put versa_ecp5 below 50 mhz as a bodge-way to stop it trying

to create a DDR3 peripheral.  this then activates placing an SRAM (BRAM)
at 0x0000_0000 of size 0x8000 which can be used for a micro-test of
booting from QSPI.
and 0x8000 SRAM is much easier to simulate in icarus verilog

diff --git a/src/ls2.py b/src/ls2.py
index 1e0ca4453a331e05b85728e700e51ebed105aa6f..0d11514f931148e40cf4faef4e3c1130d2efccac 100644 (file)
--- a/src/ls2.py
+++ b/src/ls2.py
@@ -399,14 +399,15 @@ class DDR3SoC(SoC, Elaboratable):
                 self.drambone = drs(drambone)
             self._decoder.add(self.drambone.bus, addr=ddr_addr)
 
-            # additional SRAM at address if DRAM is not also at 0x0
-            # (TODO, check Flash, and HyperRAM as well)
-            if ddr_addr != 0x0:
-                sram_width = 32
-                self.bootmem = SRAMPeripheral(size=0x8000,
-                                          data_width=sram_width,
-                                          writable=True)
-                self._decoder.add(self.bootmem.bus, addr=0x0) # RAM at 0x0
+        # additional SRAM at address if DRAM is not also at 0x0
+        # (TODO, check Flash, and HyperRAM as well)
+        if ddr_pins is None or ddr_addr != 0x0:
+            print ("SRAM 0x8000 at address 0x0")
+            sram_width = 32
+            self.sram = SRAMPeripheral(size=0x8000,
+                                      data_width=sram_width,
+                                      writable=True)
+            self._decoder.add(self.sram.bus, addr=0x0) # RAM at 0x0
 
         # SPI controller
         if spi_0_pins is not None and fpga in ['sim',
@@ -474,6 +475,8 @@ class DDR3SoC(SoC, Elaboratable):
         if platform is not None and hasattr(self, "crg"):
             m.submodules.sysclk = self.crg
 
+        if hasattr(self, "sram"):
+            m.submodules.sram = self.sram
         if hasattr(self, "bootmem"):
             m.submodules.bootmem = self.bootmem
         m.submodules.syscon = self.syscon
@@ -659,7 +662,7 @@ def build_platform(fpga, firmware):
     if fpga == 'isim':
         clk_freq = 55e6 # below 50 mhz, stops DRAM being enabled
     if fpga == 'versa_ecp5':
-        clk_freq = 55e6 # crank right down to test hyperram
+        clk_freq = 45e6 # crank right down to test hyperram
     if fpga == 'versa_ecp5_85':
         # 50MHz works.  100MHz works.  55MHz does NOT work.
         # Stick with multiples of 50MHz...