[pinmux.git] / docs / AddingPeripherals.mdwn

# How to add a new peripheral

This document describes the process of adding a new peripheral to
the pinmux and auto-generator, through a worked example, adding
SDRAM.

# Creating the specifications

The tool is split into two halves that are separated by tab-separated
files.  The first step is therefore to add a function that defines
the peripheral as a python function.  That implies in turn that the
pinouts of the peripheral must be known.  Looking at the BSV code
for the SDRAM peripheral, we find its interface is defined as follows:

    interface Ifc_sdram_out;
        (*always_enabled,always_ready*)
        method Action ipad_sdr_din(Bit#(64) pad_sdr_din);
        method Bit#(9) sdram_sdio_ctrl();
        method Bit#(64) osdr_dout();
        method Bit#(8) osdr_den_n();
        method Bool osdr_cke();
        method Bool osdr_cs_n();
        method Bool osdr_ras_n ();
        method Bool osdr_cas_n ();
        method Bool osdr_we_n ();
        method Bit#(8) osdr_dqm ();
        method Bit#(2) osdr_ba ();
        method Bit#(13) osdr_addr ();
        interface Clock sdram_clk;
    endinterface

Also note further down that the code to map, for example, the 8 actual dqm
pins into a single 8-bit interface has also been auto-generated.  Generally
it is a good idea to verify that correspondingly the three data in/out/outen
interfaces have also been correctly generated.

    interface sdr = interface PeripheralSideSDR

          ...
          ...

          interface dqm = interface Put#(8)
             method Action put(Bit#(8) in);
               wrsdr_sdrdqm0 <= in[0];
               wrsdr_sdrdqm1 <= in[1];
               wrsdr_sdrdqm2 <= in[2];
               wrsdr_sdrdqm3 <= in[3];
               wrsdr_sdrdqm4 <= in[4];
               wrsdr_sdrdqm5 <= in[5];
               wrsdr_sdrdqm6 <= in[6];
               wrsdr_sdrdqm7 <= in[7];
             endmethod
           endinterface;

    endinterface;

So now we go to src/spec/pinfunctions.py and add a corresponding function
that returns a list of all of the required pin signals.  However, we note
that it is a huge number of pins so a decision is made to split it into
groups: sdram1, sdram2 and sdram3.  Firstly, sdram1, covering the base
functionality:

    def sdram1(suffix, bank):
        buspins = []
        inout = []
        for i in range(8):
            pname = "SDRDQM%d*" % i
            buspins.append(pname)
        for i in range(8):
            pname = "SDRD%d*" % i
            buspins.append(pname)
            inout.append(pname)
        for i in range(12):
            buspins.append("SDRAD%d+" % i)
        for i in range(2):
            buspins.append("SDRBA%d+" % i)
        buspins += ['SDRCKE+', 'SDRRASn+', 'SDRCASn+', 'SDRWEn+',
                    'SDRCSn0++']
        return (buspins, inout)

This function, if used on its own, would define an 8-bit SDRAM bus with
12-bit addressing. Checking off the names against the corresponding BSV
definition we find that most of them are straightforward.  Outputs
must have a "+" after the name (in the python representation), inputs
must have a "-".

However we run smack into an interesting brick-wall with the in/out pins.
In/out pins which are routed through the same IO pad need a *triplet* of
signals: one input wire, one output wire and *one direction control wire*.
Here however we find that the SDRAM controller, which is a wrapper around
the opencores SDRAM controller, has a *banked* approach to direction-control
that will need to be dealt with, later.  So we do *not* make the mistake
of adding 8 SDRDENx pins: the BSV code will need to be modified to
add 64 one-for-one enabling pins.  We do not also make the mistake of
adding separate unidirectional "in" and separate unidirectional "out" signals
under different names, as the pinmux code is a *PAD* centric tool.

