Need info about latchless 8MB 4.5-port EBI

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I've gone through a lot in life so I forgot about what I had been talking about on this forum. This topic has been talked about over and over, but I need answers fast.

 

I've been reading the datasheet of ATXMEGA128A1U and XMEGA AU to see if it's really possible to use all 24 address bits/pins. It doesn't say so anywhere. Someone wrote on the forum that a 4.5-port mode actually works, but it hasn't been documented and I cannot find a correct connection in the datasheet that describes the pinout for such an EBI mode.

 

I'm expecting something like PORTH=Data, PORTJ=Addr8, PORTK=Addr16, PORTE=Addr24, PORTF.0=Read, PORTF.1=Write. I'm not sure how to activate it and how to test these pins because my Xplained board has a hardwired SRAM with latches and no pins for it available as a header to test with an oscilloscope. I want no latches because I saw the diagrams of EBI timing and that it would be extremely slow to use latches or an 8MB SDRAM. I want to know if there's an 8MB SRAM, but I couldn't find it anywhere. It's gotta exist somewhere. It needs to be 8MB instead of 16MB because I'm planning to use the 24-th pin/bit for accessing the display and it needs to be the most RAM-having 8-bit game console ever with the fastest display that renders with DMA that sends bytes scanline by scanline.

 

For my project that I've been talking about for a while now and because of which I became so boring to you all probably, I need to make a PCB with that XMEGA and SRAM as well as a proper connector for the display so I need to know the correct pinout for this 4.5-port EBI. Does anyone know that pinout? Does anyone know if there's an 8MB SRAM?

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Foxcat385 wrote:
Does anyone know if there's an 8MB SRAM?
Yes as a 4Mx16bit from Cypress Semiconductor.

Cypress

CY62187EV30 MoBL®: 64-Mbit (4M x 16) Static RAM

http://www.cypress.com/documentation/datasheets/cy62187ev30-mobl-64-mbit-4m-x-16-static-ram?source=search&cat=technical_documents

https://octopart.com/search?q=CY62187EV30

"Dare to be naïve." - Buckminster Fuller

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I've gone through a lot in life

Hope you are OK now.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I'm alright now.

 

Why is that chip more expensive than a 2GB DDR3 board?

 

I still don't know how to activate and connect the undocumented 4.5-port EBI correctly. Anyone have experience?

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Foxcat385 wrote:
Why is that chip more expensive than a 2GB DDR3 board?

  • IIRC one SRAM bit is 6 FETs vs. 1 FET for one DRAM bit.
  • Production quantity is much greater for DRAM.
  • Process capability (lots of bits, reduce the die area)

"Dare to be naïve." - Buckminster Fuller

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What would be the fastest and cheapest RAM for my XMEGA? The price of a single chip must NOT exceed $7 as the console would be expensive in mass-production because just 1000 units make it be 80% of the original price, amaik.

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With sdram, you latch the address the you can read a row of data sequentially without having to re-latch the address. If the row length of the sdram is equal or greater than the number of pixels on a line of your lcd, then you're home free. The processor either via programmed i/o or dma just does a read and the data gets clocked into your lcd. So you only need to latch a new address every line of the lcd. This may or may not be an advantage depending on how everything actually works. There's also psram that uses sdram internally but appears as static ram. There's only one supplier still making it and it is 1V8 only.
Renesas have a nice ARM chip with 10MB ram on chip and a lcd driver. Especially for lcd applications. I think there is an MBED supported board for it. I dare say it would be more than fast enough for your application.

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Foxcat385 wrote:
What would be the fastest and cheapest RAM for my XMEGA?
SDRAM.

The least expensive and most available are 16bit SDRAM; likely due to use by the millions in routers attached to MIPS or ARM MPU, and, some high pin count ARM Cortex-M MCU.

Next up are 8bit SDRAM.

4bit SDRAM - 3-port EBI, used on multiple XMEGA128A1U boards, source code exists (app note AVR1312), XMEGA AU has an orthogonal DMA controller (memory-to-memory, etc.).

Might look at Atmel's XMEGA128A1U board and its SRAM; uses 2 latches and 2-port EBI.

http://www.atmel.com/Images/Atmel-42211-XMEGA-A1U-Xplained-Pro_User-Guide.pdf (pages 15, 16)

"Dare to be naïve." - Buckminster Fuller

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I have the XMEGA128A1U board, but I think that the external SRAM will be slow with its latches according to the EBI timing diagram and that I cannot connect an external display to the EBI bus on the LCD connector if I don't have an extra chip select. This is why I'm thinking of making my own board with just what it needs to have.

 

I suppose I'll go for the SDRAM. I found MT48LC8M8A2 which is the alternative with an 8-bit data port unlike the one on a Xplain board for XMEGA. I found it at a reasonable price. It should be faster than the one with 4-bit mode. I'm not sure if an 8-bit SDRAM mode is possible, but I've heard of it. Is it possible to mix 8-bit SDRAM mode + parallel 8-bit LCD with one chip select?

 

Now, speaking of displays, I'm going to buy a parallel ST7775 display which has an 8-bit port and can have 16-bit colors.

Last Edited: Sat. Jan 30, 2016 - 12:38 PM
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Oh my... Seen the diagram again and decided to use SRAM instead. Please excuse me for my bad decisions and quickly changing them. I just don't know what to use when there's so many flaws in so many things and it takes lots of calculations to get it right.

 

I guess I'll be looking for the SRAM 4PORT NOALE variant. According to my calculations, 64MHz is 15ns and that will should be the SRAM's speed. It needs to be at least 512kB. Mouser doesn't give such results.

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You can't determine the ram speed from clock! Or vice-versa. You've got clock to control delays, setup and hold times and delays due to the physical interconnect. As well, you need to take into account temperature variation and production tolerance. Flaws? What 'flaws' do you speak of? Things that don't work like you expect?

I'd suggest you do some benchmarks as to the speed of your solutions and determine your direction by facts.

 

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I'm confused. I don't know what kind of RAM speed I would need for the SRAM 4PORT NOALE mode at 64MHz.

 

By flaws, I mean cost of RAM more than $7, data transfer delay longer than 6 CPU cycles and capacity less than 512kB.

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They're not flaws. A flaw is a defect.
To figure out the memory speed, you get the timing diagram for the xmega and for the ram chip. Add up the delays. The numbers will tell you.
Eg, for a read you might start counting when the xmega address is stable, then the ram data sheet will tell you how long to get stable data out. Add the xmega setup time. The xmega may also have a hold time where the data must remain stable after a certain point.