This page is about different ARM processors
The aim is to use an ARM7 chip.
We are biased towards the atmel AT91SAM7A3 (instead of the old plan, LPC2129).
- 100 pin is enough for nice functionality without the LBUS
- nice functionality. Atmel was always strong with the peripherals, and with the ARM core it's an unbeatable combination
- nice ADC (16 channels, 10 bit) and DMA for everything (called PDC)
- nice networking with CAN, UARTS and USB
- the only drawback is no-EEPROM, so we need to bridge this with some software (storing config and tables in flash)
The ancient page still has some info:
on-chip peripherals - was used as checklist when looking for uC candidates
The following points are important from my point of view:
the usage is obvious in most cases, check GenBoard/VerThree
- FLASH, mandatory ? 128 kbyte for basic functions. We use MMC for noncritical (black-box, logging) stuff
- SRAM, how much 16 kbyte+
- ADC, >= 10bit 4 onchip. We use MCP3208 for bigger boards or 144pin version with 8 ADC channels.
- external interrupt: not needed, that's only useful with input capture. ARM ITC seems to be very rich
- DAC: 2 channels would help, but not available. Any ideas for external chip? (we used PWM and RC filter on v3.x)
- core frequency is likely not an issue as it's always enough
- watchdog (always present)
- external 8bit ports not needed, 4 bit LBUS is fine (for 259 chips)
- external SPI port
- digital I/O not critical, the LBUS is fine, see above
- serial port (1+)
- USB generally not available: we use USB-RS232 or USB-CAN
- CAN 2+ MUST
- timer-related functions, see below
datasheet from page 214.... (and pinout)
- It seems we want to use the timer0 and timer1 for input capture and eventqueue with high period
- CAP1.x does not conflict that bad as CAP0.x (ADC input channels).
- we want 3 of MAT1.x for precise timed chip-enable signals for 259 chips. That allows to have dead-sharp timing (with some firmware tricks).
- the 4th match register T1MAT4 will be used to generate EventQueue? interrupt
- we only need 3 PWMs badly: 1 for injector PWMing and 2 for WBO2 pump (1 for each WBO2 channel). It comes nice to have extra PWMs, eg. for general purpose analog output.
YESS. This chip is awesome!
We have 8 input captures available: CAM / crank, crank-backup + 4 wheels + freqoutput MAP possible with 8 input captures!
PWM-ing uses it's own timer (at adress 0x14000) NOT Timer0/Timer1. The manual is confusing, but if you look at the registers and addresses (eg. page 230 of 306), it will be clear.
We'll use 40 .. 80 usec PWMing period .
Little guy needed or not?
Aren't we using an AVR (IO chip) to take care of Injector PWMing and flyback control? I feel that the IO chip is the best way to avoid pin mapping conflicts with the ARM boards. -Jörgen
No, it seems functionality per board was shrinked so much we don't need an AVR helper script. Pinmapping will be relatively easy, the only thing I asked is we
- leave AINx free for ADC inputs.
- control 259 latch enable with output-match capable outputs.
Even with arbitrary pinmapping it's _much_ less software than with a helper AVR chip, so we don't use that if not absolutely necessary.
- xQFP, 64 .. 144 pins ?
- pin pitch (anything 0.5, 0.635, 0.65, 0.80 mm OK)
- prototyping, how to solder: not a major criteria, we use professional production for prototypes too, since we need 20+
- forget xQFP - PGA changer
availability, product maturity
I'm against new products like Motorola MAC71xx, the first version is always buggy
- development tools: GCC port is available for ARM7
- compilers, debuggers, assemblers, simulators: does anyone uses simulators ?, not often. In the future, we'll make prototype on PC (C or java)
- flashers, real-time debug
- it seems all ARM cores have a JTAG (TAP) access to main real-time debugging features
- relatively cheap ($150) boxes are available to access TAP, do we need them or is it simple to make them ?
The MCU choice:
- LPC2292: 256k, 16k, 2xCAN, 8x10bit ADC [LQFP144]
- LPC2294: 256k, 16k, 4xCAN, 8x10bit ADC, LQFP144
- OKI [ML67Q2301] ? LQFP144, 4.5-5.5V, 384K, 16K, 4xCAN is DEAD, it never made to market
- Atmel: only BGA are with flash, rejected
- Motorola MAC71xx: not mature, rejected ?
- TI ?
- Cirrus Logic ? no ADC, BGA only, rejected
- ST: very similar to Philips LPC. 64pin package, 4 timers, 4x10bit ADC, USB or CAN, one 3v power. Inputs not 5v tolerant. BUT: eval kits developped 2 floors below my office :-)
- XC166 (someone put it on the bad page? oh, it's not ARM) could be acceptable but not enough reasons listed to switch from LPC2119
- design our own: (just kidding :-)