The second function extends the 8-bit data bus to 64-bits, and extends
the address lines to 13-bit wide:

    def sdram3(suffix, bank):
        buspins = []
        inout = []
        for i in range(12, 13):
            buspins.append("SDRAD%d+" % i)
        for i in range(8, 64):
            pname = "SDRD%d*" % i
            buspins.append(pname)
            inout.append(pname)
        return (buspins, inout)

In this way, alternative SDRAM controller implementations can use sdram1
on its own; implementors may add "extenders" (named sdram2, sdram4) that
cover extra functionality, and, interestingly, in a pinbank scenario,
the number of pins on any given GPIO bank may be kept to a sane level.

The next phase is to add the (now supported) peripheral to the list
of pinspecs at the bottom of the file, so that it can actually be used:

    pinspec = (('IIS', i2s),
               ('MMC', emmc),
               ('FB', flexbus1),
               ('FB', flexbus2),
               ('SDR', sdram1),
               ('SDR', sdram2),
               ('SDR', sdram3), <---
               ('EINT', eint),
               ('PWM', pwm),
               ('GPIO', gpio),
               )

This gives a declaration that any time the function(s) starting with
"sdram" are used to add pins to a pinmux, it will be part of the
"SDR" peripheral.  Note that flexbus is similarly subdivided into
two groups.

Note however that due to a naming convention issue, interfaces must
be declared with names that are lexicographically unique even in
subsets of their names.  i.e two interfaces, one named "SD" which is
shorthand for SDMMC and another named "SDRAM" may *not* be added:
the first has to be the full "SDMMC" or renamed to "MMC".

# Adding the peripheral to a chip's pinmux specification

Next, we add the peripheral to an actual chip's specification.  In this
case it is to be added to i\_class, so we open src/spec/i\_class.py.  The
first thing to do is to add a single-mux (dedicated) bank of 92 pins (!)
which covers all of the 64-bit Data lines, 13 addresses and supporting
bank-selects and control lines.  It is added as Bank "D", the next
contiguous bank:

    def pinspec():
        pinbanks = {
            'A': (28, 4),
            'B': (18, 4),
            'C': (24, 1),
            'D': (92, 1), <---
        }
        fixedpins = {
            'CTRL_SYS': [

This declares the width of the pinmux to one (a dedicated peripheral
bank).  Note in passing that A and B are both 4-entry.
Next, an SDRAM interface is conveniently added to the chip's pinmux
with two simple lines of code:

    ps.gpio("", ('B', 0), 0, 0, 18)
    ps.flexbus1("", ('B', 0), 1, spec=flexspec)

    ps.flexbus2("", ('C', 0), 0)

    ps.sdram1("", ('D', 0), 0)   <--
    ps.sdram3("", ('D', 35), 0)  <--

Note that the first argument is blank, indicating that this is the only
SDRAM interface to be added.  If more than one SDRAM interface is desired
they would be numbered from 0 and identified by their suffix.  The second
argument is a tuple of (Bank Name, Bank Row Number), and the third argument
is the pinmux column (which in this case must be zero).

At the top level the following command is then run:

    $ python src/pinmux_generator.py -o i_class -s i_class

The output may be found in the ./i\_class subdirectory, and it is worth
examining the i\_class.mdwn file.  A table named "Bank D" will have been
created and it is worth just showing the first few entries here:

| Pin | Mux0        | Mux1        | Mux2        | Mux3        |
| --- | ----------- | ----------- | ----------- | ----------- |
|  70 | D SDR_SDRDQM0 |
|  71 | D SDR_SDRDQM1 |
|  72 | D SDR_SDRDQM2 |
|  73 | D SDR_SDRDQM3 |
|  74 | D SDR_SDRDQM4 |
|  75 | D SDR_SDRDQM5 |
|  76 | D SDR_SDRDQM6 |
|  77 | D SDR_SDRDQM7 |
|  78 | D SDR_SDRD0 |
|  79 | D SDR_SDRD1 |
|  80 | D SDR_SDRD2 |
|  81 | D SDR_SDRD3 |
|  82 | D SDR_SDRD4 |
|  83 | D SDR_SDRD5 |
|  84 | D SDR_SDRD6 |
|  85 | D SDR_SDRD7 |
|  86 | D SDR_SDRAD0 |
|  87 | D SDR_SDRAD1 |

Returning to the definition of sdram1 and sdram3, this table clearly
corresponds to the functions in src/spec/pinfunctions.py which is
exactly what we want.  It is however extremely important to verify.

