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theteaman
Joined: 04 Aug 2006
Posts: 98
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| Serial algorithm with interrupts |
 Posted: Sat Aug 26, 2006 7:02 pm |
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Hello
I need to be able to read a large amount of data from a PC, over UART, to the PIC. Now I have the UART all set up and it works. But my problem relates to the algorithm itself. Basically, the amount of data that will be transferred will be greater than the total RAM the PIC has, and I was hoping to transfer the data into a Flash memory IC as the data is received to overcome this problem.
If I have an interrupt handler that simply sets a global variable to the value returned by getc(), this wont work because the handler will be called faster than the main code has time to deal with it, and this will result in lost data.
If I have an interrupt handler that stores to a buffer, then in my case, wont I still lose data eventually (it will just take longer for the buffer to overflow)?
Does anyone have any ideas of what I can do? The only thing I can think of is to send the data from the PC in fixed sized chunks (and wait for each chunk to complete before sending the next one), but surely there is another way? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sat Aug 26, 2006 10:21 pm |
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| Use a FRAM device for storage. The write time is pretty much instant. Receive the data into a ring buffer. Anytime data is in the ring buffer, store to the FRAM device. Implement flow control, RTS, CTS. |
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theteaman
Joined: 04 Aug 2006
Posts: 98
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| Posted: Sat Aug 26, 2006 11:27 pm |
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| Mark wrote: | | Use a FRAM device for storage. The write time is pretty much instant. Receive the data into a ring buffer. Anytime data is in the ring buffer, store to the FRAM device. Implement flow control, RTS, CTS. |
Well I'm using a flash memory at the moment (M25P) is that the same thing as FRAM? it has page program cycle tim of between 1.4 and 5ms, is this fast enough for me to do what you are saying? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sun Aug 27, 2006 8:05 am |
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| theteaman wrote: | | Mark wrote: | | Use a FRAM device for storage. The write time is pretty much instant. Receive the data into a ring buffer. Anytime data is in the ring buffer, store to the FRAM device. Implement flow control, RTS, CTS. |
Well I'm using a flash memory at the moment (M25P) is that the same thing as FRAM? it has page program cycle tim of between 1.4 and 5ms, is this fast enough for me to do what you are saying? |
Nope, it is not the same. A FRAM has a program cycle time of 0ms. You don't give any specifics about the communication so no one can possibly answer your question. If it takes less than 5ms to receive a "block" of data then the answer is no. |
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Guest
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| Posted: Sun Aug 27, 2006 8:12 pm |
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[quote="Mark"] | theteaman wrote: |
Nope, it is not the same. A FRAM has a program cycle time of 0ms. You don't give any specifics about the communication so no one can possibly answer your question. If it takes less than 5ms to receive a "block" of data then the answer is no. |
Well, you havent given me any specifics about what I should be specific about......
anyway, the solution is to send the data in chunks. I cannot find FRAM at digikey, and I cant imagine it being a serial interface, but rather parallel which I do not have enough pins for nor the space to add circuitry to share them, so the answer is simply to be more 'cooperative' on the PC sender end. |
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specialk
Joined: 12 Nov 2005
Posts: 27
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| Posted: Sun Aug 27, 2006 8:15 pm |
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| Mark wrote: | | Nope, it is not the same. A FRAM has a program cycle time of 0ms. |
There is no such thing as a program cycle time of 0ms. Looking at a popular manufacturer (Ramtron), their parallel FRAM modules have an access time as low as 60ns and as high as 120ns (http://www.ramtron.com/doc/Products/Nonvolatile/Nonvolatile_list.asp?ID=6). Their serial modules are even slower (because of the serial overhead). While fast (by relatively slow PIC standards), it is not instantaneous.
-special [k] |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Sun Aug 27, 2006 8:19 pm |
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| specialk wrote: | | Mark wrote: | | Nope, it is not the same. A FRAM has a program cycle time of 0ms. |
There is no such thing as a program cycle time of 0ms. |
I think, Mark wanted to say that writing cycle of FRAM is under 1ms. Most types of nonvolatile memory have write times one the order of few ms. C'mon, 120ns is almost zer0 compared to 1ms. |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sun Aug 27, 2006 9:16 pm |
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| specialk wrote: | | Mark wrote: | | Nope, it is not the same. A FRAM has a program cycle time of 0ms. |
There is no such thing as a program cycle time of 0ms. Looking at a popular manufacturer (Ramtron), their parallel FRAM modules have an access time as low as 60ns and as high as 120ns (http://www.ramtron.com/doc/Products/Nonvolatile/Nonvolatile_list.asp?ID=6). Their serial modules are even slower (because of the serial overhead). While fast (by relatively slow PIC standards), it is not instantaneous.
-special [k] |
Obviously there is no 0ms write time but to the application there would be. The part writes at the bus speed so you can in essence write the data as fast as the bus speed without any need to delay. In essence, 0ms. While we are at in Cornflake, no one said anything about access times. The orginal poster referred to page program cycle time of 1.4ms-5ms. The device will be unable to be accessed during this time. The FRAM has no such waiting period. It is 0ms which is what I was referring to.
Cheerios |
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treitmey
Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA
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| Posted: Mon Aug 28, 2006 8:07 am |
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mouser has the ramtron devices.. Here is the search for FM24C256
[url]http://www.mouser.com/search/Refine.aspx?Ne=1447464+254016&Ntt=*FM24C256*&Msb=0&Mkw=FM24C256&N=1323038[/url]
Last edited by treitmey on Tue Dec 26, 2006 4:56 pm; edited 1 time in total |
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specialk
Joined: 12 Nov 2005
Posts: 27
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| Posted: Mon Aug 28, 2006 2:19 pm |
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| Quote: | Obviously there is no 0ms write time but to the application there would be. The part writes at the bus speed so you can in essence write the data as fast as the bus speed without any need to delay. In essence, 0ms. While we are at in Cornflake, no one said anything about access times. The orginal poster referred to page program cycle time of 1.4ms-5ms. The device will be unable to be accessed during this time. The FRAM has no such waiting period. It is 0ms which is what I was referring to.
Cheerios |
I'm sorry if my reply seemed rude or hurtful, I did not intend to offend you (or anyone else). However, while you may think that 120ns isn't a long time (as I said before, by relatively slow PIC standards), data access speeds (which in the case of Ramtron FRAM refer to reading OR writing) have been a serious issue for a number of colleagues who had to abandon the Microchip PICs in favor of much more robust (and faster) ARM microprocessors with DMA.
Theteaman may want to consider an FRAM device or possibly an SRAM. I'm not discouraging its use. I have had a lot of success with Maxim's NV SRAM; however, they are parallel modules (~70ns access time), so given his requirements, I agree with you that Ramtron's serial FRAM modules would be more appropriate. FRAM modules are, as you said, more than adaquite for Microchip PIC applications.
Again, I apologize for my curt reply and for offending you.
-special [k] |
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