arch/riscv: add semihosting support for RISC-V
We add RISC-V semihosting based serial console for JTAG based early
debugging.
The RISC-V semihosting specification is available at:
https://github.com/riscv/riscv-semihosting-spec/blob/main/riscv-semihosting-spec.adoc
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Kautuk Consul <kconsul@ventanamicro.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/lib/semihosting.c b/arch/riscv/lib/semihosting.c
new file mode 100644
index 0000000..d6593b0
--- /dev/null
+++ b/arch/riscv/lib/semihosting.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2022 Ventana Micro Systems Inc.
+ */
+
+#include <common.h>
+
+long smh_trap(int sysnum, void *addr)
+{
+ register int ret asm ("a0") = sysnum;
+ register void *param0 asm ("a1") = addr;
+
+ asm volatile (".align 4\n"
+ ".option push\n"
+ ".option norvc\n"
+
+ "slli zero, zero, 0x1f\n"
+ "ebreak\n"
+ "srai zero, zero, 7\n"
+ ".option pop\n"
+ : "+r" (ret) : "r" (param0) : "memory");
+
+ return ret;
+}