riscv: add single register access, add csr access with an offset, exp…

…ose some CSRs register in the xml description

src/target/riscv32.c

@@ -65,6 +65,8 @@ typedef struct riscv32_regs {
 #define RV32_MATCH_BEFORE 0x00000000U
 #define RV32_MATCH_AFTER  0x00040000U
 
+static ssize_t riscv32_reg_read(target_s *target, uint32_t c, void *data, size_t max);
+static ssize_t riscv32_reg_write(target_s *target, uint32_t c, const void *data, size_t max);
 static void riscv32_regs_read(target_s *target, void *data);
 static void riscv32_regs_write(target_s *target, const void *data);
 static void riscv32_mem_read(target_s *target, void *dest, target_addr_t src, size_t len);
@@ -81,6 +83,8 @@ bool riscv32_probe(target_s *const target)
 	target->regs_size = sizeof(riscv32_regs_s);
 	target->regs_read = riscv32_regs_read;
 	target->regs_write = riscv32_regs_write;
+	target->reg_write = riscv32_reg_write;
+	target->reg_read = riscv32_reg_read;
 	target->mem_read = riscv32_mem_read;
 	target->mem_write = riscv32_mem_write;
 
@@ -120,6 +124,41 @@ static void riscv32_regs_write(target_s *const target, const void *const data)
 	riscv_csr_write(hart, RV_DPC, &regs->pc);
 }
 
+static inline ssize_t riscv32_bool_to_4(const bool ret)
+{
+	return ret ? 4 : -1;
+}
+
+static ssize_t riscv32_reg_read(target_s *target, const uint32_t reg, void *data, const size_t max)
+{
+	if (max != 4)
+		return -1;
+	/* Grab the hart structure  */
+	riscv_hart_s *const hart = riscv_hart_struct(target);
+	if (reg < 32)
+		return riscv32_bool_to_4(riscv_csr_read(hart, RV_GPR_BASE + reg, data));
+	if (reg == 32)
+		return riscv32_bool_to_4(riscv_csr_read(hart, RV_DPC, data));
+	if (reg >= RV_CSR_GDB_OFFSET)
+		return riscv32_bool_to_4(riscv_csr_read(hart, reg - RV_CSR_GDB_OFFSET, data));
+	return -1;
+}
+
+static ssize_t riscv32_reg_write(target_s *const target, const uint32_t reg, const void *data, const size_t max)
+{
+	if (max != 4)
+		return -1;
+	/* Grab the hart structure  */
+	riscv_hart_s *const hart = riscv_hart_struct(target);
+	if (reg < 32)
+		return riscv32_bool_to_4(riscv_csr_write(hart, RV_GPR_BASE + reg, data));
+	if (reg == 32)
+		return riscv32_bool_to_4(riscv_csr_write(hart, RV_DPC, data));
+	if (reg >= RV_CSR_GDB_OFFSET)
+		return riscv32_bool_to_4(riscv_csr_write(hart, reg - RV_CSR_GDB_OFFSET, data));
+	return -1;
+}
+
 /* Takes in data from abstract command arg0 and, based on the access width, unpacks it to dest */
 void riscv32_unpack_data(void *const dest, const uint32_t data, const uint8_t access_width)
 {

src/target/riscv_debug.c

@@ -137,6 +137,24 @@ static const char *const riscv_gpr_names[RV_GPRS_COUNT] = {
 	"s8", "s9", "s10", "s11",
 	"t3", "t4", "t5", "t6",
 };
+
+typedef struct riscv_csr_descriptor  {
+	const char *name;
+	const uint32_t csr_number; // fits in 16 bits actually (?)
+} riscv_csr_descriptor_s;
+
+static const riscv_csr_descriptor_s riscv_csrs[]={
+	{"mstatus",RV_CSR_STATUS},
+	{"misa",RV_CSR_MISA},
+	{"mie",	RV_CSR_MIE},
+	{"mtvec",	RV_CSR_MTVEC},
+	{"tscratch",RV_CSR_MSCRATCH},
+	{"mepc",	RV_CSR_MEPC},
+	{"mcause",RV_CSR_MCAUSE},
+	{"mtval",	RV_CSR_MTVAL},
+	{"mip",	RV_CSR_MIP},
+};
+
 // clang-format on
 
 /* General-purpose register types */
@@ -945,6 +963,17 @@ static size_t riscv_build_target_description(
 
 	/* XXX: TODO - implement generation of the FPU feature and registers */
 
+	/* Add main CSR registers*/
+	if (max_length != 0)
+		print_size = max_length - (size_t)offset;
+	offset += snprintf(buffer + offset, print_size, "</feature><feature name=\"org.gnu.gdb.riscv.csr\">");
+	for (size_t i = 0; i < ARRAY_LENGTH(riscv_csrs); i++) {
+		if (max_length != 0)
+			print_size = max_length - (size_t)offset;
+		offset += snprintf(buffer + offset, print_size, " <reg name=\"%s\" bitsize=\"%u\" regnum=\"%" PRIu32 "\" %s/>",
+			riscv_csrs[i].name, address_width, riscv_csrs[i].csr_number + RV_CSR_GDB_OFFSET,
+			gdb_reg_save_restore_strings[GDB_SAVE_RESTORE_NO]);
+	}
 	/* Add the closing tags required */
 	if (max_length != 0)
 		print_size = max_length - (size_t)offset;

src/target/riscv_debug.h

@@ -178,6 +178,20 @@ typedef struct riscv_hart {
 #define RV_TRIGGER_MODE_MASK          0xffff0000U
 #define RV_TRIGGER_SUPPORT_BREAKWATCH 0x00000004U
 
+// The CSR id when reported by GDB is shifted by RV_CSR_GDB_OFFSET
+// so they cannot collide with GPR registers, so you have to substract
+// RV_CSR_GDB_OFFSET from the value received from gdb
+#define RV_CSR_GDB_OFFSET 128
+#define RV_CSR_STATUS     0x300
+#define RV_CSR_MISA       0x301
+#define RV_CSR_MIE        0x304
+#define RV_CSR_MTVEC      0x305
+#define RV_CSR_MSCRATCH   0x340
+#define RV_CSR_MEPC       0x341
+#define RV_CSR_MCAUSE     0x342
+#define RV_CSR_MTVAL      0x343
+#define RV_CSR_MIP        0x344
+
 #define RV_TOPT_INHIBIT_NRST 0x00000001U
 
 void riscv_jtag_dtm_handler(uint8_t dev_index);