Bit Twiddling Confusion

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Previous: 'Understanding PLIC_Init & PLIC_set_threshold'

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0:07Mention the poll¹

2:42Recap and set the stage for the day

3:56Embark on understanding PLIC_enable_interrupt()²

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3:56Embark on understanding PLIC_enable_interrupt()²

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3:56Embark on understanding PLIC_enable_interrupt()²

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7:32Consult demo_gpio.c for a use case of PLIC_enable_interrupt()

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7:32Consult demo_gpio.c for a use case of PLIC_enable_interrupt()

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7:32Consult demo_gpio.c for a use case of PLIC_enable_interrupt()

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12:18Consult env/hifive1.h for the INT_DEVICE_BUTTON_* and BUTTON_*_OFFSET defines

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12:18Consult env/hifive1.h for the INT_DEVICE_BUTTON_* and BUTTON_*_OFFSET defines

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12:18Consult env/hifive1.h for the INT_DEVICE_BUTTON_* and BUTTON_*_OFFSET defines

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16:15Consult PLIC_enable_interrupt() in conjunction with the FE310-G000 Interrupts and the SiFive PLIC Register Map table³

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16:15Consult PLIC_enable_interrupt() in conjunction with the FE310-G000 Interrupts and the SiFive PLIC Register Map table³

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16:15Consult PLIC_enable_interrupt() in conjunction with the FE310-G000 Interrupts and the SiFive PLIC Register Map table³

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19:06Calculating the value of INT_DEVICE_BUTTON_0 and the result of shifting it >> 3

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19:06Calculating the value of INT_DEVICE_BUTTON_0 and the result of shifting it >> 3

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19:06Calculating the value of INT_DEVICE_BUTTON_0 and the result of shifting it >> 3

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21:50Hunt for more information about the GPIO pins

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21:50Hunt for more information about the GPIO pins

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21:50Hunt for more information about the GPIO pins

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24:58Summarise what current_ptr is being set to and move on to working out how the current mask works

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24:58Summarise what current_ptr is being set to and move on to working out how the current mask works

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24:58Summarise what current_ptr is being set to and move on to working out how the current mask works

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27:47The current mask

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27:47The current mask

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27:47The current mask

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31:380x17 >> 3

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31:380x17 >> 3

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31:380x17 >> 3

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33:06miblo It's 128, according to: printf("%d\n", 1 << (0x17 & 0x7));

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33:06miblo It's 128, according to: printf("%d\n", 1 << (0x17 & 0x7));

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33:06miblo It's 128, according to: printf("%d\n", 1 << (0x17 & 0x7));

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37:41The AND operator

38:45Realise that it should be in hex

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38:45Realise that it should be in hex

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38:45Realise that it should be in hex

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39:08miblo It's not 7 and 17, though, it's 0x7 and 0x17

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39:08miblo It's not 7 and 17, though, it's 0x7 and 0x17

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39:08miblo It's not 7 and 17, though, it's 0x7 and 0x17

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39:52The current mask, take #2

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39:52The current mask, take #2

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39:52The current mask, take #2

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43:05miblo I think you should be shifting up the 1 by 0b00111 bits, if that makes a difference

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43:05miblo I think you should be shifting up the 1 by 0b00111 bits, if that makes a difference

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43:05miblo I think you should be shifting up the 1 by 0b00111 bits, if that makes a difference

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43:17The current mask, take #3

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43:17The current mask, take #3

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43:17The current mask, take #3

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44:43The address of current_ptr

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44:43The address of current_ptr

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44:43The address of current_ptr

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47:27miblo We're doing 0x17 >> 3? This does equal 2, apparently

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47:27miblo We're doing 0x17 >> 3? This does equal 2, apparently

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47:27miblo We're doing 0x17 >> 3? This does equal 2, apparently

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48:20Our conceptual understanding of PLIC_enable_interrupt()

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48:20Our conceptual understanding of PLIC_enable_interrupt()

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48:20Our conceptual understanding of PLIC_enable_interrupt()

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52:23miblo 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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52:23miblo 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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52:23miblo 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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53:24Target Enable 0 at 0x0C002082 in memory, and the relative location of current_ptr

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53:24Target Enable 0 at 0x0C002082 in memory, and the relative location of current_ptr

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53:24Target Enable 0 at 0x0C002082 in memory, and the relative location of current_ptr

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58:49Consult the FE310-G000 Interrupts and consider which bit PLIC_enable_interrupt() is setting

59:34azolotko 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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59:34azolotko 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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59:34azolotko 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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1:00:16What PLIC_enable_interrupt() does for source 0x8, to compare with the previous 0x17

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1:00:16What PLIC_enable_interrupt() does for source 0x8, to compare with the previous 0x17

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1:00:16What PLIC_enable_interrupt() does for source 0x8, to compare with the previous 0x17

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1:07:19Consider that it's computing the correct thing for gpio0, and look back at the 0x17 example

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1:07:19Consider that it's computing the correct thing for gpio0, and look back at the 0x17 example

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1:07:19Consider that it's computing the correct thing for gpio0, and look back at the 0x17 example

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1:12:38miblo What is current set to?

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1:12:38miblo What is current set to?

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1:12:38miblo What is current set to?

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1:14:30We are out of time for today

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Next: 'Understanding the Rest of the PLIC Driver & RTC_FREQUENCY'

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