33.7.8.4 Continuous Read Mode

The QSPI is compatible with Continuous Read Mode (CRM) which is implemented in some Serial Flash memories.

The CRM allows to reduce the instruction overhead by excluding the instruction code from the instruction frame. When CRM is activated in a Serial Flash memory (by a specific option code), the instruction code is stored in the memory. For the next instruction frames, the instruction code is not required, as the memory uses the stored one.

In the QSPI, CRM is used when reading data from the memory (INSTFRAME.TFRTYPE=0x1). The addresses of the system bus read accesses are often non-sequential, this leads to many instruction frames with always the same instruction code. By disabling the sending of the instruction code, the CRM reduces the access time of the data.

To be functional, this mode must be enabled in both the QSPI and the Serial Flash memory. The CRM is enabled in the QSPI by setting the CRM bit in the INSTRFRAME register (INSTFRAME.CRMODE=1, INSTFRAME.TFRTYPE must be 0x1). The CRM is enabled in the Serial Flash memory by sending a specific option code.