We're porting Apache #NuttX RTOS to @PINE64 Star64 #JH7110 SBC ... Let's talk about the #RISCV Privilege Levels and UART Registers

Article: https://lupyuen.codeberg.page/articles/privilege

Guess why this UART code loops forever on Star64 #JH7110 #RISCV SBC

Article: https://lupyuen.codeberg.page/articles/privilege.html#wait-forever-in-uart-transmit

Here's the answer: UART Registers on Star64 #JH7110 are spaced differently from QEMU!

Article: https://lupyuen.codeberg.page/articles/privilege.html#uart-registers-are-spaced-differently

Let's find out why #NuttX on Star64 #JH7110 gets stuck ... When we enter a Critical Section

Article: https://lupyuen.codeberg.page/articles/privilege.html#critical-section-doesnt-return

#RISCV "mstatus" Register won't work in #NuttX RTOS because we're running in Supervisor Mode ... Let's fix it for #JH7110

Article: https://lupyuen.codeberg.page/articles/privilege.html#critical-section-doesnt-return

We change #RISCV "mstatus" to "sstatus" in Apache #NuttX RTOS ... Because it runs in Supervisor Mode on Star64 #JH7110

Article: https://lupyuen.codeberg.page/articles/privilege.html#risc-v-privilege-levels

Switching #NuttX from #RISCV Machine Mode to Supervisor Mode

Article: https://lupyuen.codeberg.page/articles/privilege.html#risc-v-machine-mode-becomes-supervisor-mode

#NuttX Kernel Mode executes NuttX Apps in unprivileged User Mode

Article: https://lupyuen.codeberg.page/articles/privilege.html#nuttx-flat-mode-becomes-kernel-mode

Fixing the #RISCV Machine Mode registers for Star64 #JH7110 SBC

Article: https://lupyuen.codeberg.page/articles/privilege.html#initialise-risc-v-supervisor-mode