Application and selection of 32-bit RISC CPU ARM chips

Since its official establishment in 1990, ARM has continuously made breakthroughs in the development of 32-bit RISC (Reduced Instruction Set Computer) CPUs, and its structure has evolved from V3 to V6. Since its establishment, ARM has been selling intellectual property to major semiconductor manufacturers as an IP (Intelligence Property) provider, and has never been involved in the production and sales of chips. In addition, the cores it designs have significant advantages such as low power consumption and low cost. Therefore, it has received strong support from many semiconductor manufacturers and complete machine manufacturers, and has achieved great success in the field of 32-bit embedded applications. It currently occupies more than 75% of the 32-bit RISC embedded product market. It has established a market leadership position in the field of low-power, low-cost embedded applications. There are now more than 50 international companies designing and producing ARM chips. Companies such as ZTE and Huawei have purchased ARM cores for the design of communication-specific chips.

Currently, the most popular ARM cores include ARM7TDMI, StrongARM, ARM720T, ARM9TDMI, ARM922T, ARM940T, RM946T, ARM966T, ARM10TDMI, etc. Since V5, ARM has provided Piccolo DSP cores to chip designers for designing ARMDSP SOC (System On Chip) structure chips. In addition, ARM chips have also received support from many real-time operating system (RTOS) suppliers, including Windows CE, Linux, pSOS, VxWorks, Nucleus, EPOC, uCOS, BeOS, etc.

With the development of domestic embedded application field, ARM chips will inevitably gain wide attention and application. However, since ARM chips have more than a dozen core structures, more than 70 chip manufacturers, and ever-changing internal function configuration combinations, it brings certain difficulties to developers when choosing solutions. Therefore, it is very necessary to do a comparative study of ARM chips.

1 General principles for ARM chip selection

From the application perspective, this article gives a detailed explanation of the main factors that should be considered when selecting an ARM chip.

1.1 ARM Core

If you want to use WinCE or Linux operating systems to reduce software development time, you need to choose ARM chips with MMU (memory management unit) functions above ARM720T. ARM720T, Stron-gARM, ARM920T, ARM922T, and ARM946T all have MMU functions. ARM7TDMI does not have MMU and does not support Windows CE and most Linuxes, but there are a few Linuxes such as uCLinux that do not require MMU support.

1.2 System Clock Controller

The system clock determines the processing speed of the ARM chip. The processing speed of ARM7 is 0.9MIPS/MHz, and the common ARM7 chip system master clock is 20MHz-133MHz. The processing speed of ARM9 is 1.1MIPS/MHz, and the common ARM9 system master clock is 100MHz-233MHz. The highest ARM10 can reach 700MHz. Different chips handle clocks differently. Some chips have only one master clock frequency, and such chips may not be able to take into account the accuracy of UART and audio clocks at the same time, such as Cirrus Logic's EP7312; some chips have internal clock controllers that can provide the same frequency clocks for the CPU core and USB, UART, DSP, audio and other functional components, such as PHILIPS's SAA7750 and other chips.

1.3 Internal memory capacity

When large-capacity memory is not needed, you can consider using an ARM chip with built-in memory. See Table 1.

Table 1 ARM chips with built-in memory

Chip Model Supplier FLASH Capacity ROM Capacity SRAM Capacity

1.4 USB interface

Many ARM chips have built-in USB controllers, and some chips even have both USB Host and USB Slave controllers. See Table 2.

1.5 GPIO Number

In the manuals provided by some chip vendors, the maximum possible number of GPIOs is often stated, but many pins are multiplexed with address lines, data lines, serial port lines, etc. Therefore, it is necessary to calculate the actual number of GPIOs that can be used during system design.

1.6 Interrupt Controller

The ARM core only provides two interrupt vectors: fast interrupt (FIQ) and standard interrupt (IRQ). However, each semiconductor manufacturer adds its own interrupt controller when designing the chip to support hardware interrupts such as serial port, external interrupt, clock interrupt, etc. External interrupt control is an important factor that must be considered when selecting a chip. Reasonable external interrupt design can greatly reduce the workload of task scheduling. For example, PHILIPS's SAA7750, all GPIOs can be set to FIQ or IRQ, and four interrupt modes can be selected: rising edge, falling edge, high level, and low level. This allows tasks such as infrared remote control reception, thumbwheels, and keyboards to run as background programs. The EP7312 chip of Cirrus Logic has only 4 external interrupt sources, and each interrupt source can only be a low level or high level interrupt. When used to receive infrared signals, it must use the query method, which will waste a lot of CPU time. [page]

1.7 IIS (Integrate Interface of Sound) interface

That is, integrated audio interface. If the designer applies high-frequency products, IIS bus interface is necessary.

1.8 nWAIT signal

External bus speed control signal. Not every ARM chip provides this signal pin. By using this signal and a cheap GAL chip, you can implement the interface with WLAN cards and Bluetooth cards that comply with the PCMCIA standard without the need for an additional high-cost PCMCIA dedicated control chip. In addition, this signal is also necessary when an external DSP coprocessor needs to be expanded.

1.9 RTC (Real Time Clock)

Many ARM chips provide real-time clock functions, but in different ways. For example, the RTC of Cirrus Logic's EP7312 is just a 32-bit counter, which needs to be calculated by software to get the year, month, day, hour, minute, and second; while the RTC of chips such as SAA7750 and S3C2410 directly provides the year, month, day, hour, minute, and second format.

