Cortex-M4 Delivers 210 DMIPS Using 0-wait Memory
STM32 F4 Cortex-M4
ART Accelerator
STMicroelectronics' 168 MHz STM32 F4 series delivers 210 DMIPS using 0-wait state flash memory for the Cortex-M4 floating point processor (Fig. 1). This is possible because of the ART (adaptive real time) Accelerator (Fig. 2). ART is essentially a single level cache based on 256 128-bit entries. It also has an 8 entry data cache.
ART Accelerator only caches the first 128-bit word of a sequential code sequence because once this word is used the next sequential word can be fetched from the flash memory that does not run fast enough to provide 0-wait state operation. The Cortex-M4 runs 16-bit or 32-bit instructions so the 128-bit word holds at least four instructions. TheF4 series has up to 1 Mbyte of flash. The 192 Kbytes of RAM is split allowing simultaneous access to 16 Kbytes and a 112 Kbyte block. There is also 528 bytes of OTP (one time programmable) memory. The off-chip memory controller handles Compact Flash, SRAM, PSRAM, NAND and NOR flash.
The chip uses very little power. It uses 38.6 mA or 230 uA/MHz running at full speed. It only needs 1uA to run the real time clock (RTC). The chip requires 1.7V to 3.6V DC.
In addition to floating point, the Cortex-M4 core adds DSP instructions that take advantage of the single cycle MAC and barrel shifter. There is on-chip cryptography support for AES 128, 192, 256, Triple DES, plus MD5 and SHA-1 hash.
Communication includes support for a variety of SPI, I2C and UARTs plus I2S support. High speed interfaces include 10/100 Ethernet, USB with OTG support plus a pair of CAN 2.0b interfaces. The SDIO interface provides MMC support. DMA and GPIO are available as well. There is a 54 Mbyte/s 8- to 14-bit parallel camera interface.
On the analog side there is up to three 12-bit, 2.4 Msample/s ADC. These support up to 24 channels and 7.2 Msamples/s in triple interleaved mode. There are two 12-bit DACs converters
The chips are available in LQFP packages as well as a 10mm by 10mm BGA.The F4 is compatible with the L1, F1, and F2 series. The L1 series is an even lower power Cortex-M3 chip. STMicroelectronics has a number of evaluation kits available. The $349 STM3240G-EVAL board provides the most extensive support. The low cost $14.90 STM32F4DISCOVERY provides access to there I/O pins and includes an on-board USB-based debugger.
