AddingPeripherals.mdwn

diff --git a/docs/AddingPeripherals.mdwn b/docs/AddingPeripherals.mdwn
index 38d8c4edb3cdce4f317382c573af585ed4feacab..736a7c3f77e4e2ee8a39690124e3a74ff877ef99 100644 (file)
--- a/docs/AddingPeripherals.mdwn
+++ b/docs/AddingPeripherals.mdwn
@@ -752,3 +752,79 @@ This generates *one* mkConnection for each multi-entry pintype, and here we
 match up with the "InterfaceMultiBus" class from the specification side,
 where pin entries with numerically matching names were "grouped" into single
 multi-bit declarations.
+
+## Adjusting the BSV Interface to a get/put style
+
+For various reasons, related to BSV not permitting wires to be connected
+back-to-back inside the pinmux code, a get/put style of interface had to
+be done.  This requirement has a knock-on effect up the chain into the
+actual peripheral code.  So now the actual interface (Ifc\_sdram\_out)
+has to be converted.  All straight methods (outputs) are converted to Get,
+and Action methods (inputs) converted to Put.  Also, it is just plain
+sensible not to use Bool but to use Bit#, and for the pack / unpack to
+be carried out in the interface.  After conversion, the code looks like this:
+
+    interface Ifc_sdram_out;
+        (*always_enabled, always_ready*)
+        interface Put#(Bit#(64)) ipad_sdr_din;
+        interface Get#(Bit#(64)) osdr_dout;
+        interface Get#(Bit#(64)) osdr_den_n;
+        interface Get#(Bit#(1))  osdr_cke;
+        interface Get#(Bit#(1))  osdr_cs_n;
+        interface Get#(Bit#(1))  osdr_ras_n;
+        interface Get#(Bit#(1))  osdr_cas_n;
+        interface Get#(Bit#(1))  osdr_we_n;
+        interface Get#(Bit#(8))  osdr_dqm;
+        interface Get#(Bit#(2))  osdr_ba;
+        interface Get#(Bit#(13)) osdr_addr;
+
+        method Bit#(9) sdram_sdio_ctrl;
+        interface Clock sdram_clk;
+    endinterface
+
+Note that osdr\_den\_n is now **64** bit **not** 8, as discussed above.
+After conversion, the code looks like this:
+
+    interface Ifc_sdram_out ifc_sdram_out;
+
+        interface ipad_sdr_din = interface Put
+            method Action put(Bit#(64) in)
+                sdr_cntrl.ipad_sdr_din <= in;
+            endmethod
+        endinterface;
+
+        interface osdr_dout = interface Get
+          method ActionValue#(Bit#(64)) get;
+            return sdr_cntrl.osdr_dout();
+          endmethod
+        endinterface;
+
+        interface osdr_den_n = interface Get
+            method ActionValue#(Bit#(64)) get;
+                Bit#(64) temp;
+                for (int i=0; i<8; i=i+1) begin
+                  temp[i*8] = sdr_cntrl.osdr_den_n[i];
+                end
+                return temp;
+            endmethod
+        endinterface;
+
+        interface osdr_cke = interface Get
+          method ActionValue#(Bit#(1)) get;
+            return pack(sdr_cntrl.osdr_cke());
+          endmethod
+        endinterface;
+
+        ...
+        ...
+
+    endinterface;
+
+Note that the data input is quite straightforward, as is data out,
+and cke: whether 8-bit, 13-bit or 64-bit, the conversion process is
+mundane, with only Bool having to be converted to Bit#(1) with a call
+to pack.  The data-enable however is a massive hack: whilst 64 enable
+lines come in, only every 8th bit is actually utilised and passed
+through.  Whether this should be changed is a matter for debate that
+is outside of the scope of this document.
+