Lastly, the peripheral is a "fast" peripheral, i.e. it must not
be added to the "slow" peripherals AXI4-Lite Bus, so must be added
to the list of "fast" peripherals, here:

    ps = PinSpec(pinbanks, fixedpins, function_names,
                 ['lcd', 'jtag', 'fb', 'sdr'])        <--

    # Bank A, 0-27
    ps.gpio("", ('A', 0), 0, 0, 28)

This basically concludes the first stage of adding a peripheral to
the pinmux / autogenerator tool.  It allows peripherals to be assessed
for viability prior to actually committing the engineering resources
to their deployment.

# Adding the code auto-generators.

With the specification now created and well-defined (and now including
the SDRAM interface), the next completely separate phase is to auto-generate
the code that will drop an SDRAM instance onto the fabric of the SoC.

This particular peripheral is classified as a "Fast Bus" peripheral.
"Slow" peripherals will need to be the specific topic of an alternative
document, however the principles are the same.

The first requirement is that the pins from the peripheral side be connected
through to IO cells.  This can be verified by running the pinmux code
generator (to activate "default" behaviour), just to see what happens:

    $ python src/pinmux_generator.py -o i_class

Files are auto-generated in ./i\_class/bsv\_src and it is recommended
to examine the pinmux.bsv file in an editor, and search for occurrences
of the string "sdrd63".  It can clearly be seen that an interface
named "PeripheralSideSDR" has been auto-generated:

    // interface declaration between SDR and pinmux
    (*always_ready,always_enabled*)
    interface PeripheralSideSDR;
      interface Put#(Bit#(1)) sdrdqm0;
      interface Put#(Bit#(1)) sdrdqm1;
      interface Put#(Bit#(1)) sdrdqm2;
      interface Put#(Bit#(1)) sdrdqm3;
      interface Put#(Bit#(1)) sdrdqm4;
      interface Put#(Bit#(1)) sdrdqm5;
      interface Put#(Bit#(1)) sdrdqm6;
      interface Put#(Bit#(1)) sdrdqm7;
      interface Put#(Bit#(1)) sdrd0_out;
      interface Put#(Bit#(1)) sdrd0_outen;
      interface Get#(Bit#(1)) sdrd0_in;
      ....
      ....
    endinterface

Note that for the data lines, that where in the sdram1 specification function
the signals were named "SDRDn+, out, out-enable *and* in interfaces/methods
have been created, as these will be *directly* connected to the I/O pads.

Further down the file we see the *actual* connection to the I/O pad (cell).
An example:

    // --------------------
    // ----- cell 161 -----

    // output muxer for cell idx 161
    cell161_mux_out=
        wrsdr_sdrd63_out;

    // outen muxer for cell idx 161
    cell161_mux_outen=
        wrsdr_sdrd63_outen; // bi-directional

    // priority-in-muxer for cell idx 161

    rule assign_wrsdr_sdrd63_in_on_cell161;
        wrsdr_sdrd63_in<=cell161_mux_in;
    endrule

Here, given that this is a "dedicated" cell (with no muxing), we have
*direct* assignment of all three signals (in, out, outen).  2-way, 3-way
and 4-way muxing creates the required priority-muxing for inputs and
straight-muxing for outputs, however in this instance, a deliberate
pragmatic decision is being taken not to put 92 pins of 133mhz+ signalling
through muxing.