1.10 LCD Controller

Some ARM chips have built-in LCD controllers, and some even have built-in 64K color TFT LCD controllers. When designing PDAs and handheld display and recording devices, it is more appropriate to choose ARM chips with built-in LCD controllers, such as S1C2410.

1.11 PWM Output

Some ARM chips have 2 to 8 PWM outputs, which can be used for motor control or voice output, etc.

1.12 ADC and DAC

Some ARM chips have built-in 2-8 channel 8-12 bit general ADCs, which can be used for battery detection, touch screen and temperature monitoring, etc. PHILIPS's SAA7750 has a built-in 16-bit stereo audio ADC and DAC, and comes with headphone driver.

1.13 Expansion Bus

Most ARM chips have external SDRAM and SRAM expansion interfaces. Different ARM chips can expand the number of chips, that is, the number of chip select lines, and the external data bus is 8-bit, 16-bit or 32-bit. Some special application ARM chips, such as the German Micronas PUC3030A, do not have external expansion functions.

1.14 UART and IrDA

Almost all ARM chips have 1-2 UART interfaces, which can be used to communicate with PC or debug with Angel. The general ARM chip communication baud rate is 115, 200bps, and the UART communication baud rate of a few ARM chips designed for Bluetooth technology applications can reach 920Kbps, such as Linkup's L7205.

1.15 DSP coprocessor, see Table 3.

1.16 Built-in FPGA

Some ARM chips have built-in FPGAs, which are suitable for fields such as communications. See Table 4.

1.17 Clock Counter and Watchdog

Generally, ARM chips have 2 to 4 16-bit or 32-bit clock counters and a watchdog counter.

1.18 Power Management Function

The power consumption of ARM chips is proportional to the operating frequency. Generally, ARM chips have low power consumption mode, sleep mode and shutdown mode.

1.19 DMA Controller

Some ARM chips have integrated DMA (Direct Memory Access), which can exchange data with external devices such as hard disks at high speed, while reducing the use of CPU resources during data exchange.

In addition, the internal functional components that can be selected are: HDLC, SDLC, CD-ROM Decoder, Ethernet MAC, VGA controller, DC-DC. The built-in interfaces that can be selected are: IIC, SPDIF, CAN, SPI, PCI, PCMCIA.

Finally, we need to explain the packaging issue. The main packages of ARM chips now include QFP, TQFP, PQFP, LQFP, BGA, LBGA, etc. BGA packaging has the characteristics of small chip area, which can reduce the area of ​​PCB board, but it requires special welding equipment and cannot be welded manually. In addition, ARM chips with BGA packaging cannot complete PCB wiring with double-sided boards, and require multi-layer PCB board wiring. [page]

2 Selection of multi-core ARM chips

In order to enhance multi-tasking, mathematical computing, multimedia and network processing capabilities, some suppliers provide ARM chips with multiple cores built in. Currently common structures include ARM+DSP, ARM+FPGA, ARM+ARM, etc.

2.1 Multiple ARM Cores

In order to enhance multi-tasking and multimedia processing capabilities, some ARM chips have multiple ARM cores built in. For example, the PP5002 of Portal Player integrates two ARM7TDMI cores, which can be used in encoders or decoders of portable MP3 players. MinSpeed, a company that was separated from Conexant and specializes in the design and production of high-speed communication chips, integrates 2 to 4 ARM7TDMI cores in many of its high-speed communication chips.

2.2 ARM Core + DSP Core

In order to enhance mathematical operation and multimedia processing functions, many suppliers have added DSP coprocessors to their ARM chips. Commonly added DSP coprocessors include ARM's Piccolo DSP core, OAK's 16-bit fixed-point DSP core, TI's TMS320C5000 series DSP core, Motorola's 56K DSP core, etc. See Table 3.

2.3 ARM Core + FPGA

In order to improve the online upgrade capability of system hardware, some companies have integrated FPGA into ARM chips. See Table 4.

3 Major ARM chip suppliers

Currently, the famous European and American semiconductor companies that can provide ARM chips include: Intel, Texas Instruments, Samsung Semiconductor, Motorola, Philips Semiconductor, STMicroelectronics, Eheng Semiconductor, Conexant, Analog Devices, Agilent, Qualcomm, Atmel, Intersil, Alcatel, Altera, Cirrus Logic, Linkup, Parthus, LSI Logic, Micronas, Silicon Wave, Virata, Portalplayer inc., NetSilicon, Parthus. See Table 5. Many famous Japanese semiconductor companies or Toshiba, Mitsubishi Semiconductor, Epson, Fujitsu Semiconductor, Matsushita Semiconductor and other companies have invested heavily in the development of independent 32-bit CPU structures in the early days, but now they have turned to purchasing ARM's cores for new product design. Because they purchased ARM copyrights late, there are no ARM chips available for sale now, while OKI, NEC, AKM, OAK, Sharp, Sanyo, Sony, Rohm and other Japanese semiconductor companies have already indicated the production of ARM chips. South Korea's Hyundai Semiconductor also produces and provides ARM chips. In addition, many foreign equipment manufacturers also use ARM cores to design their own dedicated chips, such as IBM and 3COM in the United States and Singapore's Innovation Technology. Companies in Taiwan that can provide ARM chips include TSMC, UMC, Huabang Electronics, etc. Other mainland companies that have purchased ARM cores and are designing their own proprietary dedicated chips include ZTE Communications.

4 Examples of selection options

The best solutions listed in Table 6 are for reference only. Due to the rapid development of SOC integrated circuits, the best solution today may not be the best solution tomorrow. Therefore, when choosing a solution at any time, you should search widely among the major ARM chip suppliers to find the most suitable chip.