New quirks handler (closes #38 #533)

Useful functions when you are confronted with equipment which does not respect the protocol, which behaves strangely or when you wish to move away from the standard. Thank you @mhei for the great initial version.

New quirks handler (closes #38 #533)
Useful functions when you are confronted with equipment which does not respect the protocol, which behaves strangely or when you wish to move away from the standard. Thank you @mhei for the great initial version.
Stéphane Raimbault
1 parent b0c05667
Showing 9 changed files with 142 additions and 6 deletions
docs/index.md
docs/modbus_disable_quirks.md
docs/modbus_enable_quirks.md
src/modbus-private.h
src/modbus-rtu.c
src/modbus-tcp.c
src/modbus.c
src/modbus.h
tests/unit-test-client.c
@@ -251,6 +251,11 @@ error codes into error message strings; for details refer to
 ## Miscellaneous
+To deviate from the Modbus standard, you can enable or disable quirks with:
+
+- [modbus_disable_quirks](modbus_disable_quirks.md)
+- [modbus_enable_quirks](modbus_enable_quirks.md)
+
 The `_LIBMODBUS_VERSION_STRING_` constant indicates the libmodbus version the
 program has been compiled against. The variables 'libmodbus_version_major',
 'libmodbus_version_minor', 'libmodbus_version_micro' give the version the
+# modbus_disable_quirks
+
+## Name
+
+modbus_disable_quirks - disable a list of quirks according to a mask
+
+## Synopsis
+
+```c
+int modbus_disable_quirks(modbus_t *ctx, unsigned int quirks_mask);
+```
+
+## Description
+
+The function shall disable the quirks according to the provided mask. It's
+useful to revert changes applied by a previous call to
+[modbus_enable_quirks](modbus_enable_quirks.md)
+
+To reset all quirks, you can use the specific value `MODBUS_QUIRK_ALL`.
+
+```c
+modbus_enable_quirks(ctx, MODBUS_QUIRK_MAX_SLAVE | MODBUS_QUIRK_REPLY_TO_BROADCAST);
+
+...
+
+// Reset all quirks
+modbus_disable_quirks(ctx, MODBUS_QUIRK_ALL);
+```
+
+## Return value
+
+The function shall return 0 if successful. Otherwise it shall return -1 and set
+errno.
+
+## See also
+
+- [modbus_enable_quirks](modbus_enable_quirks.md)
+# modbus_enable_quirks
+
+## Name
+
+modbus_enable_quirks - enable a list of quirks according to a mask
+
+## Synopsis
+
+```c
+int modbus_enable_quirks(modbus_t *ctx, unsigned int quirks_mask);
+```
+
+## Description
+
+The function is only useful when you are confronted with equipment which does
+not respect the protocol, which behaves strangely or when you wish to move away
+from the standard.
+
+In that case, you can enable a specific quirk to workaround the issue, libmodbus
+offers the following flags:
+
+- `MODBUS_QUIRK_MAX_SLAVE` allows slave adresses between 247 and 255.
+- `MODBUS_QUIRK_REPLY_TO_BROADCAST` force a reply to a broacast request when the
+  device is a slave in RTU mode (should be enabled on the slave device).
+
+You can combine the flags by using the OR logical operator.
+
+## Return value
+
+The function shall return 0 if successful. Otherwise it shall return -1 and set
+errno.
