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target/riscv: restrict BSCAN-related commands to before-init
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Logically, BSCAN tunneling is used to establish a connection, therefore
it should be set up before the communication starts (i.e. before
`init`).

Moreover, current implementation does not support changing
`bscan_tunnel_ir_width` after `init`. This is evident by RISC-V handler
of the `init` itself.
Link: https://github.com/riscv-collab/riscv-openocd/blob/9a23c9e67978f77d9166102cefc7b537b714b561/src/target/riscv/riscv.c#L467-L481

Change-Id: I817c6a996f7f7171b2286e181daf1092bd358f69
Signed-off-by: Evgeniy Naydanov <[email protected]>
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@en-sc
en-sc committed Aug 14, 2024
1 parent 9a23c9e commit 342f294
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Showing 3 changed files with 36 additions and 32 deletions.
11 changes: 8 additions & 3 deletions doc/openocd.texi
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Original file line number Diff line number Diff line change
Expand Up @@ -11354,10 +11354,15 @@ Display/set the current core displayed in GDB. This is needed only if
@code{riscv smp} was used.
@end deffn

@deffn {Command} {riscv use_bscan_tunnel} value
@deffn {Command} {riscv use_bscan_tunnel} width [type]
Enable or disable use of a BSCAN tunnel to reach the Debug Module. Supply the
width of the DM transport TAP's instruction register to enable. Supply a
value of 0 to disable.
@var{width} of the DM transport TAP's instruction register to enable. The
@var{width} should fit into 7 bits. Supply a value of 0 to disable.
Pass a second argument (optional) to indicate Bscan Tunnel Type:
@enumerate
@item 0:(default) NESTED_TAP
@item 1: DATA_REGISTER
@end enumerate

This BSCAN tunnel interface is specific to SiFive IP. Anybody may implement
it, but currently there is no good documentation on it. In a nutshell, this
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55 changes: 27 additions & 28 deletions src/target/riscv/riscv.c
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Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,8 @@ struct scan_field select_idcode = {
};

static bscan_tunnel_type_t bscan_tunnel_type;
int bscan_tunnel_ir_width; /* if zero, then tunneling is not present/active */
#define BSCAN_TUNNEL_IR_WIDTH_NBITS 7
uint8_t bscan_tunnel_ir_width; /* if zero, then tunneling is not present/active */
static int bscan_tunnel_ir_id; /* IR ID of the JTAG TAP to access the tunnel. Valid when not 0 */

static const uint8_t bscan_zero[4] = {0};
Expand All @@ -67,7 +68,6 @@ static struct scan_field select_user4 = {
};


static uint8_t bscan_tunneled_ir_width[4] = {5}; /* overridden by assignment in riscv_init_target */
static struct scan_field _bscan_tunnel_data_register_select_dmi[] = {
{
.num_bits = 3,
Expand All @@ -80,8 +80,8 @@ static struct scan_field _bscan_tunnel_data_register_select_dmi[] = {
.in_value = NULL,
},
{
.num_bits = 7,
.out_value = bscan_tunneled_ir_width,
.num_bits = BSCAN_TUNNEL_IR_WIDTH_NBITS,
.out_value = &bscan_tunnel_ir_width,
.in_value = NULL,
},
{
Expand All @@ -98,8 +98,8 @@ static struct scan_field _bscan_tunnel_nested_tap_select_dmi[] = {
.in_value = NULL,
},
{
.num_bits = 7,
.out_value = bscan_tunneled_ir_width,
.num_bits = BSCAN_TUNNEL_IR_WIDTH_NBITS,
.out_value = &bscan_tunnel_ir_width,
.in_value = NULL,
},
{
Expand Down Expand Up @@ -300,7 +300,6 @@ void select_dmi_via_bscan(struct target *target)
int dtmcontrol_scan_via_bscan(struct target *target, uint32_t out, uint32_t *in_ptr)
{
/* On BSCAN TAP: Select IR=USER4, issue tunneled IR scan via BSCAN TAP's DR */
uint8_t tunneled_ir_width[4] = {bscan_tunnel_ir_width};
uint8_t tunneled_dr_width[4] = {32};
uint8_t out_value[5] = {0};
uint8_t in_value[5] = {0};
Expand All @@ -316,8 +315,8 @@ int dtmcontrol_scan_via_bscan(struct target *target, uint32_t out, uint32_t *in_
tunneled_ir[1].num_bits = bscan_tunnel_ir_width;
tunneled_ir[1].out_value = ir_dtmcontrol;
tunneled_ir[1].in_value = NULL;
tunneled_ir[2].num_bits = 7;
tunneled_ir[2].out_value = tunneled_ir_width;
tunneled_ir[2].num_bits = BSCAN_TUNNEL_IR_WIDTH_NBITS;
tunneled_ir[2].out_value = &bscan_tunnel_ir_width;
tunneled_ir[2].in_value = NULL;
tunneled_ir[3].num_bits = 1;
tunneled_ir[3].out_value = bscan_zero;
Expand All @@ -329,7 +328,7 @@ int dtmcontrol_scan_via_bscan(struct target *target, uint32_t out, uint32_t *in_
tunneled_dr[1].num_bits = 32 + 1;
tunneled_dr[1].out_value = out_value;
tunneled_dr[1].in_value = in_value;
tunneled_dr[2].num_bits = 7;
tunneled_dr[2].num_bits = BSCAN_TUNNEL_IR_WIDTH_NBITS;
tunneled_dr[2].out_value = tunneled_dr_width;
tunneled_dr[2].in_value = NULL;
tunneled_dr[3].num_bits = 1;
Expand All @@ -343,8 +342,8 @@ int dtmcontrol_scan_via_bscan(struct target *target, uint32_t out, uint32_t *in_
tunneled_ir[2].num_bits = bscan_tunnel_ir_width;
tunneled_ir[2].out_value = ir_dtmcontrol;
tunneled_ir[1].in_value = NULL;
tunneled_ir[1].num_bits = 7;
tunneled_ir[1].out_value = tunneled_ir_width;
tunneled_ir[1].num_bits = BSCAN_TUNNEL_IR_WIDTH_NBITS;
tunneled_ir[1].out_value = &bscan_tunnel_ir_width;
tunneled_ir[2].in_value = NULL;
tunneled_ir[0].num_bits = 1;
tunneled_ir[0].out_value = bscan_zero;
Expand Down Expand Up @@ -473,7 +472,6 @@ static int riscv_init_target(struct command_context *cmd_ctx,
}
h_u32_to_le(ir_user4, ir_user4_raw);
select_user4.num_bits = target->tap->ir_length;
bscan_tunneled_ir_width[0] = bscan_tunnel_ir_width;
if (bscan_tunnel_type == BSCAN_TUNNEL_DATA_REGISTER)
bscan_tunnel_data_register_select_dmi[1].num_bits = bscan_tunnel_ir_width;
else /* BSCAN_TUNNEL_NESTED_TAP */
Expand Down Expand Up @@ -4382,18 +4380,23 @@ COMMAND_HANDLER(riscv_resume_order)

