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wrpll: clarify comment

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This commit is contained in:
Sebastien Bourdeauducq 2019-12-31 11:36:26 +08:00
parent 1e864b7e2d
commit bb04b082a7
1 changed files with 2 additions and 1 deletions
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artiq/firmware/libboard_artiq/wrpll.rs
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@ -267,7 +267,8 @@ mod si549 {
fn get_frequencies() -> (u32, u32, u32) { fn get_frequencies() -> (u32, u32, u32) {
unsafe { unsafe {
csr::wrpll::frequency_counter_update_en_write(1); csr::wrpll::frequency_counter_update_en_write(1);
clock::spin_us(200_000); // wait for at least one update // wait for at least one full update cycle (> 2 timer periods)
clock::spin_us(200_000);
csr::wrpll::frequency_counter_update_en_write(0); csr::wrpll::frequency_counter_update_en_write(0);
let helper = csr::wrpll::frequency_counter_counter_helper_read(); let helper = csr::wrpll::frequency_counter_counter_helper_read();
let main = csr::wrpll::frequency_counter_counter_rtio_read(); let main = csr::wrpll::frequency_counter_counter_rtio_read();