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| im-tomu | [umarcor] I have a couple of questions about designing/customising a board based on UP5K. Hope someone can help: | 09:32 |
|---|---|---|
| im-tomu | - Fomu, and several other boards do include an external 12, 24 or 48 MHz crystal. However, the documentation says that UP5K devices do already have two internal oscillators (10KHz and 48MHz). Is an external (crystal) oscillator a requirement? Or was it included in Fomu due to stability (because the main programming interface is USB)? | 09:32 |
| im-tomu | - The SPI flash memory on the https://www.crowdsupply.com/1bitsquared/icebreaker-fpga is described as "*128 Mbit (16 MB) quad SPI double data rate (QSPI-DDR) flash*". There is a comparison table where it's said that Fomu has "*16 Mbit SPI*". However, the BoM of the Fomu (https://github.com/im-tomu/fomu-hardware/tree/master/archive/pvt#bill-of-materials) and the Hardware Specifications of the icebreaker (https://github.com/icebreaker | 09:32 |
| im-tomu | - Can someone confirm which SPI does the Fomu include? Is it *QSPI-DDR* (as the Icebreaker) or is it *QSPI* only? | 09:32 |
| tpb | Title: iCEBreaker FPGA | Crowd Supply (at www.crowdsupply.com) | 09:32 |
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| daveshah | umarcor: neither the accuracy nor stability (it is heavily influenced by noise on Vcore) of the internal oscillator would be good enough for reliable USB | 09:40 |
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| im-tomu | [umarcor] david: thanks. what about other not so demanding uses? The design I'm thinking about would be programmed through SPI only (no USB or uC on board). Then, it would be used for motor control, with VGA/SPI-LCD/RGB-LCD, other external SPI/I2C peripherals. I know that accuracy/stability is not very important for motor control or SPI. But I'm not sure about other cases. Would you recommend to put a crystal in any case? | 09:45 |
| daveshah | I think people have had trouble with VGA and the internal oscillator due to the jitter | 09:52 |
| im-tomu | [umarcor] david: if that happened, I would assume that using UARTs for communicating with external uCs would also be "broken" without an external crystal. Hence, I will squash the components to make place for it. Thanks for your help. | 09:54 |
| daveshah | I've had UARTs working OK on the internal oscillator but it's not ideal | 09:57 |
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| tnt | daveshah: I've never really had that many issue with the internal osc, I always found that a bit weird. I mean, I've run whole USB stack on it with no issues whatsoever ... | 11:10 |
| im-tomu | [umarcor] sylvain: did you use linear regulators or dc-dc? | 11:26 |
| tnt | that board uses linear regs. | 11:42 |
| tnt | But given the power usage on vcore on an ice40 ... a dc-dc switching converter makes little sense. | 11:42 |
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| im-tomu | [tcal-x] FYI the most recent release of circuitpython (6.0.0) appears to have broken Fomu support. I've filed an issue including a bit of work narrowing down the commit window where things stopped working: https://github.com/adafruit/circuitpython/issues/3841 | 20:57 |
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