2015-02-13 11:00 GMT+01:00 Uwe Kleine-König [off-list ref]:

On Fri, Feb 13, 2015 at 09:42:46AM +0100, Maxime Coquelin wrote:

quoted

Hi Geert,

2015-02-12 21:34 GMT+01:00 Geert Uytterhoeven [off-list ref]:

quoted

On Thu, Feb 12, 2015 at 6:45 PM, Maxime Coquelin
[off-list ref] wrote:

quoted

From Cortex-M4 and M7 reference manuals, the nvic supports up to 240
interrupts. So the number of entries in vectors table is 256.

This patch adds the missing entries, and change the alignement, so that
vector_table remains naturally aligned.

Shouldn't this depend on ARCH_STM32, or some other M4 or M7 specific
Kconfig option, to avoid wasting the space on other CPUs?

Actually, the STM32F429 has 90 interrupts, so it would need 106
entries in the vector table.
The maximum of supported interrupts is not only for Cortex-M4 and M7,
this is also true for Cortex-M3.

I see two possibilities:
 1 - We declare the vector table for the maximum supported number of
IRQs, as this patch does.
        - Pro: it will be functionnal with all Cortex-M MCUs
        - Con: Waste of less than 1KB for memory
 2 - We introduce a config flag that provides the number of interrupts
        - Pro: No more memory waste
        - Con: Need to declare a per MCU model config flag.

I'd vote for 2, something like:

        config CPUV7M_NUM_IRQ
                int
                default 90 if STM32F429
                default 38 if EFM32GG
                default 240

then there is a working default and platforms being short on memory can
configure as appropriate. (The only down side is that if we create
multi-platfrom images at some time in the future either all or none of
the supported platforms must provide a value here.)

Ok, I'm fine doing this way.
I will implement this in the v2 if Russel is fine with the proposal too.

quoted

Then, regarding the natural alignment, is there a way to ensure it
depending on the value of a config flag?

The exact wording in ARMARMv7-M is:

        The Vector table must be naturally aligned to a power of two
        whose alignment value is greater than or equal
        to (Number of Exceptions supported x 4), with a minimum
        alignment of 128 bytes.

quoted

Or we should keep it at the maximum value possible?

So we need:

        .align x

with x being max(7, ceil(log((CPUV7M_NUM_IRQ + 16) * 4, 2))). So the
alignment needed is between 7 and 10.

If the assembler supports an expression here I'd use that. But before
adding strange hacks to generate the right value there better go for a
static value like:

        /* The vector table must be naturally aligned */
        #if CONFIG_CPUV7M_NUM_IRQ <= 112
        .align 9 /* log2((112 + 16) * 4) */
        #else
        .align 10
        #endif

Further steps would be:

        CONFIG_CPUV7M_NUM_IRQ <= 48 -> .align 8
        CONFIG_CPUV7M_NUM_IRQ <= 16 -> .align 7

Probably it's not worth to add the respective #ifdefs here.

I will go for the  #ifdefs.

Thanks,
Maxime

Best regards
Uwe

--
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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