## Making the peripheral a "MultiBus" peripheral

The sheer number of signals coming out of PeripheralSideSDR is so unwieldy
that something has to be done.  We therefore create a "MultiBus" interface
such that the pinmux knows which pins are grouped together by name.
This is done in src/bsv/interface\_decl.py.

The MultiBus code is quite sophisticated, in that buses can be identified
by pattern, and removed one by one.  The *remaining* pins are left behind
as individual single-bit pins.  Starting from a copy of InterfaceFlexBus
as the most similar code, a cut/paste copy is taken and the new class
InterfaceSDRAM created:

    class InterfaceSDRAM(InterfaceMultiBus, Interface):

        def __init__(self, ifacename, pinspecs, ganged=None, single=False):
            Interface.__init__(self, ifacename, pinspecs, ganged, single)
            InterfaceMultiBus.__init__(self, self.pins)
            self.add_bus(False, ['dqm', None, None],
                         "Bit#({0})", "sdrdqm")
            self.add_bus(True, ['d_out', 'd_out_en', 'd_in'],
                         "Bit#({0})", "sdrd")
            self.add_bus(False, ['ad', None, None],
                         "Bit#({0})", "sdrad")
            self.add_bus(False, ['ba', None, None],
                         "Bit#({0})", "sdrba")

        def ifacedef2(self, *args):
            return InterfaceMultiBus.ifacedef2(self, *args)

Here, annoyingly, the data bus is a mess, requiring identification of
the three separate names for in, out and outen.  The prefix "sdrd" is however
unique and obvious in its purpose: anything beginning with "sdrd" is
treated as a multi-bit bus, and a template for declaring a BSV type is
given that is automatically passed the numerical quantity of pins detected
that start with the word "sdrd".

Note that it is critical to lexicographically identify pins correctly,
so sdrdqm is done **before** sdrd.

Once the buses have been identified the peripheral can be added into
class Interfaces:

    class Interfaces(InterfacesBase, PeripheralInterfaces):
        """ contains a list of interface definitions
        """

        def __init__(self, pth=None):
            InterfacesBase.__init__(self, Interface, pth,
                                    {'gpio': InterfaceGPIO,
                                     'fb': InterfaceFlexBus,
                                     'sdr': InterfaceSDRAM,  <--

Running the tool again results in a much smaller, tidier output
that will be a lot less work, later.  Note the automatic inclusion of
the correct length multi-bit interfaces.  d-out/in/out-en is identified
as 64-bit, ad is identified as 13-bit, ba as 2 and dqm as 8.

      // interface declaration between SDR and pinmux
      (*always_ready,always_enabled*)
      interface PeripheralSideSDR;
          interface Put#(Bit#(1)) sdrcke;
          interface Put#(Bit#(1)) sdrrasn;
          interface Put#(Bit#(1)) sdrcasn;
          interface Put#(Bit#(1)) sdrwen;
          interface Put#(Bit#(1)) sdrcsn0;

          interface Put#(Bit#(8)) dqm;
          interface Put#(Bit#(64)) d_out;
          interface Put#(Bit#(64)) d_out_en;
          interface Get#(Bit#(64)) d_in;
          interface Put#(Bit#(13)) ad;
          interface Put#(Bit#(2)) ba;

      endinterface

## Adding the peripheral

In examining the slow\_peripherals.bsv file, there should at this stage
be no sign of an SDRAM peripheral having been added, at all.  This is
because it is missing from the peripheral\_gen side of the tool.

However, as the slow\_peripherals module takes care of the IO cells
(because it contains a declared and configured instance of the pinmux
package), signals from the pinmux PeripheralSideSDR instance need
to be passed *through* the slow peripherals module as an external
interface.  This will happen automatically once a code-generator class
is added.

