1178,6 +1181,7 @@ localparam ATA_RDMA_EXT = 'h25; // Read DMA devices that support 48-bit Addressi
             sysmem[(COMMAND_TABLE >> 2) + 1] = lba & 'hffffff;    // 24 LSBs of LBA (48-bit require different ATA command)
             sysmem[(COMMAND_TABLE >> 2) + 3] = 1;                 // 1 logical sector (0 means 256)
             // All other DWORDs are 0 for this command
+            sysmem[(COMMAND_TABLE >> 2) + 3] = 1; // count
             // Set PRDT (four items)
             // PRDT #1
             sysmem[((COMMAND_TABLE + PRD_OFFSET) >> 2) +  0] = SYS_MEM_START + IDENTIFY_BUF; // not shifted
@@ -1227,6 +1231,7 @@ localparam ATA_RDMA_EXT = 'h25; // Read DMA devices that support 48-bit Addressi
             sysmem[(COMMAND_TABLE >> 2) + 1] = lba & 'hffffff;    // 24 LSBs of LBA (48-bit require different ATA command)
             sysmem[(COMMAND_TABLE >> 2) + 3] = 1;                 // 1 logical sector (0 means 256)
             // All other DWORDs are 0 for this command
+            sysmem[(COMMAND_TABLE >> 2) + 3] = 1; // count
             // Set PRDT (four items)
             // PRDT #1
             sysmem[((COMMAND_TABLE + PRD_OFFSET) >> 2) +  0] = SYS_MEM_START + IDENTIFY_BUF; // not shifted