COMMAND_HANDLER(riscv_use_bscan_tunnel)
{
int irwidth = 0;
uint8_t irwidth = 0;
int tunnel_type = BSCAN_TUNNEL_NESTED_TAP;

if (CMD_ARGC > 2) {
LOG_ERROR("Command takes at most two arguments");
if (CMD_ARGC < 1 || CMD_ARGC > 2)
return ERROR_COMMAND_SYNTAX_ERROR;
} else if (CMD_ARGC == 1) {
COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], irwidth);
} else if (CMD_ARGC == 2) {
COMMAND_PARSE_NUMBER(int, CMD_ARGV[0], irwidth);
COMMAND_PARSE_NUMBER(int, CMD_ARGV[1], tunnel_type);

if (CMD_ARGC >= 1) {
COMMAND_PARSE_NUMBER(u8, CMD_ARGV[0], irwidth);
assert(BSCAN_TUNNEL_IR_WIDTH_NBITS < 8);
if (irwidth >= (uint8_t)1 << BSCAN_TUNNEL_IR_WIDTH_NBITS) {
command_print(CMD, "'value' does not fit into %d bits.",
BSCAN_TUNNEL_IR_WIDTH_NBITS);
return ERROR_COMMAND_ARGUMENT_OVERFLOW;
}
}
if (CMD_ARGC == 2)
COMMAND_PARSE_NUMBER(int, CMD_ARGV[1], tunnel_type);
if (tunnel_type == BSCAN_TUNNEL_NESTED_TAP)
LOG_INFO("Nested Tap based Bscan Tunnel Selected");
else if (tunnel_type == BSCAN_TUNNEL_DATA_REGISTER)
Expand Down Expand Up @@ -5195,18 +5198,14 @@ static const struct command_registration riscv_exec_command_handlers[] = {
{
.name = "use_bscan_tunnel",
.handler = riscv_use_bscan_tunnel,
.mode = COMMAND_ANY,
.mode = COMMAND_CONFIG,
.usage = "value [type]",
.help = "Enable or disable use of a BSCAN tunnel to reach DM. Supply "
"the width of the DM transport TAP's instruction register to "
"enable. Supply a value of 0 to disable. Pass A second argument "
"(optional) to indicate Bscan Tunnel Type {0:(default) NESTED_TAP , "
"1: DATA_REGISTER}"
.help = "Enable or disable use of a BSCAN tunnel to reach DM."
},
{
.name = "set_bscan_tunnel_ir",
.handler = riscv_set_bscan_tunnel_ir,
.mode = COMMAND_ANY,
.mode = COMMAND_CONFIG,
.usage = "value",
.help = "Specify the JTAG TAP IR used to access the bscan tunnel. "
"By default it is 0x23 << (ir_length - 6), which map some "
Expand Down
2 changes: 1 addition & 1 deletion src/target/riscv/riscv.h
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Original file line number Diff line number Diff line change
Expand Up @@ -365,7 +365,7 @@ extern struct scan_field select_idcode;
extern struct scan_field *bscan_tunneled_select_dmi;
extern uint32_t bscan_tunneled_select_dmi_num_fields;
typedef enum { BSCAN_TUNNEL_NESTED_TAP, BSCAN_TUNNEL_DATA_REGISTER } bscan_tunnel_type_t;
extern int bscan_tunnel_ir_width;
extern uint8_t bscan_tunnel_ir_width;

int dtmcontrol_scan_via_bscan(struct target *target, uint32_t out, uint32_t *in_ptr);
void select_dmi_via_bscan(struct target *target);
Expand Down

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