27.5.2 Control B
The CTRLB register contains the mode and source settings for the CRC. It is not writable when the CRC is busy or when an NMI has been triggered.
| Name: | CTRLB |
| Offset: | 0x01 |
| Reset: | 0x00 |
| Property: | - |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| MODE[1:0] | SRC[1:0] | ||||||||
| Access | R/W | R/W | R/W | R/W | |||||
| Reset | 0 | 0 | 0 | 0 | |||||
Bits 5:4 – MODE[1:0] CRC Flash Access Mode
The CRC can be enabled during internal Reset initialization to verify Flash sections before letting the CPU start (see the device data sheet fuse description). If the CRC is enabled during internal Reset initialization, the MODE bit field will read out non-zero when normal code execution starts. To ensure proper operation of the CRC under code execution, write the MODE bit to 0x0 again.
| Value | Name | Description |
|---|---|---|
| 0x0 | PRIORITY | The CRC module runs a single check with priority to Flash. The CPU is halted until the CRC completes. |
| other | - | Reserved |
Bits 1:0 – SRC[1:0] CRC Source
The CRC can be enabled during internal Reset initialization to verify Flash sections before letting the CPU start (see fuse description). If the CRC is enabled during internal Reset initialization, the SRC bit field will read out as FLASH, BOOTAPP, or BOOT when normal code execution starts (depending on the configuration).
| Value | Name | Description |
|---|---|---|
| 0x0 | FLASH | The CRC is performed on the entire Flash (boot, application code, and application data sections). |
| 0x1 | BOOTAPP | The CRC is performed on the boot and application code sections of Flash. |
| 0x2 | BOOT | The CRC is performed on the boot section of Flash. |
| 0x3 | - | Reserved. |