cpu/riscv_common: add puf_sram feature

cpu/riscv_common/Kconfig

@@ -12,6 +12,7 @@ config CPU_ARCH_RISCV
     select HAS_NEWLIB
     select HAS_PERIPH_CORETIMER
     select HAS_PICOLIBC if '$(RIOT_CI_BUILD)' != '1'
+    select HAS_PUF_SRAM
     select HAS_RUST_TARGET
     select HAS_SSP
 

cpu/riscv_common/Makefile.features

@@ -8,6 +8,7 @@ FEATURES_PROVIDED += cpp
 FEATURES_PROVIDED += libstdcpp
 FEATURES_PROVIDED += newlib
 FEATURES_PROVIDED += periph_coretimer
+FEATURES_PROVIDED += puf_sram
 FEATURES_PROVIDED += rust_target
 FEATURES_PROVIDED += ssp
 

cpu/riscv_common/include/cpu_conf_common.h

@@ -37,6 +37,11 @@
 #endif
 /** @} */
 
+/**
+ * @brief   Attribute for memory sections required by SRAM PUF
+ */
+#define PUF_SRAM_ATTRIBUTES __attribute__((used, section(".noinit")))
+
 /**
  * @brief   Declare the heap_stats function as available
  */

cpu/riscv_common/riscv_init.c

@@ -21,6 +21,17 @@
 #include "cpu_conf_common.h"
 #include "periph_cpu_common.h"
 
+#ifdef MODULE_PUF_SRAM
+#include "puf_sram.h"
+
+extern unsigned _sheap;
+
+void riscv_puf_sram_init(void)
+{
+    puf_sram_init((uint8_t *)&_sheap, SEED_RAM_LEN);
+}
+#endif /* MODULE_PUF_SRAM */
+
 void riscv_fpu_init(void)
 {
     /* Enable FPU if present */

cpu/riscv_common/start.S

@@ -27,6 +27,10 @@ _start_real:
 .option pop
     la sp, _sp
 
+#ifdef MODULE_PUF_SRAM
+    /* PUF */
+    call riscv_puf_sram_init
+#endif
 
     /* Load data section */
     la a0, _data_lma