Slighty extended, added own CRG

Author: riktw

sipeed_tang_nano_9k.py

@@ -1,47 +1,75 @@
 #!/usr/bin/env python3
 
 #
-# Minimum tang nano 9k example. Should work with most board with minimal changes 
+# This file is part of LiteX-Boards.
 #
+# Copyright (c) 2022 Icenowy Zheng <icenowy@aosc.io>
+# SPDX-License-Identifier: BSD-2-Clause
 
 import os
 from migen import *
 
 from litex.gen import *
 
-import sipeed_tang_nano_9K_platform  # It can be imported from litex_boards of course, but this way changes can be kept in the same repo
+import sipeed_tang_nano_9K_platform
 
-from litex.build.io import CRG
+from litex.soc.cores.clock.gowin_gw1n import GW1NPLL
 from litex.soc.integration.soc_core import *
 from litex.soc.integration.soc import SoCRegion
 from litex.soc.integration.builder import *
 
 kB = 1024
 mB = 1024*kB
 
+# CRG stands for Clock Reset Generator
+# Here at least a clock and reset are added, and any PLLs. 
+# In this case a PLL with the same in and output frequency and a user button is used as reset for the PLL. 
+class _CRG(LiteXModule):
+    def __init__(self, platform, sys_clk_freq, with_video_pll=False):
+        self.rst    = Signal()
+        self.cd_sys = ClockDomain()
+
+        # Clk / Rst
+        clk27 = platform.request("clk27")
+        rst_n = platform.request("user_btn", 0)
+
+        # PLL
+        self.pll = pll = GW1NPLL(devicename=platform.devicename, device=platform.device)
+        self.comb += pll.reset.eq(~rst_n)
+        pll.register_clkin(clk27, 27e6)
+        pll.create_clkout(self.cd_sys, sys_clk_freq)
+
 # BaseSoC ------------------------------------------------------------------------------------------
 class BaseSoC(SoCCore):
-    def __init__(self, **kwargs):
+    def __init__(self, sys_clk_freq=27e6, bios_flash_offset=0x0,
+        **kwargs):
         platform = sipeed_tang_nano_9K_platform.Platform()
 
-        sys_clk_freq = int(1e9/platform.default_clk_period)
-
-        # CRG --------------------------------------------------------------------------------------
-        self.crg = CRG(platform.request(platform.default_clk_name))
+        # Notice the custom CRG here, _CRG instead of CRG
+        self.crg = _CRG(platform, sys_clk_freq)
 
         # SoCCore ----------------------------------------------------------------------------------
-        kwargs["integrated_rom_size"] = 64*kB  
+        kwargs["integrated_rom_size"] = 64*kB
         kwargs["integrated_sram_size"] = 8*kB
-        SoCCore.__init__(self, platform, sys_clk_freq, ident="Tiny LiteX SoC on Tang Nano 9K", **kwargs)
+        SoCCore.__init__(self, platform, sys_clk_freq, ident="Still tiny LiteX SoC on Tang Nano 9K", **kwargs)
+
 
 # Build --------------------------------------------------------------------------------------------
+# Some extra arguments got added, sys-clk-freq to change the CPU frequency, we got a PLL after all. and a bios flash offset
+# Try --sys-clk-freq=54e6 to run it at twice the clock speed!
 def main():
     from litex.build.parser import LiteXArgumentParser
-    parser = LiteXArgumentParser(platform=sipeed_tang_nano_9K_platform.Platform, description="Tiny LiteX SoC on Tang Nano 9K.")
+    parser = LiteXArgumentParser(platform=sipeed_tang_nano_9K_platform.Platform, description="Still tiny LiteX SoC on Tang Nano 9K.")
     parser.add_target_argument("--flash",                action="store_true",      help="Flash Bitstream.")
+    parser.add_target_argument("--sys-clk-freq",         default=27e6, type=float, help="System clock frequency.")
+    parser.add_target_argument("--bios-flash-offset",    default="0x0",            help="BIOS offset in SPI Flash.")
     args = parser.parse_args()
 
-    soc = BaseSoC( **parser.soc_argdict)
+    soc = BaseSoC(
+        sys_clk_freq        = args.sys_clk_freq,
+        bios_flash_offset   = int(args.bios_flash_offset, 0),
+        **parser.soc_argdict
+    )
 
     builder = Builder(soc, **parser.builder_argdict)
     if args.build:
@@ -54,7 +82,7 @@ def main():
     if args.flash:
         prog = soc.platform.create_programmer("openfpgaloader")
         prog.flash(0, builder.get_bitstream_filename(mode="flash", ext=".fs")) # FIXME
-        prog.flash(0, builder.get_bios_filename(), external=True)
+        prog.flash(int(args.bios_flash_offset, 0), builder.get_bios_filename(), external=True)
 
 if __name__ == "__main__":
     main()