AM3352: Sequence to disable a interface clock

Hi,

Are you developing on Processor SDK TI-RTOS? If yes, please read this: e2e.ti.com/.../notice-regarding-processor-sdk-ti-rtos-for-am335x-am437x-omap-l13x-c674x-k2g-amic110-amic120-devices

Regards,

Vaibhav

Hi Vaibhav,

I want to manually disable one UART module clock to verify another issue. RTOS based code would be more readable, but I won't ask for that as it will be rejected and closed. 

So I only need the operation steps description to do that, I can implement it by myself.

Actually I checked AM335x Starterware and RTOS SDK, did not find such feature implementation to disable a module/interface clock.

Try the following Disable Sequence

1. Ensure UART1 is idle before disabling:
   - TX FIFO and shift registers must be empty
   - RX FIFO must be empty
   - RX line must be idle [3]
2. Changing control registers while the module is busy communicating will cause errors [4].
3. Configure UART idle mode:
   1. Check `UART1.UART_SYSC[4:3]` IDLEMODE bits to ensure the module can acknowledge idle requests [3].
4. Write MODULEMODE=0x0:
   1. CM_PER_UART1_CLKCTRL = 0x0;
5. Poll IDLEST until it reaches 0x3
   1. while ((CM_PER_UART1_CLKCTRL & 0x30000) != 0x30000) {
      // Wait for transition to complete
      }

I think I followed up steps, except don't know how to check if RX line idle status, still keep in transition status. 

Actually I just enabled UART1, did not connect it to external component, there is no data on data line.

root@am335x-evm:~# dmesg |grep ttyS*
[    0.000000] Kernel command line: root=PARTUUID=84550dbc-02 rootwait rw earlycon console=ttyO0,115200n8,115200
[    0.034459] WARNING: Your 'console=ttyO0' has been replaced by 'ttyS0'
[    1.619071] 48022000.serial: ttyS1 at MMIO 0x48022000 (irq = 18, base_baud = 3000000) is a 8250
[    2.240622] 44e09000.serial: ttyS0 at MMIO 0x44e09000 (irq = 37, base_baud = 3000000) is a 8250
[    2.258610] printk: console [ttyS0] enabled
[    4.980157] systemd[1]: Created slice Slice /system/getty.
[    5.064310] systemd[1]: Created slice Slice /system/serial-getty.
root@am335x-evm:~# devmem2 0x48022054
/dev/mem opened.
Memory mapped at address 0xb6f36000.
Read at address  0x48022054 (0xb6f36054): 0x00000009
root@am335x-evm:~# devmem2 0x48022014
/dev/mem opened.
Memory mapped at address 0xb6ff7000.
Read at address  0x48022014 (0xb6ff7014): 0x00000060
root@am335x-evm:~# devmem2 0x44e0006c
/dev/mem opened.
Memory mapped at address 0xb6fd0000.
Read at address  0x44E0006C (0xb6fd006c): 0x00000002
root@am335x-evm:~# devmem2 0x44e0006c w 0
/dev/mem opened.
Memory mapped at address 0xb6f5e000.
Read at address  0x44E0006C (0xb6f5e06c): 0x00000002
Write at address 0x44E0006C (0xb6f5e06c): 0x00000000, readback 0x00000000
root@am335x-evm:~# devmem2 0x44e0006c
/dev/mem opened.
Memory mapped at address 0xb6f04000.
Read at address  0x44E0006C (0xb6f0406c): 0x00010000
root@am335x-evm:~# 
root@am335x-evm:~# devmem2 0x48022014
/dev/mem opened.[ 1033.353309] 8<--- cut here ---
[ 1033.357534] Unhandled fault: external abort on non-linefetch (0x1018) at 0xb6f78014
[ 1033.365236] [b6f78014] *pgd=b133a831

Memory mapped at address 0xb6f78000.
Bus error (core dumped)
root@am335x-evm:~# devmem2 0x48022054
/dev/mem opened.[ 1058.553668] 8<--- cut here ---
[ 1058.557871] Unhandled fault: external abort on non-linefetch (0x1018) at 0xb6f18054
[ 1058.565578] [b6f18054] *pgd=bb811831

Memory mapped at address 0xb6f18000.
Bus error (core dumped)
root@am335x-evm:~# 
CTRL-A Z for help | 1

Hi Tony,

Looking into this and will get back to you in sometime.

Regards,

Vaibhav

Hello,

The subject matter expert is out of office until April 29th. Please expect a delayed response. Thank you.

Hi Tony,

Tony Tang said:

I want to manually disable one UART module clock to verify another issue.

The clock management for AM335x is done by the clk drivers. I never looked into it to understand the clk enable/disable sequences, but if you just want to disable the clock for a UART, you can do so by unbinding the UART driver from the UART device in Linux sysfs.