Here is an app note from ARM describing the interrupt behavior of Cortex-M1 microcontrollers.
The ARM Cortex-M1 processor was developed for the usage with FPGAs (Field Programmable Gate Arrays) and it is targeting low-cost applications in which costs, ease of use and low interrupt latency are critical. Such low interrupt latency applications can include real-time control systems.
The processor implements the Thumb instruction set, with several additional Thumb-2 instructions to enable interrupt handling in Thumb state and upwards compatibility with ARM Cortex-M3. It includes 13 general purpose registers (R0 – R12), a Link Register (LR), a Stack Pointer (SP), a Program Counter (PC) and an xPSR (Program Status Register). The processor has 2 Tightly Coupled Memories (TCMs) interfaces, one for the instruction side (ITCM) and another for the data side (DTCM) of the processor, which could be connected to internal FPGA on-chip RAM blocks. Further the processor contains an AHB-Lite interface which allows the processor to fetch instructions or load/store data as a master in an AHB-Lite system.