+
+## See also
+
+- [modbus_disable_quirks](modbus_disable_quirks.md)
@@ -96,6 +96,7 @@ struct _modbus {
     int s;
     int debug;
     int error_recovery;
+    int quirks;
     struct timeval response_timeout;
     struct timeval byte_timeout;
     struct timeval indication_timeout;
@@ -91,8 +91,10 @@ static const uint8_t table_crc_lo[] = {
  * internal slave ID in slave mode */
 static int _modbus_set_slave(modbus_t *ctx, int slave)
 {
+    int max_slave = (ctx->quirks & MODBUS_QUIRK_MAX_SLAVE) ? 255 : 247;
+
     /* Broadcast address is 0 (MODBUS_BROADCAST_ADDRESS) */
-    if (slave >= 0 && slave <= 247) {
+    if (slave >= 0 && slave <= max_slave) {
         ctx->slave = slave;
     } else {
         errno = EINVAL;
@@ -76,8 +76,10 @@ static int _modbus_tcp_init_win32(void)
 static int _modbus_set_slave(modbus_t *ctx, int slave)
 {
+    int max_slave = (ctx->quirks & MODBUS_QUIRK_MAX_SLAVE) ? 255 : 247;
+
     /* Broadcast address is 0 (MODBUS_BROADCAST_ADDRESS) */
-    if (slave >= 0 && slave <= 247) {
+    if (slave >= 0 && slave <= max_slave) {
         ctx->slave = slave;
     } else if (slave == MODBUS_TCP_SLAVE) {
         /* The special value MODBUS_TCP_SLAVE (0xFF) can be used in TCP mode to
@@ -176,6 +176,14 @@ typedef enum
     MODBUS_ERROR_RECOVERY_PROTOCOL      = (1<<2)
 } modbus_error_recovery_mode;
+typedef enum
+{
+    MODBUS_QUIRK_NONE                   = 0,
+    MODBUS_QUIRK_MAX_SLAVE              = (1<<1),
+    MODBUS_QUIRK_REPLY_TO_BROADCAST     = (1<<2),
+    MODBUS_QUIRK_ALL                    = 0xFF
+} modbus_quirks;
+
 MODBUS_API int modbus_set_slave(modbus_t* ctx, int slave);
 MODBUS_API int modbus_get_slave(modbus_t* ctx);
 MODBUS_API int modbus_set_error_recovery(modbus_t *ctx, modbus_error_recovery_mode error_recovery);
@@ -237,6 +245,8 @@ MODBUS_API int modbus_reply(modbus_t *ctx, const uint8_t *req,
                             int req_length, modbus_mapping_t *mb_mapping);
 MODBUS_API int modbus_reply_exception(modbus_t *ctx, const uint8_t *req,
                                       unsigned int exception_code);
+MODBUS_API int modbus_enable_quirks(modbus_t *ctx, unsigned int quirks_mask);
+MODBUS_API int modbus_disable_quirks(modbus_t *ctx, unsigned int quirks_mask);
 /**
  * UTILS FUNCTIONS
@@ -451,9 +451,26 @@ int main(int argc, char *argv[])
     printf("* modbus_write_registers: ");
     ASSERT_TRUE(rc == -1 && errno == EMBMDATA, "");
-    /** SLAVE REPLY **/
+    /** SLAVE ADDRESS **/
     old_slave = modbus_get_slave(ctx);
+    printf("\nTEST SLAVE ADDRESS:\n");
+
+    printf("1/2 Not compliant slave address is refused: ");
+    rc = modbus_set_slave(ctx, 248);
+    ASSERT_TRUE(rc == -1, "Slave address of 248 shouldn't be allowed");
+
+    printf("2/2 Not compliant slave address is allowed: ");
+    modbus_enable_quirks(ctx, MODBUS_QUIRK_MAX_SLAVE);
+    rc = modbus_set_slave(ctx, 248);
+    ASSERT_TRUE(rc == 0, "Not compliant slave address should have been accepted");
+
+    modbus_disable_quirks(ctx, MODBUS_QUIRK_MAX_SLAVE);
+    rc = modbus_set_slave(ctx, old_slave);
+    ASSERT_TRUE(rc == 0, "Uanble to restore slave value")
+
+    /** SLAVE REPLY **/
+
     printf("\nTEST SLAVE REPLY:\n");
     modbus_set_slave(ctx, INVALID_SERVER_ID);
     rc = modbus_read_registers(ctx, UT_REGISTERS_ADDRESS,