Getting the PWM Interrupts to Fire | RISCY BUSINESS Episode Guide

0:07Plug SiFive's Linux-capable HiFive Unleashed chip¹

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0:07Plug SiFive's Linux-capable HiFive Unleashed chip¹

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0:07Plug SiFive's Linux-capable HiFive Unleashed chip¹

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5:28Check out the HiFive Unleashed specs² with exciting thoughts for it in RISCY BUSINESS

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5:28Check out the HiFive Unleashed specs² with exciting thoughts for it in RISCY BUSINESS

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5:28Check out the HiFive Unleashed specs² with exciting thoughts for it in RISCY BUSINESS

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16:04Plan to port pcalc to RISC-V to work on the HiFive Unleashed

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16:04Plan to port pcalc to RISC-V to work on the HiFive Unleashed

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16:04Plan to port pcalc to RISC-V to work on the HiFive Unleashed

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21:35Determine to continue our investigation into the trap on mstatus in pwm_speed_test.c and to run it in gdb

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21:35Determine to continue our investigation into the trap on mstatus in pwm_speed_test.c and to run it in gdb

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21:35Determine to continue our investigation into the trap on mstatus in pwm_speed_test.c and to run it in gdb

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25:12Read section 6.2.4 - Debugging Running Programs³

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25:12Read section 6.2.4 - Debugging Running Programs³

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25:12Read section 6.2.4 - Debugging Running Programs³

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27:33Comment out the set_csr(mie, MIP_MTIP) and set_csr(mstatus, MSTATUS_MIE) calls in main()

28:06Make and upload pwm_speed_test

29:49Reset the board, to see that we don't trap

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29:49Reset the board, to see that we don't trap

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29:49Reset the board, to see that we don't trap

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29:56Uncomment the set_csr(mstatus, MSTATUS_MIE) call in main()

30:08Make, upload and reset to find that we unexpectedly fail to trap

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30:08Make, upload and reset to find that we unexpectedly fail to trap

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30:08Make, upload and reset to find that we unexpectedly fail to trap

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31:15Reset the board in safe mode, and find that we still fail to trap

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31:15Reset the board in safe mode, and find that we still fail to trap

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31:15Reset the board in safe mode, and find that we still fail to trap

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32:41Uncomment the handle_m_time_interrupt() and set_csr(mie. MIP_MTIP) calls in main()

33:10Run to find that we trap after a short delay

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33:10Run to find that we trap after a short delay

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33:10Run to find that we trap after a short delay

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33:46Read carefully through handle_m_time_interrupt()

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33:46Read carefully through handle_m_time_interrupt()

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33:46Read carefully through handle_m_time_interrupt()

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36:29Copy the busy loop from led_fade.c into uart_init() in init.c, and reduce the wait time in handle_m_time_interrupt() to 2 seconds

38:11Run the program to find that we trap after waiting 2 seconds

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38:11Run the program to find that we trap after waiting 2 seconds

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38:11Run the program to find that we trap after waiting 2 seconds

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38:54Discover the USE_M_TIME #ifdef in init.c and check out the Makefile of other demos that call handle_m_time_interrupt() to find that they contain the flag -DUSE_M_TIME

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38:54Discover the USE_M_TIME #ifdef in init.c and check out the Makefile of other demos that call handle_m_time_interrupt() to find that they contain the flag -DUSE_M_TIME

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38:54Discover the USE_M_TIME #ifdef in init.c and check out the Makefile of other demos that call handle_m_time_interrupt() to find that they contain the flag -DUSE_M_TIME

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40:35Add -DUSE_PLIC and -DUSE_M_TIME to the pwm_speed_test Makefile

42:00Run the program to find that it now works beautifully

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42:00Run the program to find that it now works beautifully

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42:00Run the program to find that it now works beautifully

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42:20Delete all the timer interrupt code, in favour of the PLIC code

46:59Run the program to see "Hello, World" but no interrupt or trap

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46:59Run the program to see "Hello, World" but no interrupt or trap

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46:59Run the program to see "Hello, World" but no interrupt or trap

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48:47Compare our PLIC code with that in global_interrupts.c, try to change PWM0_REG(PWM_CMP0) to PWM0_REG(PWM_COUNT), and instead uncomment the PLIC_set_priority() call in main()

53:15Run the program and hit our PWM interrupt!

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53:15Run the program and hit our PWM interrupt!

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53:15Run the program and hit our PWM interrupt!

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53:44Determine to go back to timing

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53:44Determine to go back to timing

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53:44Determine to go back to timing

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55:40Read Chapter 15 - E300 Pulse-Width Modulation (PWM) Peripheral⁴

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55:40Read Chapter 15 - E300 Pulse-Width Modulation (PWM) Peripheral⁴

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55:40Read Chapter 15 - E300 Pulse-Width Modulation (PWM) Peripheral⁴

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56:42Try setting PWM0_REG(PWM_CMP0) = 0xFFFF

57:30Run the program to see that our interrupts fire pretty fast

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57:30Run the program to see that our interrupts fire pretty fast

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57:30Run the program to see that our interrupts fire pretty fast

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57:51Try to add 0x1 to the timer rearming call

58:11Run the program to see that our interrupts still fire pretty fast

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58:11Run the program to see that our interrupts still fire pretty fast

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58:11Run the program to see that our interrupts still fire pretty fast

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58:26Bump straight up to 0x7 in the timer rearming call

58:44Run the program to see that our interrupts still fire pretty fast

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58:44Run the program to see that our interrupts still fire pretty fast

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58:44Run the program to see that our interrupts still fire pretty fast

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1:00:42Note that we wanted to be in one-shot mode, and try making pwm_0_handler() clear the PWM_CFG register

1:02:05Run the program to see that we are correctly in one-shot mode

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1:02:05Run the program to see that we are correctly in one-shot mode

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1:02:05Run the program to see that we are correctly in one-shot mode

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1:02:44Rearm the timer in pwm_0_handler()

1:03:53Run the program to see that the timer gets rearmed each time, and note that it still runs pretty fast

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1:03:53Run the program to see that the timer gets rearmed each time, and note that it still runs pretty fast

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1:03:53Run the program to see that the timer gets rearmed each time, and note that it still runs pretty fast

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1:05:02Consider the main use-case of PWM interrupts being for debouncing, and plug the Guide to Debouncing⁵

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1:05:02Consider the main use-case of PWM interrupts being for debouncing, and plug the Guide to Debouncing⁵

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1:05:02Consider the main use-case of PWM interrupts being for debouncing, and plug the Guide to Debouncing⁵

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1:11:04Consider alternate ways to handle debouncing, and uses for PWM interrupts

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1:11:04Consider alternate ways to handle debouncing, and uses for PWM interrupts

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1:11:04Consider alternate ways to handle debouncing, and uses for PWM interrupts

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1:14:24Determine that we have a good understanding of global_interrupts, and to start fully learning timing in the next episode

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1:14:24Determine that we have a good understanding of global_interrupts, and to start fully learning timing in the next episode

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1:14:24Determine that we have a good understanding of global_interrupts, and to start fully learning timing in the next episode

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1:15:44Plug the new Gumroad-powered subscription solution⁶, along with a note that the Transparency Reports alone remain solely available publicly on Patreon⁷

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1:15:44Plug the new Gumroad-powered subscription solution⁶, along with a note that the Transparency Reports alone remain solely available publicly on Patreon⁷

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1:15:44Plug the new Gumroad-powered subscription solution⁶, along with a note that the Transparency Reports alone remain solely available publicly on Patreon⁷

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