cpu/sam0_common: Implement time-sharing of SERCOMs #21029
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| @@ -281,55 +248,47 @@ static void _spi_acquire(spi_t bus, spi_mode_t mode, spi_clk_t clk) | |||
| * to mitigate the rounding error due to integer arithmetic, the | |||
| * equation is modified to | |||
| * BAUD.reg = ((f_ref + f_bus) / (2 * f_bus) - 1) */ | |||
| const uint8_t baud = (gclk_src + clk) / (2 * clk) - 1; | |||
| uint8_t baud = (gclk_src + clk) / (2 * clk) - 1; | |||
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why do you unconst this (line seems uncanged otherwise)
same for ctrla
liter (const correctness) might not like that change
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For consistency with the other variables holding the values to store into the registers.
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This adds a `periph_sercom` feature and implementation which
`periph_i2c`, `periph_uart`, and `periph_spi` are implemented on top.
This allows for sharing a single SERCOM instance to provide multiple
serial interfaces (in round-robin time-sharing fashion).
Note: In practice, a SERCOM can often not be shared if it needs to
provide an UART.
Background:
While code using the I2C/SPI APIs is already optimized to share the
peripheral with `i2c_acquire()`/`spi_acquire()` and
`i2c_release()`/`spi_release()`, UARTs are typically not shared and most
users will not call `uart_poweron()` and `uart_poweroff()` to only have
the SERCOM in UART mode when actually needed. Worse: For many use cases
(such as stdin), the UART will need to be constantly running, as
receiving data happens asynchronously at unpredictable points in time.
For `gpio_ll_print_conf()` we need to include `<stdio.h>`, when not using `fmt.h`.
Now that time-sharing SERCOMs is possible, we can provide the SPI on D11/D12/D13 (backed by SERCOM3) also when the UART on D0/D1 (also backed by SERCOM3) is used.
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| #if defined(CPU_COMMON_SAMD21) | ||
| PM->APBCMASK.reg |= (PM_APBCMASK_SERCOM0 << sercom); | ||
| #elif defined (CPU_COMMON_SAMD5X) | ||
| if (sercom < 2) { | ||
| MCLK->APBAMASK.reg |= (1 << (sercom + 12)); | ||
| } else if (sercom < 4) { | ||
| MCLK->APBBMASK.reg |= (1 << (sercom + 7)); | ||
| } else { | ||
| MCLK->APBDMASK.reg |= (1 << (sercom - 4)); | ||
| } | ||
| #else | ||
| if (sercom < 5) { | ||
| MCLK->APBCMASK.reg |= (MCLK_APBCMASK_SERCOM0 << sercom); | ||
| } | ||
| #if defined(CPU_COMMON_SAML21) | ||
| else { | ||
| MCLK->APBDMASK.reg |= (MCLK_APBDMASK_SERCOM5); | ||
| } | ||
| #endif /* CPU_COMMON_SAML21 */ |
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Since you basically have an #ifdef case for each CPU family, I think it would be more readable to move _sercom_apb_enable() to periph_cpu.h of the respective CPU family memember.
So you'd only be left with
static inline void _sercom_apb_enable(sercom_t sercom)
{
PM->APBCMASK.reg |= PM_APBCMASK_SERCOM0 << sercom;
}on samd21 and
static inline void _sercom_apb_enable(sercom_t sercom)
{
MCLK->APBCMASK.reg |= MCLK_APBCMASK_SERCOM0 << sercom;
}on saml1x, etc
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Contribution description
This adds a
periph_sercomfeature and implementation whichperiph_i2c,periph_uart, andperiph_spiare implemented on top. This allows for sharing a single SERCOM instance to provide multiple serial interfaces (in round-robin time-sharing fashion).Note
In practice, a SERCOM can often not be shared if it needs to provide an UART.
Background:
While code using the I2C/SPI APIs is already optimized to share the peripheral with
i2c_acquire()/spi_acquire()andi2c_release()/spi_release(), UARTs are typically not shared and most users will not calluart_poweron()anduart_poweroff()to only have the SERCOM in UART mode when actually needed. Worse: For many use cases (such as stdin), the UART will need to be constantly running, as receiving data happens asynchronously at unpredictable points in time.Testing procedure
make BOARD=adafruit-metro-m4-express flash term -C tests/periph/selftest_shield2024-11-21 20:29:42,410 # ALL TESTS SUCCEEDEDIssues/PRs references
None