From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Sun, 2 Jan 2022 15:34:38 +0000 (+0000)
Subject: rrright.  ok.  these modifications to sdram_init allow it
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=9b5bd2d757966b696dddb1d0ec9dd1f953f38983;p=microwatt.git

rrright.  ok.  these modifications to sdram_init allow it
to be compiled and used stand-alone.  sdram initialisation is disabled.
the general idea here is to make this a useful mini-BIOS bootloader,
focussing initially on verilator start-up.  to that end, the first
addition is a SYS_REG_BRAM_BOOTADDR addition to syscon which is the
location where the chain-loading continues (if SPI and SDRAM are not
available, where SDRAM is definitely out at this point)
---

diff --git a/include/microwatt_soc.h b/include/microwatt_soc.h
index a224d74..989721b 100644
--- a/include/microwatt_soc.h
+++ b/include/microwatt_soc.h
@@ -18,7 +18,11 @@
 #define LETH_CSR_BASE	0xc8020000  /* LiteEth CSR registers */
 #define LETH_SRAM_BASE	0xc8030000  /* LiteEth MMIO space */
 #define SPI_FLASH_BASE  0xf0000000  /* SPI Flash memory map */
+#ifdef STANDALONE_MINI_BIOS
+#define DRAM_INIT_BASE  0x00000000  /* alternative, for verilator simulation */
+#else
 #define DRAM_INIT_BASE  0xff000000  /* Internal DRAM init firmware */
+#endif
 
 /*
  * Interrupt numbers
@@ -56,6 +60,7 @@
 #define SYS_REG_UART0_INFO		0x40
 #define SYS_REG_UART1_INFO		0x48
 #define   SYS_REG_UART_IS_16550			(1ull << 32)
+#define SYS_REG_BRAM_BOOTADDR		0x50
 
 
 /*
diff --git a/litedram/gen-src/sdram_init/Makefile b/litedram/gen-src/sdram_init/Makefile
index 2e622d4..8311759 100644
--- a/litedram/gen-src/sdram_init/Makefile
+++ b/litedram/gen-src/sdram_init/Makefile
@@ -1,12 +1,28 @@
 #### Directories
 
-include variables.mak
+# check for variables.mak and if not, allow stand-alone BIOS to be compiled
+# (disables SDRAM)
+ifeq ("$(wildcard variables.mak)","")
+    include variables.mak
+    NO_SDRAM=
+else
+    BUILD_DIR=.
+    SRC_DIR=.
+    GENINC_DIR=.
+    NO_SDRAM=true
+    EXTRA_CFLAGS=-DSTANDALONE_MINI_BIOS
+endif
+
 OBJ = $(BUILD_DIR)/obj
 
 LXINC_DIR=$(LXSRC_DIR)/include
 
 PROGRAM = sdram_init
+ifeq ($(NO_SDRAM), true)
+OBJECTS = $(OBJ)/head.o $(OBJ)/main.o $(OBJ)/console.o
+else
 OBJECTS = $(OBJ)/head.o $(OBJ)/main.o $(OBJ)/sdram.o $(OBJ)/memtest.o $(OBJ)/console.o
+endif
 
 #### Compiler
 
@@ -32,7 +48,7 @@ CPPFLAGS += -I$(GENINC_DIR) -I$(SRC_DIR)/include -I$(SRC_DIR)/../../../include -
 CPPFLAGS += -I$(LXSRC_DIR) -I$(LXINC_DIR) -I$(LXINC_DIR)/base -I$(LXSRC_DIR)/liblitedram
 
 CPPFLAGS += -isystem $(shell $(CC) -print-file-name=include)
-CFLAGS = -Os -g -Wall -std=c99 -m64 -mabi=elfv2 -msoft-float -mno-string -mno-multiple -mno-vsx -mno-altivec -mlittle-endian -fno-stack-protector -mstrict-align -ffreestanding -fdata-sections -ffunction-sections -fno-delete-null-pointer-checks 
+CFLAGS = -Os -g -Wall -std=c99 -m64 -mabi=elfv2 -msoft-float -mno-string -mno-multiple -mno-vsx -mno-altivec -mlittle-endian -fno-stack-protector -mstrict-align -ffreestanding -fdata-sections -ffunction-sections -fno-delete-null-pointer-checks
 ASFLAGS = $(CPPFLAGS) $(CFLAGS)
 LDFLAGS = -static -nostdlib -T $(OBJ)/$(PROGRAM).lds --gc-sections
 
diff --git a/litedram/gen-src/sdram_init/head.S b/litedram/gen-src/sdram_init/head.S
index 2e9f053..a008231 100644
--- a/litedram/gen-src/sdram_init/head.S
+++ b/litedram/gen-src/sdram_init/head.S
@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-#define STACK_TOP	0xff006000
+#include "microwatt_soc.h"
+#define STACK_TOP	(0x00006000 + DRAM_INIT_BASE)
 
 #define FIXUP_ENDIAN						   \
 	tdi   0,0,0x48;	  /* Reverse endian of b . + 8		*/ \
diff --git a/litedram/gen-src/sdram_init/main.c b/litedram/gen-src/sdram_init/main.c
index 9ba4fd1..36f3d06 100644
--- a/litedram/gen-src/sdram_init/main.c
+++ b/litedram/gen-src/sdram_init/main.c
@@ -5,12 +5,16 @@
 #include <stdarg.h>
 #include <stdio.h>
 
+#ifndef STANDALONE_MINI_BIOS
 #include <generated/git.h>
+#endif
 
 #include "console.h"
 #include "microwatt_soc.h"
 #include "io.h"
+#ifndef STANDALONE_MINI_BIOS
 #include "sdram.h"
+#endif
 #include "elf64.h"
 
 #define FLASH_LOADER_USE_MAP
@@ -284,13 +288,17 @@ uint64_t main(void)
 	}
 	printf("\n");
 	if (ftr & SYS_REG_INFO_HAS_DRAM) {
+#ifndef STANDALONE_MINI_BIOS
 		printf("LiteDRAM built from Migen %s and LiteX %s\n",
 		       MIGEN_GIT_SHA1, LITEX_GIT_SHA1);
 		sdrinit();
+#endif
 	}
 	if (ftr & SYS_REG_INFO_HAS_BRAM) {
-		printf("Booting from BRAM...\n");
-		return 0;
+        // allow a jump to a config-specified address (just like DRAM can)
+        val = readq(SYSCON_BASE + SYS_REG_BRAM_BOOTADDR);
+		printf("Booting from BRAM at %lx...\n", val);
+		return val;
 	}
 	if (try_flash) {
 		val = boot_flash(fl_off);