VoCore: SPI & MicroSD 9

Now I am back to SPI driver for the microSD.
Thanks to Noltari, made such great process, this is the post http://vonger.cn/?topic=vocore-second-spi

SPI_CS1 is working normal now. We found the SD card not working is caused by the SPI speed is too high when SD card in init process.(Noltari SPI-GPIO firmware works, confirmed that is the problem).

RT5350 SPI lowest speed is 937.5KHz, but SD card init request speed is lower than 400KHz. It is a hardware broken.

But do not that hurry to say this SPI-microSD dead, let’s think this another way, at least, we have a temporary solution here 😀 Noltari’s firmware is able to make SPI flash and SPI microSD work same time already, just the boot time much longer, from 30seconds to 50 seconds..

We did not dead here yet. 😀 I think there still have some chance to make it happen.

What is SPI?
http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus

How SPI transfer data?
From my understanding, SPI is working this way: Data -> Message -> Bytes
Data buffer is split into small messages, one message is about 512bytes, the bytes in the message are send through SPI one by one.
Message is the atom SPI operation. That means, it won’t change to other SPI attributes(such as clock speed, chip select, bits length etc) until one message is done.

Before message send, the upper SPI driver will call spi_setup to setup the transfer attributes(in rt2880-spi.c). The chance is here.

My plan is to combine the two SPI drivers, hardware driver and software driver. For high speed SPI devices we can use hardware(write to hardware register), for low speed(< 935KHz) devices we can use software(SPI-bitbang, write to GPIOs). From datasheet, the GPIO mode and SPI mode can be easily switched by writing to the pinctrl register. Just need some tricks to make sure the two drivers won't fight each other. :)
There will be a new powerful SPI driver for all boards have such problem, I'd better to patch this in spi.c but not rt2880-spi.c.

About CPU consume, software SPI will cost a lot of CPU for high speed device, but for low speed ones, the performance is much better. SD card requested 400KHz for init only, so it just send hundred bytes, that cost can be ignored, so no effect to hole system.

2 thoughts on “VoCore: SPI & MicroSD 9

  1. Sucks I wasnt mentioned for saying about the 100khZ part first but thats fine ill mention it here :) glad to see progress tho.

Comments are closed.