41 lines
2.9 KiB
Plaintext
41 lines
2.9 KiB
Plaintext
[video member=miotatsu stream_platform=twitch project=riscy title="Bit Twiddling Confusion" vod_platform=youtube id=xS_s23rxHqg annotator=Miblo]
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[0:07][Mention the poll[ref
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site=Twitter
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page="Poll: Should I hire an artist to make better thumbnails for my content?"
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url=https://twitter.com/hmn_riscy/status/833911733752385536]]
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[2:42][Recap and set the stage for the day]
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[3:56][Embark on understanding PLIC_enable_interrupt()[ref
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site="SiFive Developers"
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page="Freedom E310-G000 Manual"
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url=https://www.sifive.com/documentation/chips/freedom-e310-g000-manual/]][:research]
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[7:32][Consult demo_gpio.c for a use case of PLIC_enable_interrupt()][:research]
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[12:18][Consult env/hifive1.h for the INT_DEVICE_BUTTON_* and BUTTON_*_OFFSET defines][:research]
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[16:15][Consult PLIC_enable_interrupt() in conjunction with the FE310-G000 Interrupts and the SiFive PLIC Register Map table[ref
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site="SiFive Developers"
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page="E3 Coreplex Manual"
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url=https://static.dev.sifive.com/pdfjs/web/viewer.html?file=https://static.dev.sifive.com/SiFive-E3-Coreplex-v1.2.pdf]][:research]
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[19:06][Calculating the value of INT_DEVICE_BUTTON_0 and the result of shifting it >> 3][:blackboard :research]
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[21:50][Hunt for more information about the GPIO pins][:research]
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[24:58][Summarise what current_ptr is being set to and move on to working out how the current mask works][:research]
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[27:47][The current mask][:blackboard :research]
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[31:38][0x17 >> 3][:blackboard :research]
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[33:06][@miblo][It's 128, according to: printf("%d\\n", 1 << (0x17 & 0x7));]
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[37:41][The AND operator][:math]
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[38:45][Realise that it should be in hex][:research]
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[39:08][@miblo][It's not 7 and 17, though, it's 0x7 and 0x17]
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[39:52][The current mask, take #2][:blackboard :research]
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[43:05][@miblo][I think you should be shifting up the 1 by 0b00111 bits, if that makes a difference]
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[43:17][The current mask, take #3][:blackboard :research]
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[44:43][The address of current_ptr][:blackboard :research]
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[47:27][@miblo][We're doing 0x17 >> 3? This does equal 2, apparently]
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[48:20][Our conceptual understanding of PLIC_enable_interrupt()][:research]
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[52:23][@miblo][I think it's moving the current_ptr to one of the target 1 enables, i.e. the third one, or 0x0C002082 (with 0x0C002080 being the first target 1 enable)]
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[53:24][Target Enable 0 at 0x0C002082 in :memory, and the relative location of current_ptr][:blackboard :research]
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[58:49][Consult the FE310-G000 Interrupts and consider which bit PLIC_enable_interrupt() is setting]
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[59:34][@azolotko][source & 0x7 can produce values from 0 to 7 depending on value of source. So the shift may vary, it doesn't have to be exactly 7]
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[1:00:16][What PLIC_enable_interrupt() does for source 0x8, to compare with the previous 0x17][:blackboard :research]
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[1:07:19][Consider that it's computing the correct thing for gpio0, and look back at the 0x17 example][:blackboard :research]
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[1:12:38][@miblo][What is current set to?]
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[1:14:30][We are out of time for today]
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[/video]
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