So first, we must identify the nearest similar class.  FlexBus looks
like a good candidate, so we take a copy of src/bsv/peripheral\_gen/flexbus.py
called sdram.py.  The simplest next step is to global/search/replace
"flexbus" with "sdram", and for peripheral instance declaration replace
"fb" with "sdr".  At this phase, despite knowing that it will
auto-generate the wrong code, we add it as a "supported" peripheral
at the bottom of src/bsv/peripheral\_gen/base.py, in the "PFactory"
(Peripheral Factory) class:

    from gpio import gpio
    from rgbttl import rgbttl
    from flexbus import flexbus
    from sdram import sdram       <--

    for k, v in {'uart': uart,
                 'rs232': rs232,
                 'sdr': sdram,
                 'twi': twi,
                 'quart': quart,

Note that the name "SDR" matches with the prefix used in the pinspec
declaration, back in src/spec/pinfunctions.py, except lower-cased.  Once this
is done, and the auto-generation tool re-run, examining the
slow\_peripherals.bsv file again shows the following (correct) and only
the following (correct) additions:

    method Bit#(1) quart0_intr;
    method Bit#(1) quart1_intr;
    interface GPIO_config#(28) pad_configa;
    interface PeripheralSideSDR sdr0;        <--
    interface PeripheralSideFB fb0;

    ....
    ....
    interface iocell_side=pinmux.iocell_side;
    interface sdr0 = pinmux.peripheral_side.sdr;   <--
    interface fb0 = pinmux.peripheral_side.fb;

These automatically-generated declarations are sufficient to "pass through"
the SDRAM "Peripheral Side", which as we know from examination of the code
is directly connected to the relevant IO pad cells, so that the *actual*
peripheral may be declared in the "fast" fabric and connected up to the
relevant and required "fast" bus.

## Connecting in the fabric

Now we can begin the process of systematically inserting the correct
"voodoo magic" incantations that, as far as this auto-generator tool is
concerned, are just bits of ASCII text.  In this particular instance, an
SDRAM peripheral happened to already be *in* the SoC's BSV source code,
such that the process of adding it to the tool is primarily one of
*conversion*.

**Please note that it is NOT recommended to do two tasks at once.
It is strongly recommended to add any new peripheral to a pre-existing
verified project, manually, by hand, and ONLY then to carry out a
conversion process to have this tool understand how to auto-generate
the fabric**

So examining the i\_class socgen.bsv file, we also open up
src/bsv/bsv\_lib/soc\_template.bsv in side-by-side windows of maximum
80 characters in width each, and *respect the coding convention for
this exact purpose*, can easily fit two such windows side-by-side
*as well as* a third containing the source code files that turn that
same template into its corresponding output.

We can now begin by searching for strings "SDRAM" and "sdr" in both
the template and the auto-generated socgen.bsv file.  The first such
encounter is the import, in the template:

    `ifdef BOOTROM
        import BootRom          ::*;
    `endif
    `ifdef SDRAM                         <-- xxxx
        import sdr_top           :: *;   <-- xxxx
    `endif                               <-- xxxx
    `ifdef BRAM

This we can **remove**, and drop the corresponding code-fragment into
the sdram slowimport function:

    class sdram(PBase):

        def slowimport(self):
            return "import sdr_top::*;"  <--

        def num_axi_regs32(self):

Now we re-run the auto-generator tool and confirm that, indeed, the
ifdef'd code is gone and replaced with an unconditional import:

    import mqspi              :: *;
    import sdr_top::*;                  <--
    import Uart_bs         :: *;
    import RS232_modified::*;
    import mspi              :: *;

Progress!  Next, we examine the instance declaration clause.  Remember
that we cut/paste the flexbus class, so we are expecting to find code
that declares the sdr0 instance as a FlexBus peripheral.  We are
also looking for the hand-created code that is to be *replaced*.  Sure enough:

    AXI4_Slave_to_FlexBus_Master_Xactor_IFC #(`PADDR, `DATA, `USERSPACE)
            sdr0 <- mkAXI4_Slave_to_FlexBus_Master_Xactor;               <--
    AXI4_Slave_to_FlexBus_Master_Xactor_IFC #(`PADDR, `DATA, `USERSPACE)
            fb0 <- mkAXI4_Slave_to_FlexBus_Master_Xactor;
    ...
    ...
    `ifdef BOOTROM
        BootRom_IFC bootrom <-mkBootRom;
    `endif
    `ifdef SDRAM                                       <--
        Ifc_sdr_slave sdram<- mksdr_axi4_slave(clk0);  <--
    `endif                                             <--

