The N_As value describes the time a CAN frame needs on the wire when transmitted by the CAN controller. Even very short CAN FD frames need arround 100 usecs (bitrate 1Mbit/s, data bitrate 8Mbit/s). Having N_As to be zero (the former default) leads to 'no CAN frame separation' when STmin is set to zero by the receiving node. This 'burst mode' should not be enabled by default as it could potentially dump a high number of CAN frames into the netdev queue from the soft hrtimer context. This does not affect the system stability but is just not nice and cooperative. With this N_As/frame_txtime value the 'burst mode' is disabled by default. As user space applications usually do not set the frame_txtime element of struct can_isotp_options the new in-kernel default is very likely overwritten with zero when the sockopt() CAN_ISOTP_OPTS is invoked. To make sure that a N_As value of zero is only set intentional the value '0' is now interpreted as 'do not change the current value'. When a frame_txtime of zero is required for testing purposes this CAN_ISOTP_FRAME_TXTIME_ZERO u32 value has to be set in frame_txtime.
Showing the changes to include/uapi (1 of 2 files). Show all
Unified · Split
| @@ -137,20 +137,16 @@ struct can_isotp_ll_options { · 136 unmodified lines | |||
| 137 | #define CAN_ISOTP_WAIT_TX_DONE 0x400 /* wait for tx completion */ | 137 | #define CAN_ISOTP_WAIT_TX_DONE 0x400 /* wait for tx completion */ |
| 138 | #define CAN_ISOTP_SF_BROADCAST 0x800 /* 1-to-N functional addressing */ | 138 | #define CAN_ISOTP_SF_BROADCAST 0x800 /* 1-to-N functional addressing */ |
| 139 | 139 | ||
| 140 | /* default values */ | 140 | /* protocol machine default values */ |
| 141 | 141 | ||
| 142 | #define CAN_ISOTP_DEFAULT_FLAGS 0 | 142 | #define CAN_ISOTP_DEFAULT_FLAGS 0 |
| 143 | #define CAN_ISOTP_DEFAULT_EXT_ADDRESS 0x00 | 143 | #define CAN_ISOTP_DEFAULT_EXT_ADDRESS 0x00 |
| 144 | #define CAN_ISOTP_DEFAULT_PAD_CONTENT 0xCC /* prevent bit-stuffing */ | 144 | #define CAN_ISOTP_DEFAULT_PAD_CONTENT 0xCC /* prevent bit-stuffing */ |
| 145 | #define CAN_ISOTP_DEFAULT_FRAME_TXTIME 0 | 145 | #define CAN_ISOTP_DEFAULT_FRAME_TXTIME 50000 /* 50 micro seconds */ |
| 146 | #define CAN_ISOTP_DEFAULT_RECV_BS 0 | 146 | #define CAN_ISOTP_DEFAULT_RECV_BS 0 |
| 147 | #define CAN_ISOTP_DEFAULT_RECV_STMIN 0x00 | 147 | #define CAN_ISOTP_DEFAULT_RECV_STMIN 0x00 |
| 148 | #define CAN_ISOTP_DEFAULT_RECV_WFTMAX 0 | 148 | #define CAN_ISOTP_DEFAULT_RECV_WFTMAX 0 |
| 149 | 149 | ||
| 150 | #define CAN_ISOTP_DEFAULT_LL_MTU CAN_MTU | ||
| 151 | #define CAN_ISOTP_DEFAULT_LL_TX_DL CAN_MAX_DLEN | ||
| 152 | #define CAN_ISOTP_DEFAULT_LL_TX_FLAGS 0 | ||
| 153 | |||
| 154 | /* | 150 | /* |
| 155 | * Remark on CAN_ISOTP_DEFAULT_RECV_* values: | 151 | * Remark on CAN_ISOTP_DEFAULT_RECV_* values: |
| 156 | * | 152 | * |
| @@ -162,4 +158,24 @@ struct can_isotp_ll_options { · 5 unmodified lines | |||
| 162 | * consistency and copied directly into the flow control (FC) frame. | 158 | * consistency and copied directly into the flow control (FC) frame. |
| 163 | */ | 159 | */ |
| 164 | 160 | ||
| 161 | /* link layer default values => make use of Classical CAN frames */ | ||
| 162 | |||
| 163 | #define CAN_ISOTP_DEFAULT_LL_MTU CAN_MTU | ||
| 164 | #define CAN_ISOTP_DEFAULT_LL_TX_DL CAN_MAX_DLEN | ||
| 165 | #define CAN_ISOTP_DEFAULT_LL_TX_FLAGS 0 | ||
| 166 | |||
| 167 | /* | ||
| 168 | * The CAN_ISOTP_DEFAULT_FRAME_TXTIME has become a non-zero value as | ||
| 169 | * it only makes sense for isotp implementation tests to run without | ||
| 170 | * a N_As value. As user space applications usually do not set the | ||
| 171 | * frame_txtime element of struct can_isotp_options the new in-kernel | ||
| 172 | * default is very likely overwritten with zero when the sockopt() | ||
| 173 | * CAN_ISOTP_OPTS is invoked. | ||
| 174 | * To make sure that a N_As value of zero is only set intentional the | ||
| 175 | * value '0' is now interpreted as 'do not change the current value'. | ||
| 176 | * When a frame_txtime of zero is required for testing purposes this | ||
| 177 | * CAN_ISOTP_FRAME_TXTIME_ZERO u32 value has to be set in frame_txtime. | ||
| 178 | */ | ||
| 179 | #define CAN_ISOTP_FRAME_TXTIME_ZERO 0xFFFFFFFF | ||
| 180 | |||
| 165 | #endif /* !_UAPI_CAN_ISOTP_H */ | 181 | #endif /* !_UAPI_CAN_ISOTP_H */ |