add beginnings of syscon bus peripheral

diff --git a/src/soc/bus/syscon.py b/src/soc/bus/syscon.py
new file mode 100644 (file)
index 0000000..602c780
--- /dev/null
+++ b/src/soc/bus/syscon.py
@@ -0,0 +1,118 @@
+#!/usr/bin/env python3
+#
+# SPDX-License-Identifier: LGPLv3+
+# Copyright (C) 2022 Luke Kenneth Casson Leighton <lkcl@lkcl.net>
+# Sponsored by NLnet and NGI POINTER under EU Grants 871528 and 957073
+# Part of the Libre-SOC Project.
+#
+# this is a System Console peripheral compatible with microwatt
+# https://github.com/antonblanchard/microwatt/blob/master/syscon.vhdl
+
+from nmigen import (Elaboratable, Cat, Module, Signal)
+from nmigen.cli import rtlil, verilog
+
+from lambdasoc.periph import Peripheral
+
+__all__ = ["MicrowattSYSCON"]
+
+
+class MicrowattSYSCON(Peripheral, Elaboratable):
+    """Microwatt-compatible (Sys)tem (Con)figuration module
+    """
+
+    def __init__(self, *, sys_clk_freq=100e6,
+                          has_uart=True,
+                          uart_is_16550=True
+                          ):
+        super().__init__(name="syscon")
+        self.sys_clk_freq = sys_clk_freq
+        self.has_uart = has_uart
+        self.uart_is_16550 = uart_is_16550
+
+        # System control ports
+        self.dram_at_0 = Signal()
+        self.core_reset = Signal()
+        self.soc_reset = Signal()
+
+        # set up a CSR Bank and associated bridge. has to be in this order
+        # (declare bank, declare bridge) for some unknown reason.
+        # (r)ead regs will have a r_stb and r_data Record entry
+        # (w)rite regs will have a w_stb and w_data Record entry
+        bank = self.csr_bank()
+        self._reg_sig_r       = bank.csr(64, "r") # signature
+        self._reg_info_r      = bank.csr(64, "r") # info
+        self._bram_info_r     = bank.csr(64, "r") # bram info
+        self._dram_info_r     = bank.csr(64, "r") # dram info
+        self._clk_info_r      = bank.csr(64, "r") # clock frequency
+        self._ctrl_info_r     = bank.csr(64, "rw") # control info
+        self._dram_init_r     = bank.csr(64, "r") # dram initialisation info
+        self._spiflash_info_r = bank.csr(64, "r") # spi flash info
+        self._uart0_info_r    = bank.csr(64, "r") # UART0 info (baud etc.)
+        self._uart1_info_r    = bank.csr(64, "r") # UART1 info (baud etc.)
+        self._bram_bootaddr_r = bank.csr(64, "r") # BRAM boot address
+
+        # bridge the above-created CSRs over wishbone.  ordering and size
+        # above mattered, the bridge automatically packs them together
+        # as memory-addressable "things" for us
+        self._bridge = self.bridge(data_width=32, granularity=8, alignment=3)
+        self.bus = self._bridge.bus
+
+    def elaborate(self, platform):
+        m = Module()
+        comb, sync = m.d.comb, m.d.comb
+        m.submodules.bridge = self._bridge
+
+        # enter data into the CSRs. r_data can be left live all the time,
+        # w_data obviously has to be set only when w_stb triggers.
+
+        # identifying signature
+        comb += self._reg_sig_r.r_data.eq(0xf00daa5500010001)
+
+        # system clock rate (hz)
+        comb += self._clk_info_r.r_data.eq(int(self.sys_clk_freq)) # in hz
+
+        # uart peripheral clock rate, currently assumed to be system clock
+        # 0 ..31  : UART clock freq (in HZ)
+        #     32  : UART is 16550 (otherwise pp)
+        if self.has_uart:
+            comb += self._uart0_info_r.r_data[0:32].eq(int(self.sys_clk_freq))
+            comb += self._uart0_info_r.r_data[32].eq(1)
+
+        # system control
+        sysctrl = Cat(self.dram_at_0, self.core_reset, self.soc_reset)
+        with m.If(self._ctrl_info_r.w_stb):
+            sync += sysctrl.eq(self._ctrl_info_r.w_data)
+        comb += self._ctrl_info_r.r_data.eq(sysctrl)
+
+        return m
+
+
+def create_ilang(dut, ports, test_name):
+    vl = rtlil.convert(dut, name=test_name, ports=ports)
+    with open("%s.il" % test_name, "w") as f:
+        f.write(vl)
+
+def create_verilog(dut, ports, test_name):
+    vl = verilog.convert(dut, name=test_name, ports=ports)
+    with open("%s.v" % test_name, "w") as f:
+        f.write(vl)
+
+
+if __name__ == "__main__":
+    from nmigen_soc import wishbone
+    class QuickDemo(Elaboratable):
+        def elaborate(self, platform):
+            m = Module()
+            arbiter = wishbone.Arbiter(addr_width=30, data_width=32,
+                                       granularity=8)
+            decoder = wishbone.Decoder(addr_width=30, data_width=32, 
+                                       granularity=8)
+            m.submodules.syscon = syscon = MicrowattSYSCON()
+            m.submodules.decoder = decoder
+            m.submodules.arbiter = arbiter
+            decoder.add(syscon.bus, addr=0xc0000000)
+            m.d.comb += arbiter.bus.connect(decoder.bus)
+            return m
+    m = QuickDemo()
+    create_ilang(m, None, "syscondemo")
+