So, the mksdr\_axi4\_slave call we *remove* from the template and cut/paste
it into the sdram class's mkfast_peripheral function, making sure to
substitute the hard-coded instance name "sdram" with a python-formatted
template that can insert numerical instance identifiers, should it ever
be desired that there be more than one SDRAM peripheral put into a chip:

class sdram(PBase):

    ...
    ...
    def mkfast_peripheral(self):
        return "Ifc_sdr_slave sdr{0} <- mksdr_axi4_slave(clk0);"

Re-run the tool and check that the correct-looking code has been created:

    Ifc_sdr_slave sdr0 <- mksdr_axi4_slave(clk0);                        <--
    AXI4_Slave_to_FlexBus_Master_Xactor_IFC #(`PADDR, `DATA, `USERSPACE)
            fb0 <- mkAXI4_Slave_to_FlexBus_Master_Xactor;
    Ifc_rgbttl_dummy lcd0 <-  mkrgbttl_dummy();

The next thing to do: searching for the string "sdram\_out" shows that the
original hand-generated code contains (contained) a declaration of the
SDRAM Interface, presumably to which, when compiling to run on an FPGA,
the SDRAM interface would be connected at the top level.  Through this
interface, connections would be done *by hand* to the IO pads, whereas
now they are to be connected *automatically* (on the peripheral side)
to the IO pads in the pinmux.  However, at the time of writing this is
not fully understood by the author, so the fastifdecl and extfastifinstance
functions are modified to generate the correct output but the code is
*commented out*

    def extfastifinstance(self, name, count):
        return "// TODO" + self._extifinstance(name, count, "_out", "", True,
                                   ".if_sdram_out")

    def fastifdecl(self, name, count):
        return "// (*always_ready*) interface " + \
                "Ifc_sdram_out sdr{0}_out;".format(count)

Also the corresponding (old) manual declarations of sdram\_out
removed from the template:

    `ifdef SDRAM                                            <-- xxxx
        (*always_ready*) interface Ifc_sdram_out sdram_out; <-- xxxx
    `endif                                                  <-- xxxx
    ...
    ...
    `ifdef SDRAM                                  <--- xxxx
        interface sdram_out=sdram.ifc_sdram_out;  <--- xxxx
    `endif                                        <--- xxxx

Next, again searching for signs of the "hand-written" code, we encounter
the fabric connectivity, which wires the SDRAM to the AXI4.  We note however
that there is not just one AXI slave device but *two*: one for the SDRAM
itself and one for *configuring* the SDRAM.  We therefore need to be
quite careful about assigning these, as will be subsequently explained.
First however, the two AXI4 slave interfaces of this peripheral are
declared:

    class sdram(PBase):

        ...
        ...
        def _mk_connection(self, name=None, count=0):
            return ["sdr{0}.axi4_slave_sdram",
                    "sdr{0}.axi4_slave_cntrl_reg"]

Note that, again, in case multiple instances are ever to be added, the
python "format" string "{0}" is inserted so that it can be substituted
with the numerical identifier suffix.  Also note that the order
of declaration of these two AXI4 slave is **important**.

