Access to RTC from Cortex-M4 on i.MX8M Mini

Patryk — Tue, 05 Apr 2022 08:41:15 GMT

Hi,
I am using Cortex-M4 with FreeRTOS to communicate with an external sensor. The data is received by the M4 and available to the A53 via RPMsg. It works fine. Additionally, I would like to be able to configure the internal RTC using A53 and read the time from the RTC using M4. It is possible? Currently with Linux running on A53 I can set and get the time from RTC (SNVS_LP). I tried to read value from RTC with M4 directly from registers but unfortunately can't do that.

Function for read time in Cortex-M4:

static uint32_t SNVS_LP_RTC_GetSeconds(SNVS_Type *base) { uint32_t seconds = 0; uint32_t tmp = 0; /* Do consecutive reads until value is correct */ do { seconds = tmp; tmp = (base->LPSMCMR << 17U); tmp |= (base->LPSMCLR >> 15U); } while (tmp != seconds); return seconds; }

Device tree configuration:

snvs: snvs@30370000 { compatible = "fsl,sec-v4.0-mon","syscon", "simple-mfd"; reg = <0x30370000 0x10000>; snvs_rtc: snvs-rtc-lp { compatible = "fsl,sec-v4.0-mon-rtc-lp"; regmap = <&snvs>; offset = <0x34>; interrupts = <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 20 IRQ_TYPE_LEVEL_HIGH>; clocks = <&clk IMX8MM_CLK_SNVS_ROOT>; clock-names = "snvs-rtc"; }; snvs_pwrkey: snvs-powerkey { compatible = "fsl,sec-v4.0-pwrkey"; regmap = <&snvs>; interrupts = <GIC_SPI 4 IRQ_TYPE_LEVEL_HIGH>; clocks = <&clk IMX8MM_CLK_SNVS_ROOT>; clock-names = "snvs"; linux,keycode = <KEY_POWER>; wakeup-source; status = "disabled"; }; };

In the documentation I found information that: "The SNVS_HP provides an interface between SNVS_LP and the rest of the system", so I modified ATF in the following way:

--- a/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c 2022-01-25 15:28:29.000000000 +0100 +++ b/plat/imx/imx8m/imx8mm/imx8mm_bl31_setup.c 2022-01-25 15:42:05.000000000 +0100 @@ -58,8 +58,7 @@ RDC_MDAn(RDC_MDA_M4, DID1), /* peripherals domain permission */ - RDC_PDAPn(RDC_PDAP_UART4, D0R | D0W), - RDC_PDAPn(RDC_PDAP_UART2, D0R | D0W), + RDC_PDAPn(RDC_PDAP_eCSPI2, D1R | D1W), + RDC_PDAPn(RDC_PDAP_SNVS_HP, D1R | D0R | D0W), /* memory region */

I am confused on how to access the RTC with Cortex-M4 and kindly ask for help.

Thank you in advance for your help

Best Regards,

Patryk

Re: Access to RTC from Cortex-M4 on i.MX8M Mini

RoccoBr — Thu, 21 Apr 2022 08:46:41 GMT

Hello,

I'm trying to achieve the same.

this is the dump of the registers

SNVS_HP Command Register: 80002100
SNVS_HP Control Register: 0
SNVS_HP Status Register: 80009b00
SNVS_HP Real Time Counter MSB Register: 0
SNVS_HP Real Time Counter LSB Register: 0

SNVS_LP Control Register: 21
SNVS_LP Status Register: 40000000
SNVS_LP Lock Register: 0
SNVS_LP Real Time Counter MSB Register: 0
SNVS_LP Real Time Counter LSB Register: 0

Writing 1 to SNVS_HP Control Register will enable the HP real time counter, but then it will become just another independent real time counter at 32KHz, that's not want we want.

SNVS_LP Real Time Counter is always returning 0 , that is strange as bit 31 in SNVS_HP Command Register should guarantee access to privileged registers.

i.MX ProcessorsのトピックRe: Access to RTC from Cortex-M4 on i.MX8M Mini

Access to RTC from Cortex-M4 on i.MX8M Mini

Re: Access to RTC from Cortex-M4 on i.MX8M Mini