bios: allow testing main_ram at init when using an external controller

litex/soc/software/bios/main.c

@@ -540,8 +540,12 @@ int main(int i, char **c)
 #endif
 #ifdef CSR_SDRAM_BASE
 	sdr_ok = sdrinit();
+#else
+#ifdef MAIN_RAM_TEST
+	sdr_ok = memtest();
 #else
 	sdr_ok = 1;
+#endif
 #endif
 	if(sdr_ok)
 		boot_sequence();

litex/soc/software/bios/sdram.c

@@ -1,10 +1,11 @@
 #include <generated/csr.h>
-#ifdef CSR_SDRAM_BASE
 
 #include <stdio.h>
 #include <stdlib.h>
 
+#ifdef CSR_SDRAM_BASE
 #include <generated/sdram_phy.h>
+#endif
 #include <generated/mem.h>
 #include <hw/flags.h>
 #include <system.h>
@@ -31,6 +32,8 @@ static void cdelay(int i)
 	}
 }
 
+#ifdef CSR_SDRAM_BASE
+
 void sdrsw(void)
 {
 	sdram_dfii_control_write(DFII_CONTROL_CKE|DFII_CONTROL_ODT|DFII_CONTROL_RESET_N);
@@ -509,6 +512,8 @@ static void read_level(int module)
 }
 #endif /* CSR_DDRPHY_BASE */
 
+#endif /* CSR_SDRAM_BASE */
+
 static unsigned int seed_to_data_32(unsigned int seed, int random)
 {
 	if (random)
@@ -676,6 +681,8 @@ int memtest(void)
 	}
 }
 
+#ifdef CSR_SDRAM_BASE
+
 #ifdef CSR_DDRPHY_BASE
 int sdrlevel(void)
 {