Re-running the auto-generator tool, we note the following output has
been created, and match it against the corresponding hand-generated (old)
code:

    `ifdef SDRAM
            mkConnection (fabric.v_to_slaves
                              [fromInteger(valueOf(Sdram_slave_num))],
                              sdram.axi4_slave_sdram); // 
            mkConnection (fabric.v_to_slaves
                              [fromInteger(valueOf(Sdram_cfg_slave_num))],
                              sdram.axi4_slave_cntrl_reg); // 
    `endif

    // fabric connections
    mkConnection (fabric.v_to_slaves
                [fromInteger(valueOf(SDR0_fastslave_num))],
                sdr0.axi4_slave_sdram);
    mkConnection (fabric.v_to_slaves
                [fromInteger(valueOf(SDR0_fastslave_num))],
                sdr0.axi4_slave_cntrl_reg);

Immediately we can spot an issue: whilst the correctly-named slave(s) have
been added, they have been added with the *same* fabric slave index.  This
is unsatisfactory and needs resolving.

Here we need to explain a bit more about what is going on.  The fabric
on an AXI4 Bus is allocated numerical slave numbers, and each slave is
also allocated a memory-mapped region that must be resolved in a bi-directional
fashion.  i.e whenever a particular memory region is accessed, the AXI
slave peripheral responsible for dealing with it **must** be correctly
identified.  So this requires some further crucial information, which is
the size of the region that is to be allocated to each slave device.  Later
this will be extended to being part of the specification, but for now
it is auto-allocated based on the size.  As a huge hack, it is allocated
in 32-bit chunks, as follows:

class sdram(PBase):

    def num_axi_regs32(self):
        return [0x400000,  # defines an entire memory range (hack...)
                12]        # defines the number of configuration regs

So after running the autogenerator again, to confirm that this has
generated the correct code, we examine several files, starting with
fast\+memory\_map.bsv:

    /*====== Fast peripherals Memory Map ======= */
    `define SDR0_0_Base 'h50000000
    `define SDR0_0_End  'h5FFFFFFF // 4194304 32-bit regs
    `define SDR0_1_Base 'h60000000
    `define SDR0_1_End  'h600002FF // 12 32-bit regs

This looks slightly awkward (and in need of an external specification
section for addresses) but is fine: the range is 1GB for the main
map and covers 12 32-bit registers for the SDR Config map.
Next we note the slave numbering:

    typedef 0 SDR0_0__fastslave_num;
    typedef 1 SDR0_1__fastslave_num;
    typedef 2 FB0_fastslave_num;
    typedef 3 LCD0_fastslave_num;
    typedef 3 LastGen_fastslave_num;
    typedef  TAdd#(LastGen_fastslave_num,1)      Sdram_slave_num;
    typedef  TAdd#(Sdram_slave_num   ,`ifdef SDRAM      1 `else 0 `endif )
                          Sdram_cfg_slave_num;

Again this looks reasonable and we may subsequently (carefully! noting
the use of the TAdd# chain!) remove the #define for Sdram\_cfg\_slave\_num.
The next phase is to examine the fn\_addr\_to\_fastslave\_num function,
where we note that there were *two* hand-created sections previously,
now joined by two *auto-generated* sections:

    function Tuple2 #(Bool, Bit#(TLog#(Num_Fast_Slaves)))
                    fn_addr_to_fastslave_num  (Bit#(`PADDR) addr);

      if(addr>=`SDRAMMemBase && addr<=`SDRAMMemEnd)
          return tuple2(True,fromInteger(valueOf(Sdram_slave_num)));  <--
      else if(addr>=`DebugBase && addr<=`DebugEnd)
          return tuple2(True,fromInteger(valueOf(Debug_slave_num)));  <--
      `ifdef SDRAM
          else if(addr>=`SDRAMCfgBase && addr<=`SDRAMCfgEnd )
              return tuple2(True,fromInteger(valueOf(Sdram_cfg_slave_num)));
      `endif

      ...
      ...
      if(addr>=`SDR0_0_Base && addr<=`SDR0_0_End)                         <--
          return tuple2(True,fromInteger(valueOf(SDR0_0__fastslave_num)));
      else
      if(addr>=`SDR0_1_Base && addr<=`SDR0_1_End)                         <--
          return tuple2(True,fromInteger(valueOf(SDR0_1__fastslave_num)));
      else
      if(addr>=`FB0Base && addr<=`FB0End)

