Using I2C with FullSpeed USB
Hi,
I was finally able to get my USB Device recognized and working, but I encountered a serious problem as I was adding functionality. It seems that the I2CREAD command takes too much time and the USB service is lost.
Does anyone have any ideas on how to get around this problem? The I2C device I am polling is a MCP23016 I/O expander.
Robert
My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.
Not as dumb as yesterday, but stupider than tomorrow!
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I have one idea, I'd like opinions on it please. Lack of experience prevents me from knowing if I am just heading for another set of problems.
How about adding a PIC 16F628 to poll the MCP23016 and use hardware USART to send a word whenever data from the I/O Expander changes?
I checked the datasheet and the 16F628 can go up to 5000 KBAUD at 20MHz while in Synchronous mode. Is that fast enough without the USB service dropping?
Robert
My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.
Not as dumb as yesterday, but stupider than tomorrow!
|
If you have a device with a hardware I2C port, you could use that instead of PBP's bit-banging ones. The hardware approach would take a lot less CPU cycles.
Charles Linquist
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Can you elaborate just a bit more please?
Robert
My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.
Not as dumb as yesterday, but stupider than tomorrow!
|
A lot of the newer PICs have a hardware I2C port. The 18F8722 for example, has two ports. Microchip calls these "SSP" or "MSSP" ports.
Just as SERIN and SEROUT use pure software to manipulate ports, I2CREAD and I2CWRITE use software to simulate a true hardware I2C port. Since everything is done in software, the processor is tied up 100% of the time during the entire operation.
HSERIN and HSEROUT use the PIC's USART. If these are used, the software simply needs to write to or read from a register, and hardware takes over to send or receive the bit stream. From a processor standpoint, HSEROUT is hundreds of times faster than SEROUT.
The same thing is true with I2C. If you can use the PIC's built-in hardware to do the task, it is MUCH quicker than using I2CREAD and I2CWRITE.
Unfortunately, I'm in the process right now of learning how to use the specialized I2C hardware. As a result, I'm not much of a resource (at least not today) when it comes to actual implementation.
Charles Linquist
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I'm using the 18F4550 as main processor and it has both the USB and SPP features. I have a LCD tied to the SPP port already, and nearly all the other pins are used.
Is there a device that could take I2C input and then output through USART? I know MicroChip has a lot of 'stuff', but I don't have any experience in this area.
Robert
My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.
Not as dumb as yesterday, but stupider than tomorrow!
|
how many byte do you read at the time?
still working with a single byte at the time? if so, just do loop and insert a USBSERVICE inside
As now i didn't use I2CREAD/WRITE with USB ones so...The MSSP is also suggest by me.
Charles.. i'm with you
Steve
It's not a bug, it's a random feature.
There's no problem, only learning opportunities.
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