When engaging in embedded development, do you often find yourself perplexed by the “dozens of manufacturers and hundreds of ARM chips”? Should you choose ARM7 or ARM9? Do you need an MMU? Is the built-in storage sufficient? There’s no need to panic; the core principle of selecting ARM chips is:precisely matching your requirements with the chip’s “core + peripherals”.This guide will clarify the selection principles, multi-core structures, suppliers, and application cases in simple terms, making it understandable even for beginners.
1. Focus on 7 Core Factors: These Elements Determine Chip Suitability
When selecting an ARM chip, do not start by looking at the model; first, confirm these 7 key points to filter out 80% of unsuitable options:
1. Check the ARM Core: Can it run the system you need?
The core is the “brain” of the chip, and the most critical aspect is whether it has an MMU (Memory Management Unit):
- To run systems like Linux or WinCE: choose a core with an MMU, such as ARM720T or ARM920T (corresponding chips include Samsung S3C2440, TI OMAP138);
- For lightweight RTOS like RT-Thread or FreeRTOS: an MMU is not necessary; ARM7TDMI (e.g., Atmel AT91M40800) is sufficient and more cost-effective;
- Speed requirements: ARM7 is suitable for tens of MHz (industrial control), ARM9 can reach 200-400MHz (multimedia devices), and ARM11 can go even higher (high-end handheld devices).
2. System Clock: Don’t Just Look at the “Maximum Frequency”
The clock determines the chip’s processing speed, but pay attention to two points:
- Some chips only have one main clock: for example, certain early chips cannot simultaneously meet the accuracy requirements for USB and audio clocks, so avoid them for multimedia devices;
- Advanced chips have multiple clock domains: for instance, the NXP LPC2478 can provide different frequencies for the CPU, USB, and LCD, balancing speed and peripheral needs.
3. Built-in Storage: Save Costs Where Possible
If the project does not require large-capacity storage, prioritize chips with built-in FLASH/SRAM to avoid external storage chips:
- For example, Atmel AT91FR40162: has 256K SRAM + 2M FLASH, suitable for simple control;
- Samsung S3C44B0: has 8K SRAM, sufficient for small projects;
- Note the capacity units: documents often use “Kbyte”; 1M FLASH = 1024Kbyte, so don’t miscalculate.
4. Peripherals: Missing One Could Change the Model
Peripherals are the “must-have filter”; match them to your project scenario:
- For audio (headphones, speakers): must include an IIS audio interface (e.g., Cirrus Logic EP7312);
- For display (PDA, small screen devices): must include an LCD controller (e.g., S3C2410 with TFT LCD controller);
- For analog signals (temperature collection, touch screens): must include ADC/DAC (e.g., Atmel AT91M55800 has 8 channels of ADC + 2 channels of DAC);
- To connect to a computer/USB drive: must include a USB interface (USB 1.1 is sufficient for daily use, USB 2.0 is suitable for high-speed transmission).
5. GPIO Count: Don’t Be Deceived by the “Maximum Count”
Many chips list the “GPIO count” as the “maximum value after pin multiplexing”; in practice, you need to calculate the “unused pins”:
- For example, a chip may state “64 GPIOs”, but if 20 of them are multiplexed with address and data lines, the actual usable count may only be 44; for projects with many peripherals, calculate this in advance.
6. Interrupt Controller: Affects Multitasking Efficiency
The ARM core itself only has “fast interrupts” and “standard interrupts”; manufacturers will add custom interrupt controllers:
- A good interrupt design: for example, Philips LPC2148 allows all GPIOs to be set for rising/falling edge interrupts, enabling tasks like infrared remote control and keyboard to run in the background without occupying the CPU;
- A poor interrupt design: for example, some early chips only have 5 external interrupts and can only be set for high/low levels, requiring polling for infrared reception, wasting CPU resources.
7. Packaging: Don’t Overlook Soldering and Wiring
Packaging determines the difficulty of PCB design and soldering costs:
- Surface mount packages (QFP, LQFP): suitable for manual soldering or standard surface mounting, allowing wiring on double-sided boards, ideal for small projects;
- BGA packaging: small chip area, but requires specialized soldering equipment and multi-layer PCB wiring, suitable for mass production projects; avoid for small batches.
2. Multi-core ARM Chips: These Combinations Are Suitable for Complex Scenarios
If your project requires “multimedia, hardware upgrades, multitasking”, a single ARM core may not be sufficient; consider these multi-core combinations:
|
Core Combination |
Core Advantages |
Suitable Scenarios |
Representative Chips |
|
ARM + DSP |
Enhanced audio/video processing capabilities |
MP3 players, digital cameras (image processing) |
TI OMAP5912 (ARM9 + DSP) |
|
ARM + FPGA |
Hardware can be upgraded online, high flexibility |
Industrial control (requires later adjustments to hardware logic) |
Altera EPXA1 (ARM9 + FPGA) |
|
Multi ARM Cores |
Parallel processing for multitasking |
High-end routers, automotive systems |
Some dedicated communication chips |
3. Overview of Mainstream Suppliers: Look for Chips from These Manufacturers
There’s no need to remember all manufacturers; focus on these categories that cover 90% of application scenarios:
- Western Manufacturers: TI (OMAP series, suitable for multimedia), Samsung (S3C series, cost-effective), Altera (ARM + FPGA, hardware flexibility), Philips (LPC series, industrial-grade stability);
- Japanese and Korean Manufacturers: Hyundai (HMS series, rich peripherals), Toshiba (early ARM chips, now focused on specialized fields);
- Domestic / Taiwanese Manufacturers: TSMC, UMC (mainly foundries), Huawei, ZTE (buy ARM cores to make communication-specific chips);
- Tip: For consumer electronics, prioritize Samsung and TI; for industrial equipment, look at Philips and Atmel.
4. Application Cases: Which Chips to Choose for These Scenarios?
The document provides “best solution recommendations” organized into common scenarios for your direct reference:
- High-end PDA / Handheld Devices: Choose one with LCD + USB + MMU, such as Intel PXA255 (ARM920T core, supports Linux);
- Portable MP3: Choose ARM + DSP, such as Cirrus Logic EP7312 (with IIS audio interface, built-in decoder);
- Digital Cameras: Choose one with image processing DSP, such as Agilent ADSP-BF533 (ARM + image DSP, fast photo processing);
- Set-top Boxes: Choose one with Ethernet + USB, such as STi5518 (ARM9 core, supports network and external hard drives);
- Industrial Sensors: Choose a low-cost ARM7, such as Atmel AT91M40800 (with built-in storage, sufficient for simple control).
5. Three Practical Tips for Selection
- First, list your “requirements”: Write down the “systems to run, necessary peripherals (like LCD/USB), and storage needs”; filtering chips against this list is faster than blindly looking at models;
- Check the latest information from manufacturers: ARM chips update quickly; today’s “best solution” may be outdated next year, so check the latest datasheets on the manufacturer’s website before selecting;
- Test packaging in small batches first: If using BGA packaging for the first time, buy a few samples to test soldering and confirm PCB wiring before placing a bulk order.
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