DPPI channels can be enabled, disabled and grouped through the DPPI controller (DPPIC). The DPPIC is a split-security peripheral, and handles both secure and non-secure accesses.
A non-secure peripheral access will only be able to configure and control DPPI channels defined as non-secure in SPU's DPPI[n].PERM register(s). A secure peripheral access can control all DPPI channels, independently of the configuration in the DPPI[n].PERM register(s).
The DPPIC allows the creation of group of channels to be able to enable or disable all channels within a group simultaneously. The security attribute of a group of channels (secure or non-secure) is defined as follows:
- If all channels (enabled or not) in the group are non-secure, then the group is considered non-secure
- If at least one of the channels (enabled or not) in the group is secure, then the group is considered secure
A non-secure access to a DPPIC register, or a bitfield controlling a channel marked as secure in DPPI[n].PERM register(s), will be ignored:
- Write accesses will have no effect
- Read will always return a zero value
No exceptions are thrown when a non-secure access targets a register or bitfield controlling a secure channel. For example, if the bit i is set in the DPPI[n].PERM register (declaring the DPPI channel i as secure), then:
- Non-secure write accesses to registers CHEN, CHENSET and CHENCLR will not be able to write to bit i of those registers
- Non-secure write accesses to registers TASK_CHG[j].EN and TASK_CHG[j].DIS will be ignored if the channel group j contains at least one channel defined as secure (it can be the channel i itself or any channel declared as secured)
- Non-secure read accesses to registers CHEN, CHENSET and CHENCLR will always read zero for the bit at position i
For the channel configuration registers (DPPIC.CHG[n]), access from non-secure code is only possible if the included channels are all non-secure, whether the channels are enabled or not. If a DPPIC.CHG[g] register included one or more secure channels, then the group g is considered as secure and only a secure transfer can read or write DPPIC.CHG[g]. A non-secure write will be ignored and a non-secure read will return zero.
The DPPIC can subscribe to secure or non-secure channels through SUBSCRIBE_CHG[n] registers in order to trigger task for enabling or disabling groups of channels. But an event from a non-secure channel will be ignored if the group subscribing to this channel is secure. An event from a secure channel can trigger both secure and non-secure tasks.