Now, here is where, in a slightly unusual unique set of circumstances, we
cannot just remove all instances of this address / typedef from the template
code.  Looking in the shakti-core repository's src/lib/MemoryMap.bsv file,
the SDRAMMemBase macro is utilise in the is\_IO\_Addr function.  So as a
really bad hack, which will need to be properly resolved, whilst the
hand-generated sections from fast\_tuple2\_template.bsv are removed,
and the corresponding (now redundant) defines in src/core/core\_parameters.bsv
are commented out, some temporary typedefs to deal with the name change are
also added:

    `define SDRAMMemBase SDR0_0_Base
    `define SDRAMMemEnd SDR0_0_End

This needs to be addressed (pun intended) including being able to specify
the name(s) of the configuration parameters, as well as specifying which
memory map range they must be added to.

Now however finally, after carefully comparing the hard-coded fabric
connections to what was formerly named sdram, we may remove the mkConnections
that drop sdram.axi4\_slave\_sdram and its associated cntrl reg from
the soc\_template.bsv file.

## Connecting up the pins

We are still not done!  It is however worth pointing out that if this peripheral
were not wired into the pinmux, we would in fact be finished.  However there
is a task that (previously having been left to outside tools) now needs to
be specified, which is to connect the sdram's pins, declared in this
instance in Ifc\_sdram\_out, and the PeripheralSideSDR instance that
was kindly / strategically / thoughtfully / absolutely-necessarily exported
from slow\_peripherals for exactly this purpose.

Recall earlier that we took a cut/paste copy of the flexbus.py code.  If
we now examine socgen.bsv we find that it contains connections to pins
that match the FlexBus specification, not SDRAM.  So, returning to the
declaration of the Ifc\_sdram\_out interface, we first identify the
single-bit output-only pins, and add a mapping table between them:

    class sdram(PBase):

        def pinname_out(self, pname):
            return {'sdrwen': 'ifc_sdram_out.osdr_we_n',
                    'sdrcsn0': 'ifc_sdram_out.osdr_cs_n',
                    'sdrcke': 'ifc_sdram_out.osdr_cke',
                    'sdrrasn': 'ifc_sdram_out.osdr_ras_n',
                    'sdrcasn': 'ifc_sdram_out.osdr_cas_n',
                    }.get(pname, '')

Re-running the tool confirms that the relevant mkConnections are generated:

    //sdr {'action': True, 'type': 'out', 'name': 'sdrcke'}
    mkConnection(slow_peripherals.sdr0.sdrcke,
                sdr0_sdrcke_sync.get);
    mkConnection(sdr0_sdrcke_sync.put,
                sdr0.ifc_sdram_out.osdr_cke);
    //sdr {'action': True, 'type': 'out', 'name': 'sdrrasn'}
    mkConnection(slow_peripherals.sdr0.sdrrasn,
                sdr0_sdrrasn_sync.get);
    mkConnection(sdr0_sdrrasn_sync.put,
                sdr0.ifc_sdram_out.osdr_ras_n);

Next, the multi-value entries are tackled (both in and out).  At present
the code is messy, as it does not automatically detect the multiple numerical
declarations, nor that the entries are sometimes inout (in, out, outen),
so it is *presently* done by hand:

    class sdram(PBase):

        def _mk_pincon(self, name, count, typ):
            ret = [PBase._mk_pincon(self, name, count, typ)]
            assert typ == 'fast' # TODO slow?
            for pname, stype, ptype in [
                ('dqm', 'osdr_dqm', 'out'),
                ('ba', 'osdr_ba', 'out'),
                ('ad', 'osdr_addr', 'out'),
                ('d_out', 'osdr_dout', 'out'),
                ('d_in', 'ipad_sdr_din', 'in'),
                ('d_out_en', 'osdr_den_n', 'out'),
            ]:
                ret.append(self._mk_vpincon(name, count, typ, ptype, pname,
                                            "ifc_sdram_out.{0}".format(stype)))

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.